CHAPTER 4 NATURAL HAZARDS RISK ASSESSMENT

Transcription

1 CHAPTER 4 NATURAL HAZARDS RISK ASSESSMENT Requirement 201.6(c)(2): [The plan shall include] A risk assessment that provides the factual basis for activities proposed in the strategy to reduce losses from identified hazards. Local risk assessments must provide sufficient information to enable the jurisdiction to identify and prioritize appropriate mitigation actions to reduce losses from identified hazards. As defined by the Federal Emergency Management Agency (FEMA), risk is a combination of hazard, vulnerability, and exposure. It is the impact that a hazard would have on people, services, facilities, and structures in a community and refers to the likelihood of a hazard event resulting in an adverse condition that causes injury or damage. The risk assessment process identifies and profiles relevant hazards and assesses the exposure of lives, property, and infrastructure to these hazards. The process allows for a better understanding of a jurisdiction s potential risk to natural hazards and provides a framework for developing and prioritizing mitigation actions to reduce risk from future hazard events. This risk assessment followed the methodology described in the FEMA publication Understanding Your Risks Identifying Hazards and Estimating Losses (FEMA 386-2, 2002), which breaks the assessment down to a four-step process: 1) Identify Hazards 2) Profile Hazard Events 3) Inventory Assets 4) Estimate Losses Data collected through this process has been incorporated into the following sections of this chapter: Section 4.1: Hazard Identification. Identifies the hazards which threaten the planning area and describe why some hazards have been omitted from further consideration. Discusses the research methodology utilized to gather the data in this plan. Section 4.2: Hazard Profiles. Discusses each of the included hazards which threaten the planning area. Provides a brief definition and overview of the hazard and reviews significant previous occurrences of the hazard. Includes the following sub-sections for each hazard: description, geographic extent, previous occurrences, probability of future occurrences, exposure assessment, impact assessment, estimating potential losses and development trends assessment, and overall vulnerability summary. Section 4.3: Vulnerability Summary. Provides a county-wide analysis of exposure to hazards. This is a general picture that assesses common exposures for all hazards and includes specific data such as demographics, property values, and critical facilities. Combines the estimation of a hazard s occurrence probability with the associated Dane County 4.1

2 vulnerabilities of critical infrastructure and populations. Includes a summary of the hazard risk ratings and prioritizes hazards for mitigation implementation purposes. Section 4.4: Mitigation Capabilities Assessment. An inventory of existing mitigation activities and existing policies, regulations, and plans that pertain to mitigation and affect the County s net vulnerability. 4.1 Hazard Identification Requirement 201.6(c)(2)(i): [The risk assessment shall include a] description of the type of all natural hazards that can affect the jurisdiction Methodology The risk assessment is the basis of the County s hazard mitigation strategy. As used here, risk assessment means the evaluation of the impact of natural hazards on the human-built environment, businesses, social structure and services, and the natural environment. The risk assessment is essential. It allows the multi-jurisdictional participants to develop targeted mitigation strategies to reduce exposure and potential for loss, which is addressed in the next chapter. There are various risk assessment methodologies, which differ by focus and scale. FEMA recommends an analysis focused on critical facilities and the potential for future economic losses. Other methods focus on social characteristics and the ability of society to adapt to the hazard. Scale varies from analyzing the direct impact of a single event to examining the complex interplay of events and hazards and the potential ripple effects of hazards. Spatial scales range from the analysis of a hazard s impact on a single, local government through analyzing county, state, or even federal-wide impacts. The chapter identifies the hazards first. Then, the hazard profiles and vulnerability assessments are combined, and each hazard is discussed separately. A generalized risk analysis follows which interprets the general findings and includes a graphic representation. Finally, a capabilities assessment discusses the county-wide mitigation procedures and tools already in place, utilizing a multi-hazard approach. Specific jurisdictional considerations are included in the relevant jurisdictional attachments. The specific method for profiling and assessing vulnerability varies between hazards and is described in detail in each section but they all follow the same general format Potential Hazards List The Dane County Hazard and Risk Analysis, an Appendix to the County s Emergency Operations Plan (EOP), served as the starting point for the initial risk assessment. Based on the Hazard Analysis and input from the Citizens Advisory Committee, the planning committee considered 11 hazards for the original plan developed in The review conducted in re-examined these hazards, as well as conducted additional research to identify other hazards which should be included in this document. County-wide participation from villages, towns and the City of Madison provided localized knowledge and information to update the plan. Only natural hazards are considered in this document. Dane County 4.2

3 Based on the recommendations by FEMA, the HMPC, and historical records for Dane county, the following hazards (listed alphabetically), were considered during the plan update: Dam Failure Drought Earthquake Erosion Expansive Soils Flood Fog Hailstorm Landslides Levee Failure Lightning Severe Cold Excessive heat Severe Thunderstorm Severe Winter Storm Subsidence Tornado Wildfire Windstorm Dane County 4.3

4 Table 4.1 Preliminary Hazard Ranking by the 2009 Hazard Mitigation Planning Committee Hazard Area of impact Hazard Attributes Rating: (1-2-3) Past history, probability of future occurrence Short term time factors Primary Impact (Short Term Life and Property) Impact on General Structures Impact on Critical Facilities Impact Attributes Rating: ( ) Impact on At-Risk Populations Secondary Impact (Long Term Community Impacts) Social Impact Economic Impact Severity of other associated secondary hazards Total Dam/Levee Failure Extreme Cold Extreme Heat Drought Erosion Flood Fog Hail Storm Landslide Lightning Tornado Wildfire Windstorm Winter Storm Land Subsidence Elevated groundwater Source: Data Collection Guides Dane County 4.4

5 This table was distributed to the members of the initial planning committee when the Hazard Mitigation was first drafted in The committee members each completed the table using their own experiences and judgment to assign the numeric values. As part of the update process, all participating members of the HMPC were distributed blank versions of this table again. The input from Dane County government is represented above. This served as the preliminary hazard ranking process for the 2009 Update, which provided focus and scope for the hazard mitigation planning committee and the update team. According to this table, the HMPC ranked Tornado as the most dangerous and costly hazard, with Winter Storms, Floods, Elevated Groundwater Tables, Windstorms, Extreme Heat and Extreme Cold, Hail Storms, Dam Failures, Lightning, Erosion, Subsidence, Fog and Landslides following. Some hazards listed in this table were later combined/consolidated as described in the next section. Hazard ranking worksheets for individual jurisdictions are presented in their respective annex. This table and additional hazard vulnerability tables in each annex serve the purpose of differentiating the jurisdiction s risk from each hazard, as they vary from that of the planning area as a whole. Unique or varied risks are discussed in the annex, where applicable Hazards Not Included, Added, Modified or Combined After conducting a cursory review of Dane County s geographic location and climate, several of the natural hazards included in the initial composite list were discarded because they are not relevant to Dane County. These include: Avalanche, Costal Erosion, Costal Storm, Earthquake, Expansive Soils, Hurricane, Tsunami, and Volcano. Earthquake was considered during the 2009 update, but did not warrant a full hazard profile, as the probability of a damaging event is extremely low based on an analysis associated with the Wisconsin State Hazard Mitigation Plan. Severe Thunderstorm is not included because the damaging effects of such storms (hail, lightning, and high wind) are profiled as individual hazards as this better reflects the individual hazard risks and occurrences for Dane County. Levee failures were researched but there are no documented levees in Dane County, so the hazard was removed from the list. Severe Cold was expanded to include Wind-chill factors. Several new hazards were profiled for the 2009 update, including Dam Failures, Erosion, Landslides and Sinkholes, and Elevated Groundwater Tables. Elevated Groundwater Tables is profiled as part of the Flood hazard, and Landslides and Sinkholes and Erosion are addressed in a single chapter, due to their similar geologic characteristics Final Hazards List (updated ) As updated during the plan review conducted in , the final hazards which are extensively profiled, including significant vulnerability assessment, risk analysis, and impact assessments, are listed in alphabetical order: Dam Failure Drought Flood Fog Hailstorm Landslide, Sinkholes and Erosion Lightning Severe Cold & Wind-chill Excessive heat Dane County 4.5

6 Severe Winter Storm Tornado Wildfire Windstorms Disaster Declaration History As part of the hazard identification process, the HMPC researched past events which triggered federal and/or state emergency or disaster declarations in the planning area. Federal and/or state disaster declarations may be granted when the severity and magnitude of an event surpasses the ability of the local government to respond and recover. Disaster assistance is supplemental and sequential. When the local government s capacity has been surpassed, a state disaster declaration may be issued, allowing for the provision of state assistance. Should the disaster be so severe that both the local and state governments capacities are exceeded, a federal emergency or disaster declaration may be issued allowing for the provision of federal assistance. There have been 16 disaster or emergency declarations in Dane County since Table 4.2 details these disasters. Table 4.2 Disaster Declarations for Dane County Year Disaster Type Declaration Type Damage Assessment 1976 Ice Storm Presidential Disaster $1.22 Million (Public Assistance) 1976 Drought Presidential Emergency $625 Million (statewide) 1978 Flooding and Tornados Presidential Disaster $180,000 (Public Assistance) 1984 Tornados Presidential Disaster $775,394 (Public Assistance) $11,168,220 (Individual Assistance) Dane and Iowa Counties combined 1990 Flooding and Tornados Presidential Disaster $37,000 (Public Assistance) $30,343 (Individual Assistance) 1991 Severe Storms (Windstorm) Presidential Disaster $1.33 Million (Public Assistance) 1992 Tornados Presidential Disaster $163,000 (Public Assistance) 1993 Flooding Presidential Disaster 1996 Flooding and Severe Storms Local Sources High Winds and Severe Storms Severe Storms (Windstorm) and Flooding Local Sources Presidential Disaster $888,000 (Public Assistance) $1,439,332 (Individual Assistance) $22.6 Million (Total Damages) $940,000 (Public Assistance) $1,2248,684 (Individual Assistance) $3.3 Million (Total Damages) $586,000 (Public Assistance) $940,000 (Public Assistance) $1,248,684 (Individual Assistance) $9.3 Million (Total Damages) 2000 Snow Emergency Presidential Emergency $586,000 (Public Assistance) 2004 Severe Storms and Tornados Presidential Disaster $1.5 Million (Public Assistance) 2005 Stoughton Tornado State Disaster Fund $35 Million (Public Assistance) 2007 Flooding Presidential Disaster FEMA PDA- $3,294,210 Private $1,643,101 Public 758 homes impacted 1 Wisconsin Emergency Management County Disasters since Available online at last accessed February 11, Dane County 4.6

7 Year Disaster Type Declaration Type Damage Assessment 2008 Snow Emergency Presidential Emergency $1,439,206 (Public Assistance) 2008 Severe Storms, Tornados and Flooding Presidential Disaster Source: Wisconsin Emergency Management and FEMA Major Disaster Declarations Website $1,533,659 (Public Assistance) $1.76 Million (Individual Assistance) $1.64 Million (Housing Assistance) $120k other needs, 1,635 households requested aid Total damages $35,789,723 In addition to property losses, there is potential for death or injury from many of the natural hazards that threaten the County. Figure 4.1 depicts the total number of tornados, floods, hail, lightning events and thunderstorm-force winds in Wisconsin from 1982 to The map shows the events by county and also denotes the number of directly related deaths and injuries to these severe weather events. Dane County has more documented severe weather events than any other county in Wisconsin, with nearly 200 more events than the next closest county. Though Dane County has not experienced as many fatalities directly related to these severe hazards, the numbers indicate that the potential for greater loss of life exists. Dane County does have one of the highest injury rates, which is a likely corollary to a high event occurrence and a high population count. Table 4.3 and Table 4.4 also depict weather-related deaths and injuries, but include additional information regarding heat wave, winter storm, and cold wave-related death and injury. Clearly, natural hazards present a significant threat to the population of Dane County. The past and potential impacts for each of the identified hazards are described in greater detail in each specific hazard profile. Dane County 4.7

8 Figure 4.1 Total Severe Weather Events in Wisconsin ( ) Source: National Weather Service Dane County 4.8

9 Table 4.3 Wisconsin Weather Related Fatalities ( ) YEAR Tornado Wind Hail Flooding Lightning Heat Waves Winter Storms Cold Wave / / / / / / / / / / / /0 0 4 Total / Note: Deaths listed above are direct deaths, in which the weather hazard is the major cause of death. However, for heat waves, the heat and humidity are sometimes labeled as secondary or contributing causes of death. These are indirect deaths, which if shown, is the second number in the heat wave column. Likewise, nearly all deaths attributed to vehicle deaths on highways in Winter Storms are indirect deaths, since the driver was driving too fast for the conditions, etc. In other words, the snow or ice did not kill the individual; the death was the result of a vehicle accident. Source: National Weather Service Dane County 4.9

10 Table 4.4 Wisconsin Weather-Related Injuries ( ) Year Tornado Wind Hail Flooding Lightning Heat Waves Winter Storms Cold Waves Total Note: All the injuries listed above are direct injuries, in which the weather hazard is the major cause of injury. Heat Wave injuries are considered illnesses. And are not are not tabulated above. Likewise, nearly all injuries attributed to vehicle injuries on highways in Winter Storms are indirect injuries, since the driver was driving too fast for the conditions, etc. In other words, the snow or ice did not injure the individual; the injury was the result of a vehicle accident. Source: National Weather Service Dane County 4.10

11 4.2 Hazard Profiles Requirement 201.6(c)(2)(i): [The risk assessment shall include a] A description of the type, location, and extent of all natural hazards that can affect the jurisdiction. The plan shall include information on previous occurrences of hazard events[.] Requirement 201.6(c)(2)(ii): [The plan shall also include] A description of the jurisdiction's vulnerability to the hazards described in paragraph (c)(2)(i) of this section. This description shall include an overall summary of each hazard and its impact on the community. All plans approved after October 1, 2008 must also address NFIP insured structures that have been repetitively damaged by floods. (A) The types and numbers of existing and future buildings, infrastructure, and critical facilities located in the identified hazard areas; (B) An estimate of the potential dollar losses to vulnerable structures identified in paragraph (c)(2)(i)(a) of this section and a description of the methodology used to prepare the estimate; (C) Providing a general description of land uses and development trends within the community so that mitigation options can be considered in future land use decisions. The hazards identified in Section Final Hazards List (updated ) are profiled individually in this section. Much of the profile information came from the same sources used to identify the hazards during the initial planning effort in The information was reviewed for accuracy and applicability and updated where required. Significant occurrences of hazards that have occurred since the original plan s adoption in 2004 are also included in the updated hazard profiles Profile Methodology Each hazard is profiled in a similar format that is described below. This approach helps create a uniform planning basis and enables comparisons between the hazards. The basic outline is: Hazard Profile This provides the basic information for the hazard. For organizational purposes, this information is divided into the following subsections. This section fulfills Sections 5 and 6 of the FEMA Local Mitigation Plan Review Crosswalk. Description: This subsection gives a generic description of the hazard and associated problems, followed by details on the hazard specific to Dane County. Geographic Extent: This subsection discusses which areas of the County are most likely to be affected by a hazard event at any given time: Isolated: Single site occurrences for each incident Limited: Less than 10 percent of the planning area Significant: 10 to 50 percent of the planning area Extensive: 50 to 100 percent of the planning area Dane County 4.11

12 Previous Occurrences: This subsection contains information on historic incidents, including impacts where known. The extent or location of the hazard within or near the Dane County planning area is also included here. Information provided by the HMPC is included here along with information from other data sources. Citations are provided as footnotes. Probability of Future Occurrences: The frequency of past events is used here to gauge the likelihood of future occurrences. Based on historical data, the likelihood of future occurrences is categorized into one of the following classifications: Unlikely: Between.1 and 1 percent chance of occurrence in the next 100 years, or has a recurrence interval of greater than every 100 years. Occasional: Between 1 and 10 percent chance of occurrence in the next year, or has a recurrence interval of 11 to 100 years Likely: Between 10 and 100 percent chance of occurrence in the next year, or has a recurrence interval of 10 years or less Highly Likely: Near 100 percent chance of occurrence in the next year, or happens yearly. The frequency, or chance of occurrence, was calculated where possible based on existing data. Frequency was determined by dividing the number of events observed by the number of years and multiplying by 100. This gives the percent chance of event happening in any given year. Where this data results in a percent above 100 percent, the hazard is assumed to have a yearly frequency rating. Example: Three droughts over a 30-year period equates to 10 percent chance that the hazard will occur in a given year, and is then rated as likely. Impact Assessment This examines the potential impacts of the hazard on Dane County using qualitative assessment methods. Based on past experiences in Dane County, in the State of Wisconsin, and nationwide, this is a qualitative discussion of the consequences that could be expected in the aftermath of each of the hazard events. The section fulfills Sections 7, 8, and 9 Element A of the FEMA Local Mitigation Plan Review Crosswalk. Impacts are divided into two categories: Direct Impacts This describes the short-term consequences to people and property which occur directly as a result from the hazard. Indirect Impacts This describes the short-term and long-term consequences, including social and economic impacts. Secondary hazards are also examined here. Because indirect impacts are much broader and difficult to quantify than direct impacts, the section is abbreviated where appropriate to maintain mitigation focus. Impact Magnitude and Severity Summary This subsection summarizes the qualitative magnitude and severity of a hazard based on previous occurrences and the potential direct and indirect impacts. For most hazards the impacts are based on the event of record, or estimated worst case if history of events is limited. Impact magnitude and severity are classified in the following manner: Dane County 4.12

13 Minor: Less than 5 percent of property is severely damaged; facilities and services are inoperable or closed for less than 24 hours. Minor agricultural losses. No fatalities and injuries/illnesses are treatable with first aid Moderate: 5 to10 percent of property severely damaged, and/or facilities are inoperable or closed for more than a week percent agricultural losses. Fatalities possible but most injuries/illnesses are treatable and do not result in permanent disability. Minor indirect impacts. Critical: 10 to 25 percent of property severely damaged, and/or facilities are inoperable or closed for at least two weeks percent agricultural losses. Injuries and/or illnesses result in permanent disability and some fatalities. Moderate indirect impacts. Catastrophic: More than 25 percent of property severely damaged, and/or facilities are inoperable or closed for more than 30 days. More than 50 percent agricultural losses. Multiple fatalities and injuries. Critical indirect impacts. Vulnerability Assessment This section provides an analysis of the exposed properties, people and resources in the county specific to the hazard. This section fulfills Sections 7, 8, and 9 Element A of the FEMA Local Mitigation Plan Review Crosswalk. For clarification and ease of mitigation planning, exposures are broken into four major categories: Population General Property Essential Infrastructure, Facilities, and Other Important Community Assets Natural, Historic and Cultural Resources These assessments draw on the countywide data collected in Section 4.3 Vulnerability Summary. Estimating Potential Losses and Development Trends Assessment This section provides an estimate of the potential losses to the county, and assesses the impact of development trends on future losses. The section fulfills Section 9 Element B and Section 10 of the FEMA Local Mitigation Plan Review Crosswalk. Estimating Potential Losses Potential losses are determined based on available data, so the methodology varies by hazard. For some hazards this may be based on average annualized losses, or using the documented event of record for the hazard and identifying the corresponding damage in dollars, adjusting them for inflation to reflect 2008 costs. Where the hazard occurs in a specific area, such as flood, GIS methods were used estimate losses to structures and critical facilities, as available data permitted. Development Trends Assessment This sub-section examines projected growth trends, based on recent census estimates and development trends as indicated in the most current version of the comprehensive plan. This growth potential is compared against the existing hazard data to estimate how much additional damage the county may expect if growth patterns continue. Dane County 4.13

14 Overall Risk Summary Overall vulnerability for the hazard is measured in terms of geographic extent, impacts, magnitude and severity, probability of occurrence, and exposure. These findings are summarized in this section and analyzed to reveal an overall risk rating for the hazard. This rating is calculated by averaging the numeric ratings for each measurement and then assigning a corresponding interpretation to the average. This determines the vulnerability of the County to the hazard, relative to the other hazards profiled. This corresponds to Section 7 Element A of the FEMA Local Mitigation Plan Review Crosswalk. The interpretive ratings are as follows Low: Minor risk (0 to 1.9 average) Medium: Moderate risk (2.0 to 2.9 average) High: High risk. (3.0 or higher average) Dam Failure Description 2 A dam is a barrier constructed across a watercourse in order to store, control, or divert water. Dams are usually constructed of earth, rock, concrete, or mine tailings. The water impounded behind a dam is referred to as the reservoir and is measured in acre-feet, with one acre-foot being the volume of water that covers one acre of land to a depth of one foot. Due to topography, even a small dam may have a reservoir containing many acre-feet of water. Dams serve many purposes, including agricultural uses; providing recreation areas; electrical power generation; and erosion, water level, and flood control. A dam failure is the collapse, breach, or other failure of a dam that causes downstream flooding. Dam failures may result from natural events, human-caused events, or a combination thereof. Due to the lack of advance warning, failures resulting from natural events, such as hurricanes, earthquakes, or landslides, may be particularly severe. Prolonged rainfall that produces flooding is the most common cause of dam failure. Dam failures usually occur when the spillway capacity is inadequate and water overtops the dam or when internal erosion through the dam foundation occurs (also known as piping). If internal erosion or overtopping cause a full structural breach, a high-velocity, debris-laden wall of water is released and rushes downstream, damaging or destroying whatever is in its path. Dam failures may result from one or more of the following: Prolonged periods of rainfall and flooding (the cause of most failures) Inadequate spillway capacity which causes excess overtopping flows Internal erosion due to embankment or foundation leakage or piping Improper maintenance Improper design Negligent operation Failure of upstream dams Landslides into reservoirs High winds (leading to wave erosion). 2 Wisconsin Emergency Management State Hazard Mitigation Plan Available online at ftp://doaftp04.doa.state.wi.us/wem/hazard_mitigation_plan/index.htm last accessed February 27, Dane County 4.14

15 For emergency planning purposes, dam failures are categorized as either rainy day or sunny day failures. Rainy day failures involve periods of excessive precipitation leading to an unusually high runoff. This high runoff increases the reservoir of the dam and, if not controlled, the overtopping of the dam or excessive water pressure can lead to dam failure. Normal storm events can also lead to rainy day failures if water outlets are plugged with debris or otherwise made inoperable. Sunny day failures occur due to poor dam maintenance, damage/obstruction of outlet systems, or vandalism. This is the worst type of failure and can be catastrophic because the breach is unexpected and there may be insufficient time to properly warn downstream residents. The Wisconsin Department of Natural Resources (DNR) assigns hazard ratings to large dams within the State. Two factors are considered when assigning hazard ratings: existing land use and land use controls (zoning) downstream of the dam. Dams are classified in three categories that identify the potential hazard to life and property: High hazard indicates that a failure would most probably result in the loss of life Significant hazard indicates a failure could result in appreciable property damage Low hazard exists where failure would result in only minimal property damage and loss of life is unlikely. Wisconsin has approximately 3,800 dams, many of which were constructed before Some dams originally used for logging or milling operations are no longer used for their original purpose. An additional 700 dams were built but have subsequently washed out and no longer exist. Approximately 100 dams have been removed since The Federal Government has jurisdiction over large dams that produce hydroelectricity (approximately 5 percent of the dams in Wisconsin). Private individuals or former companies own approximately 60 percent of the dams in Wisconsin. The State owns 9 percent, municipalities such as townships or county governments own 17 percent, and 14 percent are owned by various other groups. A dam with a structural height of over 6 feet and impounding 50 acre-feet or more, or having a structural height of 25 feet or more and impounding more than 15 acre-feet, is classified as a large dam. There are approximately 1,160 large dams in the State of Wisconsin. The Wisconsin Department of Natural Resources regulates all dams on waterways to some degree. However, the majority of dams in Wisconsin are small and not stringently regulated for safety purposes. Figure 4.2 shows the dams in and around Dane County. Dane County has 50 regulated dams. Those that have an estimated hazard class rating of high or significant are represented in Table 4.5. Stewart Lake Dam is rated as a high hazard dam and Dunkirk Millpond is rated as a significant hazard dam, while two others are rated as low hazard. According to the HMPC, Stewart Lake has had some mitigation recently that should reduce its hazard classification. An additional two dams are estimated to be high hazard, and four are classified as significant hazard dams. The Prairie du Sac dam located just outside the northwest corner of the County could potentially have a large impact in Dane County if a failure were to occur. Figure 4.2 shows the extent of inundation from a sunny day failure of this dam, which is also similar in extent to the 100 year floodplain on the Wisconsin River in this area of the County. The County has Emergency Action Plans for this dam as well as Stewart Lake, Babcock and Tenney Park Lock and Dam. One of the issues discovered during the planning process is the high number of dams with an estimated or unknown hazard class. Additional research is needed in this regard. Dane County 4.15

16 Table 4.5 Dams in or Affecting Dane County Dam Name/Impound Estimated Hazard Rating Hazard Rating Max Storage (acre ft) Height (ft) Owner City Owner Organization Stream Mt Horeb Dam/ Stewart Lake High* High* Dane County Dane County Moen Creek Stoughton Dam/ Stoughton Millpond High Stoughton Mazomanie Dam High Mazomanie Prairie Du Sac Dam/ Lake Wisconsin High - 193, Prairie Du Sac Dunkirk Dam/ Dunkirk Millpond Significant Significant Stoughton Marshall Dam/ Marshall Millpond Significant Marshall City of Stoughton Village of Mazomanie Alliant Power Corporation Dunkirk Dam Lake District Blaschka and Son Milling Rockdale Dam/ Rockdale Millpond Significant Cambridge - Yahara River Black Earth Creek Wisconsin River Yahara River Maunesha River Koshkonong River Tenney Park Lock Dam/Lake Mendota Significant - 160, Dane County Dane County Yahara River Source: Wisconsin Department of Natural Resources; *Recently mitigated, designation may change. Geographic Extent Based on the location and hazard ratings of regulated dams in Dane County, the potentially impacted area due to a dam failure is less than 50 percent of the total area of the County, but it is probably more than 10 percent. Therefore, the geographic extent rating is significant. Previous Occurrences There are no documented occurrences of dam failures in Dane County. However, in June of 2008, Lake Delton in neighboring Sauk County overflowed, destroying four homes in the process. Dane County 4.16

17 Figure 4.2 Dams in and Around Dane County Dane County 4.17

18 Probability of Future Occurrences It is difficult to calculate a probability for dam failures because there are no documented occurrences of past events in Dane County, though the potential does exist. Due to the 2008 failure of Lake Delton in neighboring Sauk County the chance of occurrence is assigned an occasional rating (Between 1 and 10 percent chance of occurrence in the next year, or has a recurrence interval of 11 to 100 years). Impact Assessment Direct Impacts Direct impacts are rated based on the actual affect of a dam failure on the category being evaluated. Dam failures can result in extensive downstream impacts, similar to floods, but typically are more devastating due to the high velocities often associated with the events. Populations can be more severely impacted if there is not adequate warning and evacuation time. Indirect Impacts Indirect impacts examine those costs which are associated with, but not directly caused by, dam failures. For example, the evacuation of nursing homes which are affected by a power outage caused by the failure of a hydroelectric dam, is considered an indirect impact. Since very little data is collected on these indirect impacts it is difficult to make a statistical estimation of severity. Impact Magnitude and Severity Summary Without previous data to assess damages and losses or dam failure inundation maps, it is difficult to predict the magnitude and severity of this hazard on the County. However, because there are seven dams rated or estimated to be significant and high hazard dams within the County, and an additional neighboring dam that is rated as a high hazard, a magnitude severity rating of moderate is assigned. Vulnerability Assessment Population Based on current data and current dam hazard classifications in Dane County, there is limited data on which to assess the populations vulnerable to dam failures. Overall, the vulnerability of populations is estimated to be low. Approximately 70 residential parcels may be vulnerable to failure on the Prairie Du Sac Dam. Using the average household size for Dane County, an estimated 170 persons could be vulnerable to failure of this dam. An inundation mapping and analysis study of Tenny Park Dam was underway at the time of this plan s writing, but the results were not available. General Property Based on the limited number of high and significant hazard dams the overall vulnerability rating on general property is estimated to be moderate. Approximately 70 residential parcels may be impacted by Prairie Du Sac Dam. Dane County 4.18

19 Essential Infrastructure, Facilities, and Other Important Community Assets There is one airport and a facility with hazardous materials in the Prairie Du Sac 100-year and 500-year flood hazard zone that could potentially be impacted by a dam failure. The overall impact on essential infrastructure is low. Natural, Historic and Cultural Resources Based on current data and current dam hazard classifications in Dane County, there are no anticipated vulnerable natural, historic or cultural resources. The overall impact of the event on these resources is low. Estimating Potential Losses and Development Trends Assessment Potential Loss Estimates Without GIS-based dam failure inundation maps, quantifiable potential loss estimates are difficult to ascertain. There is one high-hazard dam that drains into Dane County - Prairie Du Sac - that has a mapped flood hazard (based on DFIRM mapping) below it on the Wisconsin River. Assuming the inundation zone would be similar to the 500-year flood, an estimated 364 developed parcels could be impacted. The total improved value is $15,441,400. Assuming 50 percent additional value for contents, the total value of property at risk equals $23,162,100. Many of these parcels are manufactured homes, which would be vulnerable to high velocity flows from a dam failure event, so losses could be as high as 100 percent of this value. The majority of these impacts would be to the Town of Mazomanie (not a participant), and some to the Town of Roxbury. Development Trends Hazard classifications for dams may change if new development near the dam could place people or structures at risk in the event of a failure. Development below the existing low hazard dams in the County should be carefully considered. There are no trends that indicate that this development is occurring. Overall Risk Summary Dam failures present a low risk for Dane County. The events occur infrequently, and the number of known high and significant hazard dams is low; one high hazard dam has recently been decommissioned. The ability to quantify dam failure impacts is difficult without further dam inundation studies and risk analyses. A number of dams within the County need to be assessed for their hazard rating. Depending on these future assessments, the rating for this hazard could increase in the future. Table 4.6 provides the summary for how all aspects of the hazard profile were evaluated to establish an overall hazard rating. This overall rating is compared to the other hazards in Section 4.3 Risk Analysis Summary. Dane County 4.19

20 Table 4.6. Overall Risk for Dam Failure Measurement Rating Value Geographic Extent Significant 3 Probability of Future Occurrence Unlikely 1 Vulnerability Assessment Low 1 Impact Magnitude and Severity Moderate 2 Overall Risk Rating Low Drought Description There are a number of different ways to define drought. Generally, drought is a water shortage caused by a reduction in the amount of precipitation received over an extended period of time, usually a season or more in length. This deficiency results in a water shortage for some activity, group, agricultural or environmental sector. The effects of a drought are aggravated by other factors such as high temperatures, high winds or low relative humidity. The severity of the impact of a drought depends on the duration, intensity, and geographic extent of the event, plus the regional demands on the water supply driven by human activities. Drought is one of the most complex natural hazards because it is not a distinct event with a clearly defined beginning or end. It differs from other natural hazards in that it has an unusually slow onset, may affect multiple jurisdictions or counties simultaneously, and typically causes no structural damage. The effects impact various sectors in different ways and with varying intensity. Categories of Drought Droughts are categorized into four groups based on the severity and impact of the occurrence and measured by the industries affected. These categories are meteorological, hydrological, agricultural, and socioeconomic. It is possible for these conditions to exist simultaneously. A Meteorological drought is the traditional conceptualization of a drought, and is defined solely on the basis of the degree of dryness. This is expressed as a relationship between actual precipitation and the expected average or normal amount, using a monthly, seasonal, or annual time scale. A meteorological drought considers only the physical attributes of the event and not the impact on social or environmental systems. 3 Hydrological droughts examine the effects of precipitation shortfalls (including snowfall) on surface or subsurface water supply (e.g., stream flow, reservoir and lake levels, ground water). The frequency and severity of hydrological drought is often defined on a watershed or river basin scale. Hydrologists examine how these events impact the entire hydrologic 3 National Drought Mitigation Center, What is Drought? Understanding and Defining Drought updated Available online at Last accessed January 8, Dane County 4.20

21 system. Hydrological droughts are usually out of phase with or lag behind the occurrence of meteorological and agricultural droughts. It takes longer for precipitation deficiencies to appear in components of the hydrological system such as soil moisture, stream flow, and ground water and reservoir levels than in other systems. As a result, the impacts of a hydrological drought are also out of phase with drought measurements in other economic sectors. For example, a precipitation deficiency may result in a rapid depletion of soil moisture that is almost immediately discernible to agriculturalists, but the impact of this deficiency on lake and stream levels may not affect fisheries or recreational uses for many months. 4 Agricultural drought links various characteristics of meteorological and or hydrological drought to agricultural impacts. This view of drought focuses on precipitation shortages, differences between actual and potential evapotranspiration, soil water deficits, reduced groundwater or reservoir levels, and the relative effects on agricultural production. Since plant water demand depends on prevailing weather conditions, biological characteristics of the specific plant, its stage of growth, and the physical and biological properties of the soil, agricultural drought accounts for the variable susceptibility of crops during different stages of crop development from emergence to maturity. 5 Socioeconomic definitions of drought associate the supply and demand of economic goods with elements of meteorological, hydrological, and agricultural drought. The supply of many economic goods such as water, forage, food grains, fish, and hydroelectric power depend on weather conditions. The natural variability of climate means that water supply is ample in some years but insufficient for human and environmental needs in other years. Socioeconomic drought occurs when the demand for an economic good exceeds supply as a result of a weather-related shortfall in water supply. 6 Measuring Drought There are numerous ways to measure the meteorological intensity of drought. Examples of some of the more common indices include percent of normal precipitation, the Palmer Drought Index (PDI), the Standardized Precipitation Index (SPI), and the Surface Water Supply Index (SWSI). For the purposes of this plan, The Palmer Index is used because it is the most effective in determining long-term drought (a matter of several months) and is commonly used by the Federal Governments when measuring drought and determining drought-based aid eligibility. The Palmer Index is a measurement only of meteorological drought. The Palmer Drought Index uses temperature and rainfall information to determine dryness or wetness over a period of time. The index is based on the supply-and-demand concept of the water balance equation, which takes into account not only the precipitation deficit at a specific location, but the water content of the soil as well. The values generated for the Palmer Index generally range from 6.0 to +6.0, with negative values indicating drier conditions and positive values indicating wetter conditions. A value range of -/+0.5 indicates normal conditions, while values greater than +4.0 or 4.0 indicate periods of extreme wetness or extreme drought, respectively. The advantage of the Palmer Index is that it is standardized to local climate, so it can be applied to any part of the country to demonstrate relative drought or rainfall conditions. 4 Ibid. 5 Ibid. 6 National Drought Mitigation Center, What is Drought? Understanding and Defining Drought. Dane County 4.21

22 The limitation is that it is not useful for short-term forecasts, and is not particularly useful in calculating supplies of water locked up in snow. 7 Geographic Extent Drought is a regional phenomenon and affects the entirety of Dane County relatively simultaneously. The geographic extent rating is considered extensive. Previous Occurrences Figure 4.3 shows the average Palmer Index values from 1985 to Dane County has experienced Palmer Index values that would indicate extreme drought five times: 1930, 1933, 1938, 1962, and This graph takes into consideration all months of the year. Because agricultural drought is a major concern in Dane County, average Palmer Index values are also represented for the growing season in Dane County (May-September) in Figure 4.4. Generally, Wisconsin experiences low quantities of precipitation accumulation in the winter months. This alone is not a problem, because demand for water is lowest during this time. However, drought in the summer months can cause financial loss or ruin for the agricultural and recreational sectors as the demand for water increases and the shortfalls become apparent. Figure 4.3 Average Palmer Index for Dane County 7 National Drought Mitigation Center, What is Drought? Drought Indices updated Available online at Last accessed January 8, Dane County 4.22

23 Source: Midwest Regional Climate Center, University of Illinois The Hazard Analysis for the State of Wisconsin developed by Wisconsin Emergency Management in 2002 describes the occurrence and impact of drought on the state level. This plan relies heavily on state level data regarding past events and the following description is taken directly from the state hazard analysis: Droughts, both agricultural and hydrologic, are relatively common in the state. Small droughts of shortened duration have occurred at an interval of about every ten years since the 1930's. Extended, widespread droughts have been infrequent in Wisconsin. The five most significant droughts, in terms of severity and duration, are: , , , and These droughts, along with the more recent occurrences in and stretching over the summer of 2005, are profiled below. The selections are drawn from the National Climatic Data Center (NCDC) database. In more recent years, the NCDC has been tracking drought conditions and their consequences in greater detail. Where possible, these accounts are edited and annotated to reflect primarily Dane County information. 9 Figure 4.4 Average Palmer Index for Dane County: Growing Season Palmer Index Value Years Source: Midwest Regional Climate Center, University of Illinois 8 Wisconsin Emergency Management, Hazard Analysis for the State of Wisconsin, November 2002, p National Climactic Data Center, Storm Events, limited to Dane County, Wisconsin. Available online at last accessed January 8, Dane County 4.23

24 The drought was probably the most significant in Wisconsin history considering both the event s duration and severity. This drought had at least a 75-year recurrence interval in most of the State and over 100-year recurrence interval in certain areas. The austere economic aspects of the Depression compounded its effects. The drought continued with somewhat decreased effect until the early 1940s in some parts of the state The drought that occurred during was most significant in the northern part of the state. In the most severely affected areas, the drought had a recurrence interval of greater than 70 years The drought of had a recurrence interval of between 30 and 70 years in all but the northwestern corner of Wisconsin The drought looks like it had its start in 1962 when Dance County received only inches of rain at Truax Field had inches and 1964 had inches of rain. Normal yearly precipitation for is inches The drought of was most severe in a wide band stretching from north to south across the state. Stream flow measuring stations recorded recurrence intervals from 10 to 30 years. Agricultural losses during this drought were estimated at $624 million. Sixty-four counties were declared federal drought areas and deemed eligible for assistance under the Disaster Relief Act. Additionally, numerous private and municipal wells went dry. Federal assistance was used to help communities drill new wells and obtain new water supplies Some believe the drought of was the most severe ever experienced in Wisconsin and much of the Midwest. It was characterized not only by below normal precipitation, but also by persistent dry air and above normal temperatures. Stream flow measuring stations indicated a recurrence interval of between 75 and 100 years. The effects were most severe in north-central and northeastern Wisconsin. The drought occurred early in the growing season and resulted in a percent crop loss, with agricultural losses estimated at $1.3 billion. Fifty-two percent of the state's 81,000 farms were estimated to have crop losses of 50 percent or more, with 14 percent estimated having losses of 70 percent or more. A combination of state and federal drought assistance programs helped the state's farmers recover a portion of their losses. All Wisconsin counties were designated eligible for drought assistance. The effect of this drought on municipal and private water supplies was not as severe as in , with only a few reports of individual wells drying up. A number of municipal water utilities experienced maximum use of their water delivery systems. Many water utilities imposed some type of water-use reduction rules or restrictions, usually involving the limitation of lawn sprinkling and yard watering. Dane County 4.24

25 This drought extended during the summers of 2002 and 2003 over south central and southeast Wisconsin. Many farmers saw their corn crops wither and there were reports that soybeans stopped growing or the pods stopped filling. Alfalfa hay cutting also suffered. Grass growth slowed dramatically, or stopped altogether. Most locations received less than 1 inch of rain for the first 11 days of August. Madison's Truax Field only measured.61 inches of rain, all of which fell on a single day. Newspaper reports indicated that agricultural experts expected the corn crop yield at harvest time in the fall to be 1/2 to 2/3 of normal, and the outlook for soybeans was worse. Sweet corn yields were expected to be 20 to 30 percent below normal. Some farmers reported that their wheat crop died. Large cracks developed in many fields and the grasshopper populations were above normal. In addition, flowage on most rivers and streams was only 15 to 25 percent of normal for early August. Only 0.87 inch of rain fell during August 2003 at Truax Field. Both the Milwaukee and Madison August monthly rainfall totals were 3.46 inches below normal. Conditions continued through the month of October 2003 across south-central and southeast Wisconsin. The entire area was in a moderate (D1) to severe drought (D2) status during the month of October. The monthly rainfall at Madison's Truax Field was 1.60 inches, or 0.58 below normal. Only 5 days received 0.10 inches or more of precipitation. Water levels in lakes, rivers, and streams remained below normal for the entire month, and at some spots they were near record-low levels. Newspaper reports indicated that some farmers didn't harvest much of anything in October Drought conditions developed over south-central and southeast Wisconsin in July 2005, after the weather pattern turned quiet in mid and late June The drought classification for south-central and southeast Wisconsin worsened from D0 at the start of the month to severe drought (D2) on July 19, with the exception of the southeast corner consisting of Walworth, Racine, and Kenosha counties. The drought in these three counties worsened to extreme (D3) on July 19th. The drought was preceded by a long period of below-normal precipitation extending back to March Madison's Truax Field (Dane Co.) reported a 4.08 inch deficit from the beginning of March through the end of July. A warm and dry August helped strengthen the drought. Rainfall deficits for August ranged from between 2.50 to 3.50 inches across the area. At Madison's Truax Field (Dane Co.), a 3.11 inch deficit was reported in August, setting the March through August deficit at 7.19 inches. Most of the precipitation observed occurred during the middle of the month, helping to relieve the drought status for the southeast corner of the state toward the end of August. The remainder of south-central and southeast Wisconsin remained in severe drought status (D2). Drought conditions, both agricultural and hydrological, persisted through October over south-central and southeast Wisconsin. Most of south-central and southeast Wisconsin received less than 1 inch of rainfall (normal monthly rainfall is 2 to 2.5 inches) with monthly temperatures averaging about 2 to 3 degrees above normal. Consequently, the drought conditions didn't improve during the month. The drought rating at the end of the month was D2 (severe) in those counties along and south of a line from Madison to Milwaukee. D3 (extreme drought) conditions existed just south of the Wisconsin-Illinois border. D1 (severe drought) conditions existed over those counties north of a line from Madison to Milwaukee. Newspaper and weather reports indicated that due to the spotty nature of the justcompleted warm-season convective showers, soil moisture conditions varied greatly across Dane County 4.25

26 individual counties, resulting in varying yields. Harvest reports indicated that overall corn and soybean yields didn't suffer as much as originally expected in July. Undoubtedly there were monetary crop losses due to the drought; however estimations were unavailable from county/state agricultural agencies. Drought conditions continued across south-central and southeast Wisconsin through November, but did show improvement by the end of the month due to above normal precipitation. Probability of Future Occurrences Historical data indicates that drought occurs approximately once every five years in Dane County. Using the formula established in Section Profile Methodology, the assessment reflects (15 drought incidents over [divide by] 72 years) x 100 = 20 percent chance of occurrence and a likely occurrence rating. Impact Assessment Direct Dane County is most vulnerable to agricultural drought. Obvious impacts include the losses associated with crop and livestock yields. Dane County is also vulnerable to hydrological drought. Hydrological impacts of a prolonged drought include lower water levels in the lakes and ponds of the County, reduced stream flow, degradation or loss of wetlands, decreased water quality, and lowering of the water table. Indirect The indirect impacts of drought are far reaching. The cascading effects of drought provide a more accurate picture of the drought s affect on the region and the nation. Unlike many other natural hazards, drought may extend indefinitely, but as with all disasters, the more prolonged the event, the greater the damage and indirect impacts. Less obvious impacts of agricultural drought include increased incidents of insect infestation, plant disease and wind erosion. These problems also impact forests and other wild areas, which can reduce levels of growth or result in large areas of dangerously dry vegetation, which in turn increases the risks for wildfires. The incidence of forest and grassland fires increases substantially during extended droughts. In addition, the loss of vegetation and drying and hardening of the ground can result in flooding, even from average rainfall, as rainwater is unable to soak into the soil. The National Drought Mitigation Center (NDMC) at the University of Nebraska-Lincoln suggests examining indirect impacts of drought using three broad categories: economic, environmental, and social impacts. In Dane County, most economic impacts occur in agriculture and recreational sectors because these sectors rely on water supply and quality. The resulting income loss from these sectors creates ripples which impact a wide range of other aspects in the local economy. Retailers that supply these industries also face reduced business which in turn impacts suppliers and production levels. This loss of product turnover may lead to unemployment, increased credit risk, loss of tax revenue, and other economic considerations. Depending on the severity, geographic extent and duration of a drought, every sector of a local economy could experience indirect social and economic impacts. Specific examples include: Agricultural Production Reduced yields and crop loss due to water stress, insect infestation, and plant disease. Dane County 4.26

27 Increased irrigation cost for crops. Reduced productivity of pastureland. Increased feed costs. Reduced milk production. High livestock mortality rates. Disruption of livestock reproduction cycles. Wind and water erosion of exposed topsoil. Cost of new or supplemental water supply. Income loss. Recreation and Tourism Damage to fish habitat and/or reduction of fish populations. Income loss to manufacturers, suppliers, and retailers of recreational equipment, particularly fishing and boating equipment. Water Utilities Increased costs for development of new water sources e.g., cost to drill new, deeper wells. Residential Direct loss of trees, especially young ones. Increased susceptibility of trees to wind damage. Increased risk of wildfire in rural areas. General Economic losses to businesses directly dependent on agricultural production e.g., farm cooperatives, food processors, and dairies. Unemployment from drought-related declines in production. Revenue losses to state, and local governments. Fewer agricultural producers due to bankruptcies or cessation of farming operations. Conversion of farmland to suburban development. Increased demand on disaster assistance programs. Increase in food prices. Impact Magnitude and Severity Summary The severity of drought impacts to the county depends on the type of drought. Agricultural drought, for example, will affect rural and farming communities more severely than urban communities. Socio-economic drought will impact the industries most closely tied to water resources more than unrelated industries. Since agriculture is a significant part of the Dane County economy, and the indirect impacts of drought are extensive and long-lasting, the magnitude/severity rating of a drought is considered critical. Vulnerability Assessment The vulnerability of the people, buildings, and economy of Dane County is very difficult to quantify. Typically, structures and people are not directly vulnerable to drought, though secondary or indirect impacts may eventually increase vulnerability ratings. As discussed in the impacts section, the potential impacts for drought are systemic. However, some areas Dane County 4.27

28 are more vulnerable overall than others and, therefore, benefit from adequate mitigation planning and implementation. For Dane County, the agricultural economy is the most vulnerable to drought and will benefit the most from mitigation efforts. Overall, property and people are not highly vulnerable to drought. Economic resources tied to agricultural production are extremely vulnerable to drought, with secondary vulnerabilities attributed to economic income based on recreational use of natural resources. An overall vulnerability rating for drought is medium. Vulnerability to Agricultural Drought Dane County ranks as one of the country s leading agricultural producers. In 2007, the total market value of agricultural products sold in Dane County was about $280 million (see Table 4.7). Table 4.7 Major Agricultural Commodities in Dane County in 2007 Item Quantity Rank Market value of Agricultural Products Sold ($1,000) Total value of agricultural products sold 470,593 1 Value of livestock and poultry 336,187 1 Value of crops including nursery 134,406 1 Top Five Commodities Value of Sales ($1,000) Dairy products 206,247 3 Grains, oilseeds, dry beans and dry peas 109,384 1 Cattle and Calves 46,362 3 Nursery, Greenhouse, Floriculture and sod 13,521 6 Hogs and Pigs 5,031 6 Top Five Commodities Livestock Inventory (number) Cattle and calves 145,460 2 Layers 75,052 9 Pheasants 26,247 9 Hogs and Pigs 21,977 4 Broilers and Other Meat-type Chickens 9,962 9 Top Five Commodities Crop Area (acres) Corn for grain 172,733 1 Forage-land used for all hay and haylage, grass silage, and green chop 76,970 4 Soybeans for beans 71,684 1 Corn for silage 32,780 2 Wheat for grain, all 12,045 7 Source: 2007 Census of Agriculture, Dane County Profile, USDA National Agricultural Statistics Service. Rank is compared to other 71 counties in the state. Dane County 4.28

29 This is the highest overall value in the state, and in the top 2 percent nationwide. This is a 64 percent increase from the 2002 Census. 10 There are approximately 3,331active farms in the County, covering 535,756 acres. The average size of a farm is 161 acres. Overall, the size of farms has decreased 10 percent since the 2002 Agricultural Census, but the number of farms and overall farmland use has increased 15 percent and 4 percent respectively. Crop sales account for 29 percent of market value production, while livestock sales account for 71 percent. This is a 64 percent increase over the 2002 Census. Corn, hay, and soybeans are the major crops grown in the County, accounting for more than 354,000 acres of cropland. In addition to the value of the agricultural products, the costs and values of agricultural processing must be considered. The 2007 Census of Agriculture notes an additional $18.5 million of income for farm-related sources such as rent, custom work, or recreational services. A 1996 study cited in the Dane County Executive s Design Dane report describes that impact as more than $430 million in wages and salary (5.6 percent of the Dane County total), $936 million in value-added income (7.8 percent of the County total) and 18,900 jobs (6.3 percent of the County total). Vulnerability to Socioeconomic Type Drought Socioeconomic drought occurs when the demand for an economic good exceeds supply as a result of a weather-related shortfall in water supply. The greatest potential social impact of drought for Dane County residents is lack of water for household and recreational uses, while the greatest potential economic impacts remain agriculture and recreation-derived income. The Dane County Wisconsin Comprehensive Plan (DCWCP) offers the following observations about water supply for the county: Groundwater supplies nearly all of the water for domestic, commercial and industrial uses in Dane County. Over 60 million gallons per day (mgd) of groundwater is withdrawn and used- about 140 galloons per person per day. Most of this water is returned to surface water after use. Public water supplies account for about 75 percent of total groundwater use. This includes water withdrawn and used in municipal and private systems for residential, industrial, and commercial purposes. Urban areas account for 80 percent of groundwater use. The City of Madison is the largest single consumer, withdrawing over 30 mgd, and accounts for over half of the total use in the County. 11 Thirty-two water utilities supply water to urban service areas, with a total population of approximately 352,000. The remainder of County residents (approximately 60,000 people) obtains water from private wells. The 2000 Census estimates 21,000 private wells are in service for over 55,000 residents. 12 The DCWCP does identify ten plans, projects, or commissions which address water resources. These include state-sponsored plans (the Department of Natural Resources Basin Plan and the Department of Natural Resources Fisheries, Wildlife and Habitat Management Plan for Wisconsin), regional efforts (Dane County Water Quality Plan and the Regional Hydrologic Model and Monitoring Program), and county programs (Lakes and 10 USDA, National Agricultural Statistics Service, 2007 Census of Agriculture. Available online at last accessed March 19, Dane County Wisconsin Comprehensive Plan, p 53, October Dane County Wisconsin Comprehensive Plan, p 53, October 2007 Dane County 4.29

30 Watershed Commission, Shoreland and Wetland Zoning, Floodplain Zoning, Stormwater and Erosion Control, the Dane County Land and Water Resource Management Plan, and the Waterbody Classification and Riparian Management Project). Each of these plans addresses the social impacts of water supply. Drought impacts may be inferred from these resources, and the potential exists to gather greater tangible data in these efforts, which will improve the ability to analyze the impact of drought on the county and help drive mitigation efforts. Estimating Potential Losses and Development Trends Assessment Potential Loss Estimates The level of analysis needed to calculate the potential for future drought losses encompasses a number of subjective variables. To calculate the future impact of agricultural drought, for example, first a unit of impact must be selected. Assuming fiscal loss to farmers is the primary concern, data would then need to be collected regarding the predictions of future crop yields for the year, statistical information based on rainfall-toharvest yields to estimate impact of weather and water on the growth of the crop, predicted crop cost/sales ratios, and then an extrapolation of various scenarios, all of which must be considered for market value of the crop in question, which varies yearly and sometimes seasonally. Accurate prediction of these goods is probably unreliable more than one season in advance. Since droughts are often regional, long-term hazards, this method of analysis does little to implement proactive mitigation efforts. The same is true for estimating socioeconomic losses of drought, which would incorporate all of the previous data plus expected water demand for household and recreational use, models for impact on lake and stream levels, and comparative data to estimate revenue lost by lower utilization of the recreation. Obviously, then, potential future losses are best discussed by patterns of assumption. Given the occurrences of past droughts, it is reasonable to assume that there is real risk of a significant drought for Dane County. A considerable portion of Dane County s economy is reliant on agriculture and is therefore, vulnerable to drought losses. There is, however, no readily available model or data that can be used to quantify that vulnerability. Based on the documented state-wide losses for the drought it is possible to experience a percent loss in crops. Assuming a severe drought will result in a 50 percent loss of crops, this equates to a potential loss of revenue of $67 million, based on 2007 dollars for crop market value. Assuming drought also impacts livestock production and sales, but to a lesser extent, the planning team assumed a 25 percent loss of livestock sales. This estimate equates to a potential loss of revenue of $84 million in livestock sales. Overall, Dane County could lose $151 million in agricultural revenue during a severe drought, or 32 percent of the total agricultural production revenue. Development Trend Assessment The projected growth trends in Dane County will result in increased demand on water for household, commercial and industrial use poses concerns regarding the existing water supply for Dane County. These concerns are addressed in the plans listed above. Protecting existing water supplies is a major component to drought mitigation, and therefore the future growth of the county, and the associated impact on water supplies that will serve as indirect impacts of drought, are already being addressed. As recommended previously, the increased incorporation of drought data collection into these plans will enhance water protection and quality efforts for the county, as well as provide statistical data for a drought risk analysis. Dane County 4.30

31 The Dane County Water Quality Plan notes that although there is a relatively unlimited groundwater supply in the county, it is critically important that the quality of groundwater be protected for these uses. Groundwater is also very important in providing baseflow discharges to wetlands and streams, which support these resources especially during periods of dry weather. 13 The commercial impact on ground water is currently considered a more significant threat to the county s water supply and quality than a prolonged drought, as addressed in the Water Quality Plan and the Comprehensive Plan, but the potential for cascading affects is addressed. The Water Quality plan also notes that the removal of groundwater, and its eventual return to surface water in a different location, can have indirect but serious impacts on local hydrology and water quality conditions. Though this impact is particularly pronounced in urban areas, it potentially threatens the recreational incomes of watersheds dependant on the flow of underground water sources, which may already be depleted during a drought. Groundwater (water-table) has been above normal in 2008 and 2009 due to heavy rains in August, 2007, record snowfalls for the winter season, heavy rains in June, 2008, and above normal snowfall during the winter season. From February, 2006, through February, 2009, there was a surplus of about 26 inches of precipitation at Madison s Truax Field. Well into the 2009 summer one could still see water in some low spots in Dane County farm fields and other lows spots that normally become dry during summers. Overall Risk Summary Overall, Dane County experiences a medium risk from drought. Though occurrences are fairly likely and are geographically widespread, there is no economic or medical data to indicate that droughts have a serious impact on the county in terms of population, essential infrastructure, general property, or cultural and historic resources. Agricultural drought, which has the greatest fiscal impact on the county, is the larger concern. The potential impact on recreation due to drought is high, but again there is no data to indicate a strong correlation between droughts and loss of revenue from water-based recreation. Table 4.8 provides the summary for how all aspects of the hazard profile were evaluated to establish an overall hazard rating. Table 4.8 Overall Risks for Drought Measurement Rating Value Geographic Extent Extensive 4 Probability of Future Occurrence Likely 2 Vulnerability Assessment Medium 2 Impact Magnitude and Severity Critical 3 Overall Risk Rating Medium Dane County Water Quality Plan, 2004, p 31 Dane County 4.31

32 4.2.4 Flood Much of the following hazard profile is the result of incorporating a previous stand alone flood mitigation plan developed by the County in 2003 and adopted in The Dane County Flood Mitigation Plan was incorporated into this multi-hazard mitigation plan during the 2009 update. This profile includes more detail than many of the other hazards, due to the availability of information in the Flood Mitigation Plan and associated extensive analyses of this hazard. In addition it is one of Dane County s most costly, and complex, hazards. Description 14 Flooding is the accumulation of water within a water body (e.g., stream, river, lake, and reservoir) and the overflow of excess water onto adjacent floodplains. Floodplains are lowlands, adjacent to water bodies that are subject to recurring floods. Floods are natural events that are considered hazards only when people and property are affected. Nationwide, hundreds of floods occur each year, making it one of the most common hazards in all 50 states and U.S. territories (FEMA, 1997). There are a number of types of floods in Dane County, including the following: Riverine flooding, including overflow from a river channel, flash floods, ice-jam floods, and dam break floods Local drainage or high groundwater levels Fluctuating lake levels Debris flow The most common type of flooding event is riverine flooding, also known as overbank flooding. Riverine floodplains range from narrow, confined channels in the steep valleys of mountainous and hilly regions, to wide, flat areas in plains and coastal regions. The amount of water in the floodplain is a function of the size and topography of the contributing watershed, the regional and local climate, and land use characteristics. In steep valleys, flooding is usually rapid and deep, but of short duration, while flooding in flat areas is typically slow, relatively shallow, and may last for long periods of time. The cause of flooding in large rivers is typically prolonged periods of rainfall from weather systems covering large areas. These systems may saturate the ground and overload the rivers and reservoirs in numerous smaller basins that drain into larger rivers. Localized weather systems (i.e., thunderstorms), may cause intense rainfall over smaller areas, leading to flooding in smaller rivers and streams. Annual spring floods, due to the melting of snowpack, may affect both large and small rivers and areas. While there is no sharp distinction between riverine floods, flash floods, ice jam floods, and dam-break floods, these types of floods are widely recognized and may be helpful in considering the range of flood risk and appropriate responses: Flash flood is a term in wide use by experts and the general population, but there is no single definition or clear means of distinguishing flash floods from other riverine floods. Flash floods involve a rapid rise in water level, high velocity, and large amounts of debris, which can lead to significant damage that includes the tearing out of trees, undermining of buildings and bridges, and scouring new channels. The intensity of flash flooding is a 14 Wisconsin Emergency Management State Hazard Mitigation Plan 2008 pp 4-14 to Dane County 4.32

33 function of the intensity and duration of rainfall, steepness of the watershed, stream gradients, watershed vegetation, natural and artificial flood storage areas, and configuration of the streambed and floodplain. Dam failure (see Dam failure hazard profile) and ice jams may also lead to flash flooding. Urban areas are increasingly subject to flash flooding due to the removal of vegetation, covering of ground cover with impermeable surfaces, and construction of drainage systems. Ice jam floods are primarily a function of the weather and are most likely to occur where the channel slope naturally decreases, culverts freeze solid, reservoir headwaters, natural channel constructions (e.g., bends and bridges), and along shallows. Local drainage floods may occur outside of recognized drainage channels or delineated floodplains due to a combination of locally heavy precipitation, a lack of infiltration, inadequate facilities for drainage and stormwater conveyance, and increased surface runoff. This type of flooding has not typically been mapped by the NFIP, and the NFIP only requires local governments to impose land use regulations in a mapped floodplain. Such events frequently occur in flat areas, particularly during winter and spring in areas with frozen ground, and also in urbanized areas with large impermeable surfaces. High groundwater flooding is a seasonal occurrence in some areas, but may occur in other areas after prolonged periods of above-average precipitation. Losses associated with local drainage and high water tables are similar to flood, therefore they are not analyzed as a distinct hazard. Dane County s Flood Problems During the development of the initial Flood Hazard Mitigation (2003) a comprehensive assessment of the impacts and problems associated with floods in Dane County was performed using a combination of survey, public meetings, interviews and GIS. The flood mitigation planning committee s analysis revealed that flooding in Dane County is the result of a combination of highly complex factors that can be distinguished by four main categories: contributing influences, resulting impacts, conflicts, and complicating factors. The category of contributing influences can be further broken down into controllable variables and uncontrollable variables. Controllable variables are those that can be adjusted or modified through regulation of human behavior. Uncontrollable variables are those that are difficult if not impossible to manipulate. In describing the flooding problem, the uncontrollable variables are those that describe the natural process and the lay of the land. None of these variables are problematic in themselves, but combined, they provide an accurate portrayal of where and what kinds of problems are likely to occur. Even so, these factors only become problematic when structures or developments are located in areas of vulnerability. Likewise, none of the controllable variables are problematic unless the uncontrollable variables indicate a risk if a certain use or practice is instituted at a certain site or location. The controllable variables can be adjusted depending on the conditions presented or likely to be presented by the uncontrollable conditions. Contributing influences to flooding in the County include: Controllable land use; zoning regulations; erosion control management practices; building codes; education; Dane County 4.33

34 amount of impervious surfaces; general engineering practices; loss of wetlands; insufficient capacity for stormwater; debris in streams; and development in high-risk areas. Uncontrollable soil type; local topography; depth of the water table; floodplains; weather events; and climate change. Resulting impacts of flooding include: residential and commercial flooding; flooded basements; sewer backups; structural damage to buildings; damage to the contents of buildings. road, shoulder and ditch washouts; crop loss;and health and safety concerns. Each of these categories comes into focus depending on the scale of the analysis. Generally, contributing influences are associated with a regional perspective, and resulting impacts are associated with a site-specific perspective on the flooding problem. Defining the problem in purely physical terms (watersheds, land use, rivers, homes, roads, crops) is not sufficient to completely understanding the flooding problem in the County. Political, social, governmental, and environmental conditions or positions frame and define the problem. Some of the conflicts and complicating factors recognized in this process are: Conflicts: Cognitive Conflicts (Search for the truth) hydrologic systems are dynamic systems, regulations treat them as static systems; varying levels of public awareness; interrelatedness of flooding with many other variables makes an objective comprehension of problem difficult; low levels of communication and cooperation across borders distort reality. Distributional Conflicts (Search for what is acceptable) uneven regulatory field for local units of government; discrepancy in need and desire for County intervention; desire for a quick, local solution to a complex, regional problem; differing social expectations for lake level and waterway aesthetic and function; discernment of the appropriate party to solve the problem. Value Conflicts (Search for what is good varying and conflicting economic, social, and environmental values; distrust of higher levels of government. Complicating Factors: Dane County 4.34

35 high level of regulatory complexity; roles for programs and government departments are unclear. Contributing Influences The survey and assessment of past flood events shows that there is a wide range of factors that contribute to flooding problems. Dane County is primarily a drainage area. The County fully or nearly fully contains the headwaters of most of the rivers and streams that flow through and out of the County. While there are predictors of where floods will occur and the impacts that will result, Dane County does not have a major river and associated floodplain system that can be used to predict a damage potential given a certain probability flood. There are exceptions such as Black Earth Creek and Koshkonong Creek where flooding does typically occur as riverine flooding of a well-defined floodplain. The Yahara River and chain of lakes is another such exception. Flooding around the chain of lakes is not typical riverine flooding, however, the impact of flooding can be readily predicted given lake level elevations. Development in Flood-prone Areas (Areas with inherent flood risk) There are areas of the County that if developed, have an inherent risk of flooding and resulting flood damage. These typically are areas that in their natural state, are associated with floodplains, low lying shorelands, wetlands (existing or drained) and steep slopes with highly erodible soils. Floodplains Developing and building in areas with a natural flood risk is a well-documented cause of subsequent flood damages. The floodplain is very simply the land that has been or may be covered by floodwater during a flood. A cross-sectional view of a typical floodplain is illustrated in Figure 4.5. The 100-year floodplain, 1 percent annual chance flood, Special Flood Hazard Area, and Base Flood are different terms for the same level of flooding, and the level that floodplain regulation in the United States is based upon. The floodway is a zone within the Special Flood Hazard Area that has even stricter regulations, as it is typically where flood flows are highest and deepest. Shallower flooding with slow or no velocity happens in the flood fringe. To build or develop in a floodplain exposes the owner to an inherent risk of flooding at some point in the future. Figure 4.6 shows the location of mapped floodplains. Dane County 4.35

36 Figure 4.5 Floodplain Definition Sketch. Source: FEMA, August The locations and delineation of floodplain boundaries, however, are not static. Floodplains change over time. Though they are represented as a line on a Flood Insurance Rate Map (FIRM), floodplains and flood risk are not black and white. The floodplain maps are designed to indicate areas with a risk of flooding, but those areas are constantly changing. Increasing impervious surface areas with new development, soil saturation, rainfall intensity, stream conditions, shoreland and wetland modifications (both restoration and degradation), and stormwater management practices all affect the extent to which flooding will occur. And these influences are constantly changing as well. The survey identified frequent reports of areas that never flooded in the past, but do flood now. In addition to this, there is a widely held perception that the 100-year floodplains shown on a FIRM represent a clear boundary of flood risk. On one side of the line, there is a flood risk, on the other side, there is not. This is not what the maps are intended to show. Flood risk is a continuous spectrum and the floodplains shown on the FIRM represent but one increment of that spectrum, the 1 percent probability of flooding. For regulatory and insurance purposes, a line has to be drawn somewhere. There is a danger in using this line as the end-all in determining flood risk. The maps are intended to represent the risk as accurately as possible, but they are merely a prediction of the extent of flooding that could occur in the future, based on a snapshot of present and past conditions. Nevertheless, the location of mapped floodplains is a major indicator of where flooding will occur in the County and it is a major indicator of subsequent damages. While the accuracy of FEMA s Flood Insurance Rate Maps (FIRM) has been the subject of much debate, these maps still provide the best information available regarding the location of floodplain boundaries. Hydric Soils Though mapped/regulatory floodplains are a good predictor where flooding occurs, floodplains do not account for all of the flooding in the County. The location of certain soil types, hydric soils in particular, is also a good predicator of where flooding is likely to occur. Dane County 4.36

37 Hydric soils are formed under conditions of saturation, flooding, or ponding long enough during the growing season to develop anaerobic conditions in the upper part. They are a good indicator of the historic locations of wetlands or other wet areas. As such, development in areas with hydric soils is another prime indicator of where flood damages are likely to occur, especially in areas where urbanization has not altered the natural hydrology of the area. Figure 4.6 shows the locations of hydric soils in Dane County. Topography The topography of the County affects the spatial extent of flooding. In the western portion of the County where topography is most exaggerated, flooding occurs in small areas, yet the water flow rate is much higher than in the eastern part of the County. There, landowners experience expansive flooding, since the water is able to stretch across the landscape more easily. This contributes to greater crop loss. Topography and hydric soils are useful indicators of the frequency and extent of flooding outside the floodplain. Impediments to the Flow of Water Changes in stream conditions and impediments to the flow of water were identified as a significant factor in increasing flood problems along the rivers and streams of the County. Impediments to flow reduce the overall capacity of the stream to convey water and cause water to back-up behind the blockage. These impediments include blockages caused by accumulation of sediment, over growth of weedy, non-native vegetation, or excessive debris in the stream channel. Reduced conveyance capacity and blockages can and do occur in all components of the natural and human-made components of the drainage system, including detention ponds, stream channels, drainage ditches and culverts. Debris in the Drainage System Debris in streams has been identified as a significant problem in numerous areas of the County. Debris refers to a wide range of materials that may include tree limbs and branches that may accumulate naturally or garbage and trash that has been dumped into channels or drainage ditches. There is often a very fine line between debris that should be removed to improve conveyance capacity and natural material that is necessary for fish and wildlife habitat. Silt and Sediment Silt and sediment has also been identified as a significant impediment to flow in numerous streams and ditches of the County. Farmlands and construction sites typically contain large areas of exposed soil. Surface water runoff can erode soils from these sites and carry sediment into downstream waterways. Erosion also occurs along streambanks and shorelines as the volume and velocity of flow destabilizes the banks and washes away the soil. Sediment suspended in the water tends to settle out where the flowing water slows down. It can clog storm sewers, culverts, and ditches and reduce the water conveyance capacity of rivers and streams. Not only is the drainage system less able to carry water, but the sediment in the water also reduces light, oxygen, and water quality and often carries agricultural chemicals and other pollutants into the water. Dane County 4.37

38 Figure 4.6 Mapped Floodplains and Hydric Soils in Dane County Dane County 4.38

39 The erosion control elements of the County s Stormwater Management and Erosion Control ordinance are designed to address these issues. Even with the ordinance in place, however, streams that are currently restricted by sediment will remain restricted unless the existing sediment is removed. Human Constructed Impediments to Flow Bridges, culverts, and drainage ditches that are improperly sized have been noted as a significant factor in restricting the flow of water and exacerbating flood problems. This does not appear to be a systematic problem, but rather one that occurs in a few isolated areas of the County. Loss of Wetlands Wetlands are often found in floodplains and low-lying areas of a watershed. Many wetlands receive and store floodwaters, thus peak flows and volumes of floodwaters. Wetlands also serve as a natural filter, which helps to improve water quality. Wetland loss has affected all of Dane County. Wetlands have been tiled and drained to produce fertile farm fields and they have been filled and paved to prepare for development. Wetlands on the Yahara Chain of Lakes have also been lost during recent flood events as rising floodwaters detach and lift sections of marsh. The floating marsh sections have been subsequently removed to eliminate the navigational hazards they posed. Lakes in the Yahara Chain of Lakes have lost between half and nearly all of the wetlands associated with them since Healthy wetlands have the potential to store large volumes of floodwater. As wetlands become destroyed or degraded, their capacity to store water may be reduced. Water that would otherwise have been stored in the wetlands then contributes to increasing flood levels and flows. The maintenance and restoration of wetlands has the potential to be a very effective flood management tool. Upland Development and Stormwater Issues Dane County is among the fastest growing and developing counties in the State of Wisconsin. The challenges of managing this rapid development are wide-ranging; however, one of the more significant impacts is the effect of development on the hydrology of the watershed. The effect of upstream development on downstream properties was widely recognized as significant contributing factor in Dane County s flood problems. In fact, development and other changes to the landscape in areas far outside the floodplain can have a profound impact on the magnitude and frequency of downstream flooding. This is a highly complex issue that includes elements of land-use decision-making, property rights, intergovernmental cooperation (or lack of), as well as the hydrology of the watershed and stormwater management practices. Many of these elements are well beyond the scope and charge of this Plan, however, the issues as related to stormwater management can at least be framed here. The Dane County Board of Supervisors adopted the Erosion Control and Stormwater Management Ordinance effective August 22, 2002, acting on the recommendation of the Dane County Lakes and Watershed Commission after 11 public hearings and hundreds of hours of meetings with citizens, technical experts, developers, builders, local municipalities, and other stakeholders. The Board found that construction site erosion and uncontrolled stormwater runoff from land disturbing and land development activities have significant adverse effects upon regional water resources including the health, safety, property and general welfare of the community, diminishing the public enjoyment and use of natural Dane County 4.39

40 resources. The Board also found that effective erosion control, sediment and stormwater management depends on proper planning, design, timely installation and continued maintenance of erosion control and stormwater management practices. Specifically, they found that soil erosion and stormwater runoff can: carry sediment, nutrients, pathogens, organic matter, heavy metals, toxins and other pollutants to regional lakes, streams and wetlands; diminish the capacity of water resources to support recreational and water supply uses and a natural diversity of plant and animal life; clog existing drainage systems, increasing maintenance problems and costs; cause bank and channel erosion; increase downstream flooding; reduce groundwater recharge, which may diminish stream base flows and lower water levels in regional lakes, ponds and wetlands; contaminate drinking water supplies; increase risk of property damage and personal injury, and; cause damage to agricultural fields and crops. Effective January of 2006, revisions to the erosion control and stormwater management ordinance were made to meet state standards for infiltration and to make shoreland erosion control requirements of Chapter 11 consistent with Chapter 14. More information on the ordinance can be referenced in Section Additional Capabilities. The Effects of Urbanization Urbanization is one of the most severe land use impacts in terms of its lasting effects on hydrology, due to the much higher percentages of impervious or paved areas covering the land. Rural land surfaces are almost completely pervious, while about one-third of the land surface in urban areas is covered by rooftops and paved areas. The main effects of urbanization on the hydrology of an area include: An increase in the total amount of rainfall running off the surface of the land; A decrease in the amount of rainfall infiltrating into the soil; More rapid runoff and much higher peak flows; and Reduced baseflows in streams during dry weather periods. In addition to generating more surface runoff, which erodes the land surface and washes off more pollutants, the hydrologic effects of urbanization have less direct but more important downstream impacts. The increased peak storm runoff rates and reduced base flow associated with urbanization have serious negative impacts on receiving streams, usually resulting in erosion, sedimentation, streambank instability, and flooding. Combined with reduced base flow, the scenic, recreational and habitat values of the receiving streams can be seriously degraded unless a vigorous effort is made to provide management practices and programs to counter the effects of urbanization. Climate Change The earth s climate is predicted to change because human activities are altering the chemical composition of the atmosphere through the buildup of greenhouse gases primarily carbon dioxide, methane, nitrous oxide, and chlorofluorocarbons. The heat trapping property of these greenhouse gases is undisputed. Although there is uncertainty about exactly how the climate will respond to the increased concentrations of greenhouse gases, observations indicate that detectable changes are already occurring. There will most Dane County 4.40

41 likely be increases in temperature and changes in precipitation, soil moisture, and sea level, which will likely have adverse effects on many ecological systems as well as on human health and economy. Water resources are affected by changes in precipitation as well as by temperature, humidity, wind, and sunshine. Because evaporation from streams and lakes is likely to increase with warmer climate, it could result in lower river flow and lower lake levels, particularly in the summer. In addition, there is also a trend toward fewer, but more intense rainfall events, which in turn could lead to both increased droughts and increased flooding. Groundwater supplies could also be reduced if streamflow and lake levels drop. This increasing variability has to be considered in water resource planning for the future. Geographic Extent Flooding is generally a regional phenomenon in Dane County. The impact varies based on geographic location to waterways, soil content and ground cover, and construction. The extent of the damage of flooding ranges from very narrow to widespread based on the type of flooding and other circumstances such as previous rainfall, rate of precipitation accumulation, and time of year. Dane County s mapped floodplains are shown in Figure 4.7. It is considered to have a significant geographic impact rating. Refer to the County profile section of this plan for a thorough description of the County s major drainage basins and associated rivers, streams and lakes. The 2003 flood survey included an assessment of the impacts and problems associated with floods in Dane County. The survey and associated maps describe the causes and effects of flooding as well as the geographical location of each problem. Map and Flood Mitigation Plan Survey data were transposed into a geographical information system (GIS) for further analysis. The results of the process were represented as points on a countywide map. Each point represents an area delineated on a map by a survey respondent and carries with it a unique set of flooding problems recorded by the survey. This area is referred to as a problemshed. The total number of problemsheds recorded through the survey is 184. The land area of the problemsheds range from 100 s of acres to down to a single block. The severity of the problem or problems that a problemshed represents also ranges from severe to minor. Figure 4.7 shows the geographical distribution of the points or problemsheds, within the watersheds of the County. Dane County 4.41

42 Figure 4.7 Watershed and Problemshed Locations Dane County 4.42

43 Figure 4.8: The Distribution of Flood Problem Areas across the County, Based on the Flood Mitigation Plan Survey Locations of Flood Problem Areas Sorted by Watershed 35 Number of Problemsheds W. Branch Sugar Lower Koshkonong Allen & Middle Badfish Gordon Lake Wisconsin Mill and Blue Mounds Maunesha Roxbury Upper Sugar Yahara Kengonsa Yahara Mendota Upper Koshkonong Six Mile & Pheasant Black Earth Yahara Monona Previous Occurrences Dane County received Presidential disaster declarations for widespread flooding seven times since Significant damages were also recorded in Cumulative losses for these disasters exceed $65 million, including private, public and agricultural damages. Damage assessment summaries for those years are shown in Table 4.9. As shown, losses caused by widespread flooding have been substantial. Private and public losses shown as estimated are based on a compilation of local damage assessment figures. Public and private losses shown as actual are based on FEMA public and private assistance program payments. Agricultural losses are based on Dane County UW-Extension and USDA Farm Service Agency (FSA) estimates. Figure 4.9 shows the number of events, deaths and injuries related to flood events for the entire state of Wisconsin from 1982 through Dane County is tied for the fifth most total flood events. Dane County 4.43

44 Table 4.9 Damages from Disaster-Declaration Floods in Dane County ( ) Year Loss Type Amount Year Loss Type Amount Private losses: Not available Private losses: $5.0 million (est.) 1978 Public losses: $180,000 (actual**) 2000 Public losses: $1.1 million (actual) Agricultural: Not available Agricultural: $3.2 million (est.) 1990 Private losses: $30,343 (actual*) Private losses: $3.3 million (est.) $585,000 (actual*) 2007 Public losses: $37,000 (actual**) Public losses: $1.8 million (est.) Agricultural: Not available Agricultural: Not available 1993 Private losses: $11.5 million (est.) Private losses: 2008 Public losses: $1.1 million (actual) Public losses: $7.45 million (est.) $1.75 million (actual*) $6.07 million (est) $1.5 million (actual **) Agricultural: $10 million (est.) Agricultural: Not Available Private losses: $6.8 million (est.) 1996 Public losses: Agricultural: $1.7 million (est.) $2.5 million (est.) Source: Dane County Emergency Management; * Federal Individual Assistance Payout; ** Federal Public Assistance Payout Dane County 4.44

45 Figure 4.9 Total Flood Events for Wisconsin Source: National Weather Service, 2009 A brief description of past flood events, and their impacts are listed below. Accounts prior to 2002 are taken from the 2004 Dane County Flood Mitigation Plan. More recent events are pulled from the National Climactic Data Center Database. Dane County 4.45

46 Spring, 2009 During the 2009 update of this plan flood problems began in early March in some areas of the County, notably the northern portion. Road flooding and some residential flooding was reported in the towns of Vienna and Roxbury. Fish Lake in the Town of Roxbury was threatening residential properties with rising lake levels. Substantial rainfall on still-frozen ground may have been a contributing factor to this flooding. Several roads were underwater and closed around Crystal Lake. 22 Recreational vehicles or other structures at the Crystal Lake RV Resort and Campground were substantially damaged. July 11, 2008 A series of thunderstorms dumped heavy rains of 1 to 3 inches within an hour or two that generated flash flooding. May urban roads were flooded with fast-flowing water of 1 to 2 feet in depth. Basement flooding was noted with damage to contents. A series of thunderstorms developed into clusters and short lines that moved east-southeast through southern Wisconsin. Due to a moist atmosphere, heavy rains were reported overnight in the range of 1 inch to slightly over 4 inches. Due to a saturated ground, flash flooding was the result. June 7, 8, & 12, 2008 Heavy rains resulted in flash flooding as water reached depths of 3 feet or more and several cars stalled. This was the last of 6 flash floods in Dane County on 3 different days. The first one occurred on June 7th, the next two on June 8th, and the last three on June 12th. In all six cases, damage to homes, businesses, and crops was noted. It was nearly impossible to break down the damages by flash flood event. Therefore, the collective breakdown is provided in this last June 12th flash flood StormData entry for Dane County. Some farm fields remained flooded into early July. The breakdown for residential home losses were: 2,020 minimally affected, 248 with minor damage, 109 with major damage, and 3 destroyed (total of $6.797 million). The breakdown for business losses were: 152 with minor damage, and 3 with major damage (total of $677 thousand). Crop losses were estimated at $64.6 million. Public sector damage was about $6.067 million. Several roads and bridges sustained damage. A series of clusters of strong to severe storms ahead of a cold front moved east/northeast across south-central and southeast Wisconsin. Copious amounts of moisture were available that allowed repeated heavy rains. Additionally, there was sufficient vertical wind shear to allow for the generation of supercell thunderstorms with rotating updrafts that led to seven tornadoes in this part of the state of Wisconsin. August 22, 2007 Flash flooding occurred due to repeated thunderstorms with heavy rains on top of a saturated ground. From Madison to Sun Prairie many roads had fast-flowing water depths of 6 inches to 1 foot, and several were closed. Sandbagging also took place to control the flash flooding. A 1-hour rainfall total of 2.26 inches was measured by a spotter in Madison. Soil erosion and crop damage also occurred on several other farms in that area. Additionally, a few basements had water damage to contents. August, 2007, rainfall totals in inches include: at Madison Truax Field, at the UW-Charmany Farm, at Mazomanie, in Middleton, near Mt. Horeb, in Stoughton, in Sun Prairie, and at the UW Arboretum. Up to 20 may have fallen in the southwest corner. During the afternoon and evening hours of August 22nd, the second round of storms for the calendar day moved across south-central and southeast Wisconsin. The clusters or short Dane County 4.46

47 lines of storms moved east at a speed of about 30 knots (35 mph), and generated damaging downburst straight-line winds that toppled trees and power-lines, and heavy rains that triggered flash flooding. Synoptically, a stationary front stretched from northern Iowa to Wisconsin/Illinois border. Warm, moist, unstable air flowed north over the front in association with an upper-level short-wave trough, resulting in thunderstorm generation. Hourly rainfall rates peaked around 2 inches. By the end of August, 2007, many locations in south-central and southeast Wisconsin established new August rainfall records and alltime/any month rainfall records. Many locations measured 10 to over 20 inches for the month of August, 2007, or about 200 percent to over 400 percent of normal. Normal August precipitation in southern Wisconsin is about 4 to 4.25 inches. August 23 and August 24, 2006 A stagnant weather pattern on August 23rd and 24th resulted in waves of heavy rain and severe thunderstorms. A warm front pushed north during the afternoon of August 23rd. A very unstable airmass with moderate shear caused thunderstorms to break out during the afternoon and continue through most of the overnight as a warm front moved north through the area. After a brief respite of only 3 hours during the morning hours of August 24th, more storms developed during the late morning and afternoon hours. More heavy rain, large hail, damaging winds, and vivid lightning resulted from these storms. Urban flooding in Dane and Kenosha counties caused a few hundred thousand dollars in structural damage. Some two-day rainfall totals across Dane County include 5.70 inches in Oregon, 5.38 inches in Cottage Grove, 3.26 inches in Middleton, 2.77 inches at Beloit College, and 2.73 inches at Madison Truax Field. Roughly 12,000 customers lost electrical power due to downed power lines and lightning strikes. July 27, 2006 A 1-in-a-100-year flash flood occurred from the west side of Madison to around the Capitol Square after 3 to 5 inches of rain fell within a 90 minute timeframe. There were no reports of injuries or deaths. The heavy rain resulted from slow-moving and back-building thunderstorms that essentially remained nearly stationary over the city of Madison. The hilly terrain and a typical urban setting of a lot of concrete and asphalt enable the runoff water to quickly overwhelm the storm sewers and concentrate water in low-lying areas of the city. Water depths reach to the top of small vehicles - 4 to 5 feet deep in spots. Many roads became impassable due to the flood waters, and many residential homes and businesses on or near the UW-Madison campus had flooded basement and first-floor flooding. Some basement apartment units had water depths of 6 to 8 feet. Nearly all campus buildings had flooding of varying degrees of intensity, and the Camp Randall football field sustained damage. Some campus buildings had flat roofs that quickly flooded as storm drains became plugged, which allowed water to run through the walls and ceilings of buildings. The buildings that sustained the most damage were the Memorial Union, Computer Sciences, and Veterinary Medicine. Numerous vehicles on or near the campus were damaged or totaled by the flood waters, and some were reported to be floating away. Unofficial rain gages measured 4.5 to 5 inches from just west of West High School up to the Capitol Square. WSR-88D Doppler rainfall estimates were in the 3 to 5 inch rain, therefore it appears the unofficial rain gages were very accurate. Rainfall amounts quickly fell off to 1 to 1.5 inches near the south Beltline. It is nearly impossible to assess the monetary value of the flash flood damage. Dane County 4.47

48 June 9-12, 2004 Scattered, widespread heavy rains across south-central and southeast Wisconsin during this period kept many rivers and streams at or above flood stage for most of the month. Monthly rainfall totals generally ranged from 4 to 7 inches across south-central and southeast Wisconsin. During this time, high water levels submerged most of the bottom-level land near rivers and streams; closed some major state highways; forced water into basements; damaged corn, soy bean, and alfalfa crops; delayed planting of entire fields; washed out gravel road shoulders; and damaged foundations of homes and businesses. In general, the flooding was the worst since 1993 on a widespread basis and locally in the past 25 to 30 years. Federal Disaster Declaration 1526 covered all 20 counties in south-central and southeast Wisconsin for storms, tornadoes, and flooding for the period of May 19-July 3, All counties qualified for "individual assistance". In Dane County, lake levels were 1 to 3 feet above normal. Minor basement flood damage to 127 homes, and major damage to 3 homes, was reported and property damages were estimated at $1 million. Estimated crop losses were $3million started very dry, beginning in the fall of 2000, with all regions of the state below 50 percent of the October precipitation average. Beginning in the winter, precipitation was highly variable and the state went through a series of wet and dry spells. However, by May the central and southern portions of the state had received 160 percent of normal precipitation. After a July dry spell, severe thunderstorms on August 1-2 dumped heavy rain over a large portion of Dane County. Most areas of the County received between 2 and 5 inches of rain. The heaviest rainfall was centered over the northwest portion of Dane County. A credible report to the National Weather Service indicated that an 11-inch capacity rain gage had overflowed in the Village of Black Earth. Flash flooding occurred in the Black Earth Creek with significant impact to the Villages of Black Earth and Mazomanie. Flash flooding also occurred in Roxbury Creek, causing a significant impact on the village area in the Town of Roxbury The month of May 2000 was a particularly wet month in the southern half of the state. Data from the National Weather Service indicates that it was the wettest May ever recorded for most locations in southern Wisconsin, including Dane County. Generally, 8 to 12 inches of precipitation was measured, with some locations in Dane and Iowa Counties unofficially receiving between 16 and 18 inches. Normal rainfall for May is 3.14 inches. Finally, the wet rainy weather culminated in a series of severe thunderstorms and heavy rains that began on May 26 and continued into early June. Those storms dumped nearly 6 inches of rain on already saturated soils. This caused most, if not all of the rainfall to run off instead of infiltrating into the ground. The result pushed most area rivers over flood stage, raised all of the Yahara Lakes to record or near record levels, and caused severe, widespread flooding. Dane County received a presidential disaster declaration and was eligible for public and private assistance programs The County experienced widespread flooding in 1996, largely as a result of a June storm. Over this period of time, heavy rains fell over most of the region of southern Wisconsin. The National Weather Service recorded 5.25 inches of rain in Madison. The Sun Prairie Wastewater Treatment Plant recorded 5.77 inches over this same time period. Lake Dane County 4.48

49 levels of the Yahara Chain of Lakes were within inches of all-time record highs and most rivers and streams were at or above flood stage. The flooding that resulted caused severe problems on agricultural lands as well as in the City of Madison, the City of Monona, the City of Sun Prairie, the Villages of Mazomanie and Black Earth. In the Department of Emergency Management s damage assessment, nearly every local unit of government in the County reported at least some damage to public and private facilities Flooding was also widespread across the County in The flooding in 1993 was a result of above average precipitation for each month from March through August, as recorded by the National Weather Service. The primary significance of the 1993 storm events was not the intensity, but the frequency. Most days during June and July had at least a minor rainfall event. Between June 28 and July 11, there were only two days out of 14 with no rain. There was also one significant individual storm during this time period, a 3.75-inch rainfall event on July 5, This was approximately a 5- to 10-year storm (10 percent to 20 percent annual probability) event. The total precipitation for this 14-day period was 7.86 inches while the average is 1.83 inches. Therefore, during most of June and July, the soils of the County remained saturated and did not have time to dry out between storms. This caused significant crop loss, and the resulting increased runoff raised most area rivers over flood stage and raised all of the Yahara Lakes to record or near record levels. Dane County received a presidential disaster declaration and was eligible for public and private assistance programs. July 1990 Torrential rains and flooding caused an estimated $14 ($18.4) million in damages in 14 counties in southern Wisconsin. In the City of Madison, 12 trees were lost due to high winds, storm sewers backed up, and two homes caught fire due to lightning strikes, one sustaining $50,000 ($65,800) in damages. Several parts of the Military Ridge bicycle and hiking trail were washed out. Also, high water lifted a car off the ground on University Avenue and washed it across a parking lot. Businesses dependent upon water-based recreation lost money having to cancel boat trip due to high waters in rivers. Summer 1980 Heavy rains drenched central Wisconsin and Dane County. August rainfall broke the month s record, setting the bar at 9.49 inches. The National Weather Service issued numerous flash flood warnings. Madison Gas and Electric reported 15 power outages. Two hundred people were affected on Madison s west side and another 200 were affected in the Springfield area. At the same time, more than 2 inches of rain fell in Mount Horeb. Lake Mendota rose 17.5 inches above the normal of 850 feet above sea level. Lake Monona was also above the seasonal average. Media outlets designated southern Wisconsin including Dane County as rain alley. July 1978 Former President Jimmy Carter declared a flooding disaster for 16 southern and western Wisconsin counties Dane included. In July, Wisconsin experienced rainfall that was 75 percent above normal. An estimated $53 ($139.8) million in damage was produced from a series of weekend storms July 8-9. Rain fell heavily throughout the state from May through September, producing a bumper crop for some farmers, but other farmers were not so lucky. In Dane County, about 9,000 acres of cropland on 800 farms were damaged in June Dane County 4.49

50 and early July rains. Crop losses approached $2.1 ($5.5) million on 500 farms; corn and soybean crops were most severely damaged suffering $1.4 ($3.7) million in losses. Tobacco and cabbage losses were estimated at $700,000 ($1.8 million). Floodwater also eroded soil from fields and scattered debris, increasing costs to farmers. Residents in the City of Monona along Lake Monona also flooded Flooding again comes to the Mississippi river as Wisconsin is declared a disaster area as one of 8 states that split $147 ($570) million in Federal aid. Then-governor Lucey estimated private and public damage at almost $2.3 ($8.9) million. Madison broke a 17-year-old, 24- hour rainfall record as streets and sewers flooded. The City of Madison received 25 calls for flooded basements. The hardest hit areas in Madison on the east side included East Washington, and Milwaukee St., on the west side Odana Hills, Crestwood, Meadowood, Park St., and Manitou Way. Streetlights shorted, auto accidents were reported. Rain and debris frustrated street crews. Monona police reported flooding in Maywood Park and stalled motorists on Lake Monona shoreline streets. The federal government began offering funding for repairs due to flooding, but only to those units of government with a flood plain ordinance. Dane County and most incorporated areas did not comply with Federal regulations In 1960, citizens in Dane County were complaining about flooding in Starkweather Creek northeast of Madison, as well as the creek s resident insects and putrid odor. Additionally, basements were flooding and sewers were backing-up in the area and there were calls for dredging of the Creek. 15 High Lake Levels The Yahara Chain of Lakes runs directly through the most urbanized areas of the County. Flooding occurs in low areas surrounding many of the lakes when lake levels rise. Survey data collected indicated that lakeshore flooding is a significant problem, especially in the Yahara River and Lake Monona watershed. High lake levels in the Yahara Chain of Lakes during and after major storms events has affected hundreds of homes, flooding basements or first floors and damaging unimproved property. Total damages to residences along the lakes were by far the highest reported. Historical data shows that the lake levels are becoming more volatile. The lakes were at record or near record high levels for all three of the major flooding events of the past decade. Record levels were set in 1993, broken in 1996, and then broken again in Table 4.10 indicates the levels of the lakes with respect to the base flood elevations shown in FEMA s Flood Insurance Rate Maps for Dane County. 15 Dane County Department of Emergency Management Dane County Flood Mitigation Plan 2004 p 31. Dane County 4.50

51 Table 4.10 Lake Levels in Peak Flood Years Lake Base Flood Elevation Pre-1990 Peak Elevation 1993 Peak Elevation 1996 Peak Elevation 2000 Peak Elevation 2007 Peak Elevation 2008 Peak Elevation Mendota 852 Monona (Set in 1978) (Set in 929) * * Waubesa 847 Unknown * Kegonsa 845 Unknown * * Record high level Source: Dane County Public Works, 2009 FEMA Flood Insurance Rate Maps, Wisconsin State Journal; Source of data is Dane County Land and Water Resources Department lake levels website. The data shown in Table 4.10 highlights an interesting element of the flooding in Dane County. It doesn t take a 100-year rainfall event for the Yahara Lakes to reach the mapped 100-year flood levels. For Dane County, a 100-year rainfall event is defined as 6 inches of rain falling over 24-hours. Peak rainfalls in a single day approached this level in 1996, but the rainfall was much more spread out in the other flood years. Yet in all of these years, the lake levels for all four lakes were very near or above the base flood elevation. This helps to underscore the fact that 100-year rainfall events are different from 100-year flood events. From the perspective of lake level response to storm events, circumstances such as soil saturation and frequency and duration of the rainfall events are as significant as or more significant than 24-hour rain intensity. Flood Insurance Claims There are approximately 65 properties in Dane County on record as having made flood insurance claims between 1978 and Between 2002 and 2008, an additional 123 claims have been paid, for a total of $1,699,049 in flood insurance payments. This number represents a small sample of the actual number of homes impacted by flooding in the County. The majority of these properties are located along the Yahara Chain of Lakes (City of Madison, City of Monona), but also the Village of Oregon and Village of Mazomanie, and City of Edgerton has had claims. Table 4.11 provides more detail on the number of paid flood insurance claims in Dane County since Note that a number of the claims are in the X zone, which is considered to have no or minimal flood potential. Table 4.11 Paid Flood Insurance Claims Community Name FLOOD_ZONE POST_FIRM # of CLAIMS Total Payments Black Earth, Village Of A N 2 $4,969 Black Earth, Village Of A Y 3 $9,754 Black Earth, Village Of X N 1 $262 Cross Plains, Village Of X N 1 $1,724 Dane County A N 30 $836,017 Dane County OTH 1 $7,023 Dane County X N 15 $419,566 Dane County X Y 7 $62,496 De Forest, Village Of X N 1 $7,258 De Forest, Village Of X Y 3 $13,051 Dane County 4.51

52 Community Name FLOOD_ZONE POST_FIRM # of CLAIMS Total Payments Edgerton, City Of A N 5 $67,102 Edgerton, City Of OTH N 2 $3,103 Edgerton, City Of X N 1 $8,077 Madison, City Of A N 3 $9,100 Madison, City Of OTH 1 $649 Madison, City Of X N 9 $46,962 Madison, City Of X Y 2 $16,066 Marshall, Village Of OTH 1 $222 Marshall, Village Of X Y 1 $15,351 Mazomanie, Village Of A N 6 $10,830 Mazomanie, Village Of X N 2 $401 Monona, City Of A N 4 $25,002 Monona, City Of X N 7 $43,229 Oregon, Village Of A N 15 $163,376 Oregon, Village Of A Y 1 $26,221 Oregon, Village Of OTH 1 $6,894 Oregon, Village Of X N 3 $9,798 Sun Prairie, City Of X N 1 $2,964 Waunakee, Village Of X Y 2 $34,220 TOTAL 131 $1,851,689 Source: FEMA; Data as of end of year 2008 Probability of Future Occurrences The studies used to generate the Flood Insurance Rate Maps are based on calculations of the probability of future flooding. Flood studies use data and modeling, as well as historical records to determine the potential for floods of a certain magnitude to occur. Such events are measured by their recurrence interval, e.g., a 25-year flood or a 100-year flood. These terms can be misleading. People often interpret the 100-year flood to mean once every 100 years. This is not correct. The 100-year flood is actually a statistical term that refers to the odds of a flood of that size happening in any given year. This converts to a probability of 1 percent that a flood of this magnitude will occur. A 100-year flood could occur twice in the same year, two years in a row, or four times in 20 years. A 500-year flood has a 0.2 percent probability of occurrence any given year. Smaller, less extensive and less damaging events happen more frequently, but even 100-year events can occur in back-toback years. Based on the National Weather Service s records of 27 damaging flood events in the time period, or 27 years, a flood occurs somewhere in Dane County on average every year and thus warrants a highly likely occurrence rating. Flooding that merits a presidential disaster declaration (7 events between ) occurs every 5 years on average in the County. Impact Assessment Because of the varied nature and widespread damage floods cause, this profile is not discussed in terms of direct and indirect potential impacts. Instead, each area that flooding impacts is broken down and explained, including an analysis of both direct and indirect Dane County 4.52

53 impacts thereof. The impacts of flooding in Dane County are far ranging. Specific examples of how floods negatively impact Dane County are summarized below: Floods cause damage to private property that often creates financial hardship for individuals and families; Floods cause damage to public infrastructure resulting in increased public expenditures and demand for tax dollars; Floods cause loss of personal income for agricultural producers that experience flood damages; Floods cause loss of income to businesses relying on recreational uses of County waterways; Floods cause emotional distress on individuals and families; Floods can cause injury and death. Health and Safety There is very little available data on health problems caused by flooding in Dane County because data collection mechanisms are varied, particularly in terms of reported occurrences versus actual occurrences. The first impact comes from the water itself and is considered the direct impact of flooding. Floodwaters carry whatever was on the ground that the upstream runoff picked up, including dirt, oil, animal waste, and lawn, farm and industrial chemicals. Pastures and areas where cattle and hogs are kept can contribute polluted waters to the receiving streams. Floodwaters saturate the ground, which can lead to infiltration into sanitary sewer lines. When wastewater treatment plants exceed capacity, there is nowhere for the sewage to flow. Infiltration and lack of treatment lead to overloaded sewer lines that can back up into low lying areas and homes. Even though diluted by floodwaters, raw sewage can be a breeding ground for bacteria, such as E.coli, and other disease causing agents. The second set of health concerns occur after the water is gone, and are considered indirect impacts of flooding. Stagnant pools become breeding grounds for mosquitoes, and wet areas of a building that have not been cleaned breed mold and mildew. A building that is not thoroughly and properly cleaned becomes a health hazard, especially for small children and the elderly. Another health hazard occurs when heating ducts in a forced-air system are not properly cleaned after inundation. When the furnace or air conditioner is turned on, the sediments left in the ducts are circulated throughout the building and breathed by the occupants. Finally, flooding creates long-term psychological impacts on victims. The cost and labor needed to repair a flood-damaged home puts a severe strain on people, especially the unprepared and uninsured. There is also a long-term problem for those who know that their homes can be flooded again. The resulting stress on floodplain residents takes its toll in the form of aggravated physical and mental health problems. This is also considered an indirect impact of flooding. Building Damage In terms of numbers of people affected and total economic losses, damage to buildings, especially residences is usually the County s largest single flood problem. Due to the relatively shallow flood depths, soaking causes the most common type of damage inflicted by a flood. When soaked, many materials change their composition or shape. Wet wood will swell and, if dried too quickly, will crack, split or warp. Plywood can break apart. Gypsum Dane County 4.53

54 drywall will fall apart if it is bumped before it dries out. The longer these materials are wet, the more moisture, sediment and pollutants they will absorb. Walls present a special problem: a wicking effect pulls water up through wood and wallboard, soaking materials several feet above the actual high-water line. Structural damage to buildings has not been a common problem in Dane County. Soaking can also cause extensive damage to household and other building contents. Wooden furniture may become so badly warped that it cannot be used. Other furnishings such as upholstery, carpeting, mattresses, and books usually are not worth drying out and restoring. Electrical appliances and gasoline engines will not work safely until they are professionally dried and cleaned. In short, while a building may look sound and unharmed after a flood, the waters can cause a lot of damage. To properly clean a flooded building, the walls and floors should be stripped, cleaned, and allowed to dry before being recovered. This is expensive and can take weeks. Sewer and Wastewater Sewer and wastewater service and infrastructure are compromised during flooding events in many locations around the County with consequences for homes as shown in Figure Sewer backups in residential basements are the primary result of overtaxed wastewater systems. Survey respondents reported 100 s of residences that have had sewer backup problems. During major storm events, flows to the treatment plants increase, and in some cases triple due to water infiltration into the piping system. Failing pumps, and inflow meter damage, are also a problem. Additionally, flooded roads inhibit the timely repair of pumping stations. Figure 4.10 Number of problemsheds in each watershed impacted by sewer back-ups. Sewer Backups Number of Problemsheds Allen & Middle Sugar Gordon Lower Koshkonong Maunesha Mill and Blue Mounds Upper Sugar River W. Branch Sugar Rive Lake Wisconsin Upper Koshkonong Badfish Roxbury Yahara Kegonsa Black Earth Yahara Mendota Six Mile & Pheasant Yahara Monona Source: 2003 flood mitigation planning survey Commercial Flooding Flooding of commercial structures is not a significant problem in Dane County as shown in Figure Outside the metropolitan area, surveys completed documented only very few Dane County 4.54

55 occurrences of any damage of this type. The majority of commercial flooding occurs on the isthmus between Lake Mendota and Lake Monona, a densely urbanized area, which was historically wetland. Figure 4.11 Number of Impacted Commercial Structures in Each Watershed Commercial Flooding Number of Structures Allen & Middle Sugar Badfish Gordon Lower Koshkonong Maunesha Mill and Blue Mounds Upper Koshkonong Upper Sugar River W. Branch Sugar River Yahara Kegonsa Yahara Mendota Black Earth Roxbury Six Mile & Pheasant Lake Wisconsin Yahara Monona Source: 2003 flood mitigation planning survey. Road, Shoulder, and Ditch Flooding Forty percent of problemsheds reported by survey respondents included flooding on roadways. A possible contributing factor is under-sized culverts that become damaged during high water flows. Very few bridges have been damaged though they may play a role in constricting water flows. This flooding, and often-associated road or ditch damage, inhibits emergency vehicle movement and could compromise public safety. Dane County 4.55

56 Figure 4.12 Number of problemsheds in each watershed that have been impacted by road, ditch or culvert damage Road/Culvert Flooding Number of Problemsheds Upper Sugar River Lower Koshkonong W. Branch Sugar River Gordon Lake Wisconsin Maunesha Roxbury Allen & Middle Sugar Yahara Kegonsa Badfish Mill and Blue Mounds Yahara Mendota Black Earth Upper Koshkonong Six Mile & Pheasant Yahara Monona Source: 2003 flood mitigation planning survey Farmland Flooding Dane County is the one of the most fertile counties in the state of Wisconsin, and as a result farming plays a major role in the local economy. Flooding of farm fields and crop loss is an additional stress on an already highly stressed profession. The amount of crop loss in the County per acre varies across the landscape depending upon the topography generally the more flat the land the more pervasive the problem. The east side of the County experiences relatively severe crop losses on occasion; the west side of the County, though not without this impact, is less affected. Crop loss is capricious timing of storms, duration of standing water, and type of crops play a part. Prolonged flooding occurring while crops are immature can lead to total crop loss for a year. Corn, for instance, has difficulty withstanding flooded soil. Flooding of short duration or later in the growing season may have little or no effect on the harvest. Floods have caused crop losses throughout the County. Figure 4.13 shows that the most heavily affected area is the Upper Koshkonong watershed. Total acres affected by flooding reported through the 2003 survey approaches 5,500 acres and losses are in the 10 s of millions of dollars over The owners of approximately 55 different parcels of land have filed for flood insurance claims countywide. Dane County 4.56

57 Figure 4.13 Number of Acres of Agricultural Land in Each Watershed that Have Been Impacted by Severe Flooding Farmland Flooding Number of Acres Badfish Gordon Lake Wisconsin Six Mile & Pheasant W. Branch Sugar River Yahara Kegonsa Yahara Monona Mill and Blue Mounds Allen & Middle Sugar Black Earth Yahara Mendota Upper Sugar River Roxbury Maunesha Lower Koshkonong Upper Koshkonong Source: 2003 flood mitigation planning survey. Erosion and Stream Pollution Due to the agricultural character of rural Dane County, erosion is a concern. Ditches that once conveyed water quickly have become laden with soil, decreasing their capacity to convey water. Construction sites also contribute to siltation in streams. Siltation and trash also compromise stream quality. Ongoing and successful stream restoration projects, and the depositing of organic materials in streams, increase woody matter in stream channels. The buildup of organic material slows water flows. Woody material builds up along the buttresses of bridges and other human-made obstructions in the river channels and alongside river channels themselves. While the slowing of water may be beneficial for downstream residents, areas where the build-ups occur increase the risk of flooding. Impact Magnitude and Severity Summary Due to the wide variety and severity of the impacts that flooding can have in Dane County an overall critical impact magnitude and severity rating is appropriate. Dane County 4.57

58 Vulnerability Assessment Population Vulnerable populations in Dane County include residents living in known flooding areas or near areas vulnerable to flash floods. Special population include the students at the University of Wisconsin at Madison, those living in long-term care facilities, mobile homes, hospitals, and temporary shelters, people who speak English poorly, tourists and visitors, the elderly and very young, and those with developmental, physical or sensory disabilities. These populations may be more vulnerable to flooding because of limitations on movement, fiscal income, challenges in receiving and understanding warnings, or unfamiliarity with surroundings. As part of this plan s 2009 update an estimate of the population exposed to flooding was created using a GIS overlay of the 2008 DFIRM on potentially flooded residential parcels. The total number of residential parcels was aggregated by municipality and multiplied by the average household size in Dane County (2.43 persons) to estimate population resident in the 100 year and 500 year flood zones. According to this analysis, 2,474 persons are potentially vulnerable to flooding from the 100-year event, and an additional 936 are vulnerable to the 500-year event. The City of Madison, Village of DeForest, City of Stoughton and Town of Dunn all have more that 200 persons resident in the floodplain. the City of Monona, the villages of Cross Plains and Mazomanie and towns of Westport, Pleasant Springs, Albion and Mazomanie have between persons in the 100 year floodplain. The HAZUS-MH analysis performed for the State Mitigation Plan update in 2008 estimates that 4,340 households would be displaced by 100-year floods, and that 8,107 would seek temporary shelter in public shelter. The HAZUS methodology is more general and likely overestimates the population vulnerability. Table 4.12 Floodprone Population Estimate Jurisdiction Population Est. 100-yr Flood Zone Population Est. Flood Zone X500 Total Population Estimate City of Madison City of Middleton City of Monona City of Stoughton City of Sun Prairie City of Verona Village of Belleville Village of Black Earth Village of Cambridge Village of Cottage Grove 2-2 Village of Cross Plains Village of DeForest Village of Marshall Village of Mazomanie Village of McFarland Village of Oregon Dane County 4.58

59 Jurisdiction Population Est. 100-yr Flood Zone Population Est. Flood Zone X500 Total Population Estimate Village of Rockdale Village of Waunakee Town of Albion Town of Berry 5-5 Town of Black Earth 7-7 Town of Blue Mounds 2-2 Town of Bristol Town of Burke Town of Christiana Town of Cottage Grove Town of Cross Plains Town of Deerfield 2-2 Town of Dunkirk 7-7 Town of Dunn Town of Madison Town of Mazomanie Town of Medina 5-5 Town of Montrose Town of Oregon 7-7 Town of Perry 2-2 Town of Pleasant Springs Town of Roxbury Town of Rutland 7-7 Town of Springdale 2-2 Town of Springfield 5-5 Town of Sun Prairie 7-7 Town of Vermont 5-5 Town of Verona 7-7 Town of Westport Town of Windsor Total 2, ,409 Historical data yields little information on deaths or injuries by flooding and flash flooding in the County. This is likely due to the slow-rise nature of flooding around lakes and lowlands, giving people adequate time to evacuate. Most flood deaths and injuries are associated with persons who try to drive vehicles into flooded roads and underestimate the depth and velocity of floodwaters. General Property Flooding of residential structures in Dane County is a major concern. This type of flooding has several causes: river flooding, high lake levels, sewer backups, stormwater runoff from Dane County 4.59

60 urban areas as well as farmland, and high groundwater. Effects include flooded basements and first floor flooding. Combinations of these elements have damaged many structures and put even greater numbers at risk. Table 4.12 demonstrates the number of residents impacted by flooding from the major watersheds and rivers in the Dane County area. Figure 4.15 illustrates the levels of flooded basements for each watershed, and Figure 4.14 displays the number of residences flooded into the first floor. Figure 4.14 Number of Problemsheds in Each Watershed that Have Been Impacted by First Floor Flooding First Floor Flooding 6 Number of Problemsheds Allen & Middle Sugar Gordon Lake Wisconsin Lower Koshkonong Maunesha Mill and Blue Mounds Upper Koshkonong Upper Sugar River W. Branch Sugar River Badfish Black Earth Roxbury Yahara Kengonsa Yahara Mendota Six Mile & Pheasant Yahara Monona Source: 2003 flood mitigation planning survey. Dane County 4.60

61 Figure 4.15 Number of Problemsheds in Each Watershed that Have Been Impacted by Flooded Basements. Basement Flooding Number of Problemsheds Gordon Lower Koshkonong Mill and Blue Mounds W. Branch Sugar River Allen & Middle Sugar Maunesha Upper Sugar River Lake Wisconsin Badfish Upper Koshkonong Roxbury Yahara Kengonsa Six Mile & Pheasant Yahara Mendota Black Earth Yahara Monona Source: 2003 flood mitigation planning survey. Repetitive Loss Properties A repetitive loss property is one that has received two or more flood insurance claim payments for at least $1,000 each in any 10 year period since There are thirteen repetitive loss properties in Dane County, which is an increase from the seven identified in The general locations of these properties are illustrated in Figure These properties are important to the National Flood Insurance Program because they account for one-third of national flood insurance claim payments. There are several FEMA programs that encourage communities to identify the causes of their repetitive losses and develop a plan to mitigate the losses. The repetitive loss properties in the County are all residential structures and are scattered around the County, thus there are not many distinct repetitive loss areas. There are two located in the City of Monona and three in the Village of Oregon. The Village of Mazomanie, Village of Black Earth, Village of DeForest, City of Madison, Town of Madison, Town of Roxbury, Town of Albion, and Town of Cottage Grove have one each. Addressing the areas where these repetitive losses occur is both a County and national priority. Dane County 4.61

62 Figure 4.16 Dane County Repetitive Flood Loss Properties Dane County 4.62

63 Essential Infrastructure, Facilities, and Other Important Community Assets GIS analysis of flood hazards and recently developed critical facilities databases during the 2009 update of this plan indicate that there are several critical facilities that are potentially exposed to the flood hazard. A summary table of the potentially impacted facilities can be referenced in Section 4.3 Vulnerability Summary. A map of the location of critical facilities within the floodplain is shown in Figure Detailed facility information can be referenced in the jurisdictional annexes. 259 structures were identified as within the DFIRM 100-year flood zone. 173 of those structures are manufactured homes, leaving 86 facilities of other types. 36 of the other types are bridges, which may or may not be susceptible to flood damage or inundation. 42 structures were identified as within the DFIRM 500-year flood zone, 19 of which are manufactured homes. An additional 100 structures were identified in flood hazard areas delineated by FEMA s HAZUS-MH program that are not in a DFIRM flood zone. Dane County 4.63

64 Figure 4.17 Critical Facilities Potentially Vulnerable to Flooding Dane County 4.64

65 Natural, Historic and Cultural Resources Natural resources are generally resistant to flooding except where natural landscapes and soil compositions have been altered for human development or after periods of previous disasters such as drought and fire. Wetlands, for example, exist because of natural flooding incidents. Areas that are no longer wetlands may suffer from oversaturation of water, as will areas that are particularly impacted by drought. Areas recently suffering from wildfire damage may erode because of flooding, which can permanently alter an ecological system. Vulnerable cultural resources include the University of Wisconsin campus located in downtown Madison. GIS analysis of flood hazards and historic structure databases during the 2009 update of this plan indicate that there are eight historic properties that are potentially vulnerable to flooding (5 in the 100-yr, 2 in the 500-yr, and 1 in a HAZUS only flood area). No further detail on the historic structures was available. Estimating Potential Losses and Development Trends Assessment Potential Loss Estimates Given the interplay of the contributing influences, the potential exists for flood damages to continue to rise. While the potential for future damages is difficult to calculate accurately, there are indicators and acceptable methods for estimating future losses. Residential Losses The Federal Emergency Management Agency recommends a methodology of estimating future losses based on an inventory of buildings and structures that lie within the flood hazard boundary of the 100-year flood event. Table 4.13 provides an estimate of the extent of damage from various flood depths on different types of structures. This table is from FEMA s cost-benefit analysis module and has been compiled based on flood damage data from across the country. To utilize this table, the approximate elevations of both the building first floor and the water level during the 100-year flood are needed. From the 100- year flood elevation, subtract the first floor elevation of the building. This figure then can be used to estimate the extent of damage to the type of building that was flooded. For example, if the 100-year flood event elevation is approximately 848 feet above mean sea level and a one story home assessed at $112,000 has a first floor elevation of 844 feet, it is estimated that this four feet of flooding would cause 28 percent or $31,360 in damage to the building. Table 4.13 Estimation of Damage to Structures First Floor Flood Depth (Feet) One Story No Basement (% of Building Damaged) Two Story No Basement (% of Building Damaged) One or Two Story with Basement (% of Building Damaged) Manufactured Home (% of Building Damaged) Dane County 4.65

66 First Floor Flood Depth (Feet) One Story No Basement (% of Building Damaged) Two Story No Basement (% of Building Damaged) One or Two Story with Basement (% of Building Damaged) Manufactured Home (% of Building Damaged) > Source: Federal Emergency Management Agency. Estimation of damage potential to buildings based on flood depth relative to the first floor of the building. The negative numbers in the First Floor Flood Depth column indicate flood levels that are lower than the first floor of the building. The resulting flood damage potential is expressed as a percentage of the assessed value of the building. Flooding also causes damages to the contents of buildings that are flooded. Table 4.14 provides a method for estimating the damage potential to building contents. Contents damage includes damage to furniture, appliances, clothing, and other incidental items not included in the building value. Table 4.14 Estimation of Damage to Building Contents First Floor Flood Depth (Feet) One Story No Basement (% of Building Damaged) Two Story No Basement (% of Building Damaged) One or Two Story with Basement (% of Building Damaged) Manufactured Home (% of Building Damaged) > Source: Federal Emergency Management Agency. Estimation of damage potential to building contents based on flood depth relative to the first floor of the building. The negative numbers in the First Floor Flood Depth column indicate flood levels that are lower than the first floor of the building. The resulting flood damage potential is expressed as a percentage of the total value of the building contents. During the 2003 development of the Flood Mitigation Plan a detailed flood loss assessment for Dane County was estimated by using a comparison of a digital version of FEMA s Flood Insurance Rate Maps, Dane County parcel data, and the single and two family residence inventory conducted in 2000 by the Capital Area Regional Planning Commission. While it took a detailed approach, including a method of estimating first finished flood elevations based on GIS-based 2-ft contours, it was limited to the available data at the time and did Dane County 4.66

67 not estimate losses for several structures located in A zones. assessment were summarized by watershed. The results of that During the 2009 update improvements to flood hazard data and inventory data were used to develop a comprehensive flood risk assessment. This included an analysis of all property types that are potentially within mapped floodplains, aggregated by jurisdiction. The County s 2008 DFIRM was used as the primary flood hazard layer. In addition to the DFIRM, a flood hazard polygon and depth grid was available that was produced during a countywide flood risk analysis using FEMA s HAZUS-MH. This was developed during the update to the Wisconsin State Hazard Mitigation Plan. Though the flood hazard areas delineated by this program may not be as accurate as the DFIRM, in most areas they are consistent. The advantage to the HAZUS-MH depth grid is that the depth of flooding can be visualized and analyzed, communicating how the risk varies with flood depth. The flood depth was analyzed by jurisdiction, represented in Table The average flood depth for the county is 2.5 ft. To create a comprehensive flood hazard layer, the DFIRM and HAZUS-MH flood polygon layers were merged. The County parcel layer, with 2008 assessed valuations data linked to it, was used as the inventory basis. This was used instead of a structure footprint layer, which was not complete in some urban areas of the County. This layer was intersected with land use and municipal boundary GIS layers so those attributes could be used for aggregation and analysis purposes. Using GIS analysis, parcels that intersected the flood hazard layer and that had an improved value greater than zero were selected. This parcel layer was converted to centroids or points that represent the center of a parcel. Those parcels whose center was not within a flood hazard zone were removed from the analysis. Those with their center within the flood hazard layer were assumed to be potentially flood prone. The improved value was assumed to be the structure value, and the contents value was estimated at 50 percent of the improved value. Using the 2 ft flood as the average depth and assuming a one or two story building with basement, a depth-damage ratio of 20 percent was applied to the exposed structure and estimated content value to develop the loss estimate. While there are limitations to this assessment, and in certain ways it is not as detailed as the 2003 assessment, it does provide a consistent method to estimate loss. The overall loss estimate to the County is shown in Table 4.15 by general land use. Over 1,600 improved parcels are potentially at risk, the majority of them residential. Flood loss totals could exceed $105 million. Note that this analysis does not account for property that may have been elevated to or above the 100-year floodplain, thus it assumes no mitigation in place. This analysis does not capture flood losses in areas outside of mapped floodplains, which is known to be a problem in the County, thus it may actually underestimate the potential losses. According to the HAZUS- MH flood loss done for the State Hazard Mitigation Plan, total losses from flooding are estimated at $460 million. HAZUS-MH inventory data is more generalized that the analysis presented below, but it also accounts for relocation costs, lost wages, and rental income losses, which are not accounted for in this analysis. Table 4.15 County Flood Loss Estimate Summary DFIRM 100 Year Flood Property Type Improved Parcel Count Improved Values Contents Value Total Values (Content & Imp.) Estimated Loss Residential 1,018 $184,289,200 $92,144,600 $276,433,800 $55,286,760 Other 361 $80,220,600 $40,110,300 $120,330,900 $24,066,180 Dane County 4.67

68 Property Type Improved Parcel Count Improved Values Contents Value Total Values (Content & Imp.) Estimated Loss Agriculture 192 $28,228,300 $14,114,150 $42,342,450 $8,468,490 Commercial Services 31 $24,640,200 $12,320,100 $36,960,300 $7,392,060 Industrial 15 $15,104,900 $7,552,450 $22,657,350 $4,531,470 Commercial Sales 20 $14,237,200 $7,118,600 $21,355,800 $4,271,160 Transportation 5 $3,283,200 $1,641,600 $4,924,800 $984,960 Institutional/Government 3 $1,483,300 $741,650 $2,224,950 $444,990 Total 1,645 $351,486,900 $175,743,450 $527,230,350 $105,446,070 In addition to the 100-year event, the additional damage from a 500-year flood was analyzed. Table 4.16 shows the summary of property types that are located within a 500- year flood zone, according to the 2008 DFIRM. The table indicates an additional $252 million in property is exposed to this hazard and could result in another $50 million in losses. Table 4.16 County Flood Loss Estimate Summary DFIRM 500 Year Flood Property Type Improved Parcel Count Improved Values Contents Value Total Values (Content & Imp.) Estimated Loss Residential 385 $51,731,600 $25,865,800 $77,597,400 $15,519,480 Other 43 $26,119,300 $13,059,650 $39,178,950 $7,835,790 Commercial Sales 35 $15,426,300 $7,713,150 $23,139,450 $4,627,890 Commercial Services 29 $43,651,800 $21,825,900 $65,477,700 $13,095,540 Industrial 26 $25,426,300 $12,713,150 $38,139,450 $7,627,890 Recreation 23 $5,743,900 $2,871,950 $8,615,850 $1,723,170 Total 541 $168,099,200 $84,049,600 $252,148,800 $50,429,760 The 2008 DFIRM data also allowed an analysis of properties located in the floodway, or zone of 100-year flooding that is anticipated to have the greatest depths and velocities. Table 4.17 is a summary of these properties, which could be considered a priority for mitigation. According to this analysis Deforest, Cross Plains, Verona, Cottage Grove, Black Earth, Mazomanie have the highest concentrations of properties in the floodway. Table 4.17 County Summary of Floodway Properties Property Type Improved Parcel Count Improved Values Contents Value Total Values (Content & Imp.) Estimated Loss Residential 152 $22,903,600 $11,451,800 $34,355,400 $6,871,080 Other 67 $14,517,900 $7,258,950 $21,776,850 $4,355,370 Agriculture 26 $4,390,000 $2,195,000 $6,585,000 $1,317,000 Commercial Sales 5 $3,598,400 $1,799,200 $5,397,600 $1,079,520 Dane County 4.68

69 Property Type Improved Parcel Count Improved Values Contents Value Total Values (Content & Imp.) Estimated Loss Commercial Services 4 $2,852,600 $1,426,300 $4,278,900 $855,780 Industrial 4 $860,400 $430,200 $1,290,600 $258,120 Total 258 $49,122,900 $24,561,450 $73,684,350 $14,736,870 A summary of the loss by jurisdiction is provided in Table 4.18, sorted by number of improved parcels in the floodplain. Note that the highest count of floodprone parcels does not necessarily indicated the highest flood losses, since the loss is dependent on the value of the exposed property. According to this analysis the Town of Dunn, City of Madison, City of Stoughton and Village of Deforest have more than 100 developed properties within the floodplain. The City of Middleton, City of Madison, City of Stoughton and City of Monona have the potential for the highest dollar losses. A countywide map with the locations of these developed, potentially flood-prone parcels, is shown in Figure More detailed maps and tables are included in the jurisdictional annexes. Table Year Flood Loss Summary by Jurisdiction Jurisdiction City of Fitchburg Total City of Madison Total City of Middleton Total Avg Depth of flood (ft) Improved Parcel Count Improved Values Content Total Values (Content & Imp.) Estimated Loss $825,000 $412,500 $1,237,500 $247, $31,155,300 $15,577,650 $46,732,950 $9,346, $44,842,600 $22,421,300 $67,263,900 $13,452,780 City of Monona Total $26,874,700 $13,437,350 $40,312,050 $8,062,410 City of Stoughton Total City of Sun Prairie Total $28,948,800 $14,474,400 $43,423,200 $8,684, $1,775,100 $887,550 $2,662,650 $532,530 City of Verona Total $5,633,900 $2,816,950 $8,450,850 $1,690,170 Village of Belleville Total Village of Black Earth Total Village of Cambridge Total Village of Cottage Grove Total Village of Cross Plains Total Village of DeForest Total Village of Marshall Total $384,000 $192,000 $576,000 $115, $5,304,200 $2,652,100 $7,956,300 $1,591, $2,440,300 $1,220,150 $3,660,450 $732, $163,800 $81,900 $245,700 $49, $7,395,300 $3,697,650 $11,092,950 $2,218, $21,229,100 $10,614,550 $31,843,650 $6,368, $4,549,500 $2,274,750 $6,824,250 $1,364,850 Dane County 4.69

70 Jurisdiction Village of Mazomanie Total Village of McFarland Total Village of Oregon Total Village of Rockdale Total Village of Waunakee Total Avg Depth of flood (ft) Improved Parcel Count Improved Values Content Total Values (Content & Imp.) Estimated Loss $6,733,200 $3,366,600 $10,099,800 $2,019, $4,144,000 $2,072,000 $6,216,000 $1,243, $4,954,300 $2,477,150 $7,431,450 $1,486, $489,100 $244,550 $733,650 $146, $8,886,600 $4,443,300 $13,329,900 $2,665,980 Town of Albion Total $6,525,700 $3,262,850 $9,788,550 $1,957,710 Town of Berry Total $1,425,700 $712,850 $2,138,550 $427,710 Town of Black Earth Total Town of Blooming Grove Total Town of Blue Mounds Total $1,848,400 $924,200 $2,772,600 $554, $597,200 $298,600 $895,800 $179, $1,462,200 $731,100 $2,193,300 $438,660 Town of Bristol Total $4,082,900 $2,041,450 $6,124,350 $1,224,870 Town of Burke Total $4,624,700 $2,312,350 $6,937,050 $1,387,410 Town of Christiana Total Town of Cottage Grove Total Town of Cross Plains Total Town of Deerfield Total Town of Dunkirk Total $2,082,900 $1,041,450 $3,124,350 $624, $6,507,700 $3,253,850 $9,761,550 $1,952, $1,681,200 $840,600 $2,521,800 $504, $1,649,600 $824,800 $2,474,400 $494, $3,109,100 $1,554,550 $4,663,650 $932,730 Town of Dunn Total $16,637,400 $8,318,700 $24,956,100 $4,991,220 Town of Mazomanie Total Town of Medina Total Town of Middleton Total Town of Montrose Total Town of Oregon Total $7,509,500 $3,754,750 $11,264,250 $2,252, $4,082,500 $2,041,250 $6,123,750 $1,224, $235,200 $117,600 $352,800 $70, $5,243,300 $2,621,650 $7,864,950 $1,572, $3,184,000 $1,592,000 $4,776,000 $955,200 Town of Perry Total $550,600 $275,300 $825,900 $165,180 Town of Pleasant Springs Total Town of Primrose Total $12,780,100 $6,390,050 $19,170,150 $3,834, $541,500 $270,750 $812,250 $162,450 Dane County 4.70

71 Jurisdiction Town of Roxbury Total Town of Rutland Total Town of Springdale Total Town of Springfield Total Town of Sun Prairie Total Town of Vermont Total Town of Verona Total Town of Vienna Total Town of Westport Total Town of Windsor Total Avg Depth of flood (ft) Improved Parcel Count Improved Values Content Total Values (Content & Imp.) Estimated Loss $5,132,900 $2,566,450 $7,699,350 $1,539, $3,003,800 $1,501,900 $4,505,700 $901, $5,328,100 $2,664,050 $7,992,150 $1,598, $1,820,800 $910,400 $2,731,200 $546, $3,886,600 $1,943,300 $5,829,900 $1,165, $3,955,200 $1,977,600 $5,932,800 $1,186, $4,340,100 $2,170,050 $6,510,150 $1,302, $7,000 $3,500 $10,500 $2, $22,003,900 $11,001,950 $33,005,850 $6,601, $7,156,100 $3,578,050 $10,734,150 $2,146,830 Town of York Total $1,762,200 $881,100 $2,643,300 $528,660 Grand Total 1,645 $351,486,900 $175,743,450 $527,230,350 $105,446, Flood Damage Analysis Dane County Emergency Management requested FEMA Individual Assistance claims data associated with the 2008 flood disaster to supplement the analysis of the flood hazard for this plan. The County geo-located the addresses of those that requested and received Individual Assistance from FEMA, indicating that they were impacted by flooding. 1,627 total claims were able to be geolocated with GIS. This enabled them to be analyzed in relation to other flood hazard layers in GIS, including the DFIRM, HAZUS, and hydric soils layers. In general the claims were in scattered locations around the County. The exceptions were clusters in the Villages of Deforest, Marshall and Sun Prairie and the City of Monona. There is also a significant cluster of claims in the Town of Cottage Grove. Privacy restrictions with the data prevented it from being published in the plan. Interestingly, the majority did not intersect either of the mapped flood hazard areas. The breakdown resulted in the following: DFIRM 100 year zone: 34 claims DFIRM 500 year zone: 46 claims HAZUS (where not coincident with DFIRM): 57 claims Hydric soils: 158 claims None of the above: 1,445 claims This preliminary analysis leads to some initial conclusions: Much of the flood risk is outside of mapped floodplains. Dane County 4.71

72 Stormwater drainage issues may be more of an issue than floodplain-related flooding High groundwater table flooding may be more of an issue than floodplain-related flooding Hydric soils areas do contribute to flood problems, but perhaps not as much as initially believed. Mitigation and floodplain management is working in Dane County mapped floodplains. Properties identified in the floodplain with the parcel-dfirm modeling do not account for elevation or floodproofing that may be in place. A more detailed analysis of the flood risk in Dane County is needed to refine the flood problems and solutions, or quantify the losses avoided from floodplain management activities. Development Trends Dane County s continued population, housing, and employment growth, creates pressure for land use change and the supporting infrastructure improvements. Floodplain management practices implemented through local floodplain management ordinances should mitigate the flood risk to new development in floodplains. The County s Floodplain development permits are tracked using a paper log that eventually is transferred into a database. This system did not allow an analysis of floodplain development trends during the 2009 update to this plan, as many permits remained to be entered into an electronic log. Urbanization and increasing impervious surface areas tend to increase both the rate and the volume of stormwater runoff. Problems with the regional volume of stormwater runoff remain. Particularly in the case of the Yahara Lakes, it appears that the lakes are acting as a large wet detention basin, holding ever-increasing volumes of stormwater runoff. Thus the largest issue with development trends is urbanization and stormwater drainage issues that add to the volume of floodwaters in floodplains. Overall Risk Summary Overall, flooding presents a high risk for Dane County. The events occur frequently and have caused damage over significant portions of the county. Although flooding affects residents countywide, based on analysis of past flood events, survey data, and future damage potential estimates, the following areas of the County emerge as areas where there is a likelihood of continued problems in the future. Dane County 4.72

73 Figure 4.18 Flood Risk Map Dane County 4.73

74 Residential flooding and corresponding losses in the entire Yahara River Basin has been a significant problem in the past. The damage potential for a 100-year flood indicates that the highest monetary loses in the County would be experienced along the Yahara River and Chain of Lakes. Details of the losses estimated for each jurisdiction indicate that the City of Madison, City of Monona, City of Middleton, and Village of De Forest could continue to experience damaging flood events. Residential flooding and corresponding losses in the Black Earth Creek Watershed has also been a significant problem in the past. The damage potential analysis indicates that Black Earth Creek Watershed has more buildings located within the mapped floodplain than any other watershed in the County. While the potential monetary losses are not as high as those in the Yahara River Basin, a 100-year flood in the Black Earth Creek Watershed is likely to impact a greater number of people than a similar event in any other individual watershed. These most at-risk communities, including Mazomanie Village and Town, and Black Earth Village and Town, chose not to participate in this plan during the 2009 update. Agricultural flooding and corresponding crop loss in the Upper Koshkonong Creek Watershed. Residential flooding in the Roxbury Creek Watershed. Areas at risk of future flood losses include the hamlet of Roxbury, Fish Lake, and the floodplain of the Wisconsin River. Residential flooding from high groundwater tables in areas of hydric soils and poor drainage. Table 4.19 provides the summary of how all aspects of the hazard profile were evaluated to establish an overall hazard rating. Table 4.19 Overall Risk Summary for Flooding Measurement Rating Value Geographic Extent Significant 3 Probability of Future Occurrence Highly Likely 4 Vulnerability High 3 Magnitude/Severity Critical 3 Overall Risk Rating: High Fog Description Fog is a cloud made up of water droplets suspended in the air at the earth's surface. Fog forms when air is cooled to its dew point, which is the temperature at which air is saturated with moisture. When air reaches its dew point it condenses into very small particles, forming the tiny water droplets that create clouds. When this occurs very close to the ground, the event is called fog. The intensity and duration of fog varies with the location and type of fog. Severity ranges from early morning ground fog that burns off easily to prolonged valley fog that can last for days. Generally, strong winds prevent fog formation. The following list summarizes several possibilities for the formation, intensity, and duration of fog in the upper Midwest, as compiled in the Hazardous Weather Resource Guide by FEMA: Dane County 4.74

75 Ground Fog is associated with clear nights, stable air (winds less than 5 mph), and a smalltemperature dew point range. It forms when heat radiates away from the ground, cooling the ground and surface air. When air cools to its dew point, fog forms, usually a layer of less than feet. It is common in many areas of the United States and generally burns off from the morning sun. Advection Fog is associated with horizontal wind, warm, humid air, and winter temperatures. It forms when wind pushes warm humid air over the cold ground or water, where it cools to the dew point and forms fog. Advection fog can cover wide areas of the central U.S. in winter. During the winter this is common when snow covers much of the Midwest. The snow cools the bottom portion of the moist air mass often resulting in condensation. This type of fog can be widespread, covering very large areas. Evaporation Fog is associated with bodies of water. It forms as cold air blows over warmer water, causing the water to evaporate into the cold air, increasing the humidity to the dew point. Vapor condenses, forming a layer of fog 1 to 2 feet thick over the water. It can form over ponds and streams on fall days. Precipitation Fog is associated with warmer rain and cooler air. It forms when rain evaporates, and the added vapor increases the air to its dew point. The vapor then condenses into fog. Precipitation fog forms on cool, rainy days. Geographic Extent Fog may occur anywhere in the county, at any point during the day. Records indicate fog is most likely in the early morning or late evening. Dense fog occurs during every month of the year in Wisconsin. It is more common during the cooler months of September through April. During the fall and spring, fog is more common during the early morning hours and during the winter fog can occur anytime favorable conditions are present. Fog is a semiregional phenomenon, affecting large portions of the county simultaneously. It may also form in patches, or uniformly across the entire region or county. Based on the available data, fog incidents are expected to cover between 50 and 100 percent of the county, resulting in an extensive geographic extent rating. Previous Occurrences The National Weather Service (NWS) and the National Climatic Data Center (NCDC) have been tracking fog and dense fog occurrences since This information is captured in Table Some selected descriptions are compiled below. The majority of these descriptions are also drawn from the NCDC database. Additional sources are cited appropriately. Table 4.20 Fog/Dense Fog Events in Dane County ( ) Date Time Type Date Time Type 12/03/ :00 AM Fog 02/20/ :00 AM Fog 12/12/ :00 PM Fog 04/13/ :00 AM Fog 01/09/ :00 AM Fog 03/20/ :00 AM Dense Fog 02/25/ :00 AM Fog 03/23/ :00 AM Dense Fog 03/20/ :00 PM Fog 2/26/ :00 AM Dense Fog Dane County 4.75

76 Date Time Type Date Time Type 08/23/ :00 AM Fog 10/12/ :00 AM Dense Fog 08/24/ :00 AM Fog 10/28/ :00 PM Dense Fog 10/23/ :00 PM Fog 12/9/ :00 PM Dense Fog 10/25/ :00 AM Fog 12/27/ :00 PM Dense Fog 01/12/ :00 AM Fog 03/06/ :00 AM Dense Fog 01/14/ :00 PM Fog 03/09/ :00 AM Dense Fog 02/24/ :30 PM Fog 03/29/ :00 AM Dense Fog 03/22/ :00 AM Fog 05/09/ :00 PM Dense Fog 04/07/ :00 AM Fog 09/14/ :00 AM Dense Fog 05/25/ :00 AM Fog 09/23/ :00 AM Dense Fog 06/07/ :30 PM Fog 03/09/ :00 PM Dense Fog 08/22/ :00 PM Fog 03/25/ :00 AM Dense Fog 09/30/ :00 AM Fog 11/20/ :00 AM Dense Fog 11/15/ :30 PM Fog 12/19/ :00 AM Dense Fog 12/02/ :30 AM Fog 01/07/ :00 AM Dense Fog 12/16/ :15 PM Fog 02/04/ :00 AM Dense Fog Source: The National Climactic Data Center. Available online at last accessed on February 4, January 9, 2000 Dense fog with visibilities frequently near or below 1/4 mile blanketed south-central and southeast Wisconsin for about 29 hours, leading to many airline delays or cancellations at area airports. Area newspapers noted dozens of vehicle accidents. South to southeast winds pulled mild air (maximum temperatures in the upper 30s to lower 40s) into southern Wisconsin resulting in considerable snowmelt, while scattered light rain passed overhead. Consequently, there were ample amounts of low-level moisture to initiate the widespread dense fog. November 15, 2001 Dense fog developed overnight across parts of south-central and southeast Wisconsin, lowering visibilities to near zero to 1/4 mile. The lowest visibilities were found in river valleys west of a line from Madison (Dane Co.) to Beloit (Rock Co). Local airplane traffic was delayed until visibilities improved. Several vehicle accidents were noted in newspapers. In northwest Dane County near Mazomanie on Highway 78, the driver of a vehicle was killed when the vehicle struck a horse standing on the road (fatality indirectly related to fog). Visibility was reported to be about 10 feet around the accident time of about 1:45 a.m. on November 16th. Sixteen children were injured (indirectly related to fog) when a truck struck a Monticello (Green Co.) school bus at 7:46 am on the 16th. Poor visibility was an indirect factor in this accident. The dense fog resulted from the combination of clear skies and light winds after a couple days of rain. Dane County 4.76

77 February 20, 2002 Dense fog developed overnight across south central and southeast Wisconsin due to light rain and persistent, on-shore southeast to northeast winds. Visibility was reduced to 1/8 to 1/4 mile, especially in river valleys and other low spots. This led to several vehicle accidents and flight delays or cancellations at airports. March 20, 2003 Dense fog developed early on March 20th, and dropped visibilities to 1/4 mile or less. Air traffic was delayed or grounded at both Milwaukee's Mitchell Field (Milwaukee Co.), and Dane County Regional Airport. Several school districts delayed school openings by 2 hours, and newspapers reported many vehicle accidents. The dense fog was the result of clear skies, a light south-southeast surface wind, and leftover, low-level moisture February 26, 2004 Dense fog developed overnight, resulting in visibilities of 1/4 mile or less. Newspaper reports indicated that many icy frost deposits occurred on roads and bridges. Snowmelt due to maximum temperatures in the mid to upper 30s on February 25th contributed the moisture needed to saturate the air as the night progressed. Newspaper reports indicated that some airplane flights were delayed and at least a dozen vehicle accidents occurred. October 12, 2004 Dense fog developed overnight, reducing visibilities to 1/8 to 1/4 miles. Some school buses were delayed a couple hours, and some airplane traffic was delayed. December 28, 2005 Dense fog developed overnight over much of south-central and southeast Wisconsin, resulting in the delay or cancellation of some airline flights from Milwaukee Mitchell Field (Milwaukee County). Visibilities fell to 1/8 to 1/4 mile. The dense fog was a result of light southeast winds, a moist low-level atmosphere, and snow-melt. September 14, 2006 Dense fog developed overnight across parts of south-central and southeast Wisconsin, thanks to clear skies, light winds, and a very moist ground due to recent rains. Visibilities were reduced to zero to 1/4 mile. One person was killed (indirectly-related death) in a vehicle accident southwest of Whitewater and just inside Walworth County. There was another driver killed (indirectly-related death) in a vehicle accident near Madison (Dane Co.). Several airplane flights were delayed or cancelled at Madison's Truax Field and other local airports. November 20, 2007 A moist, low-level flow ahead of a Dakota low pressure allowed dense fog to develop over Sauk, Washington and Dane Counties. Dew points started off in the 40s but dropped into the 30s as the low pressure moved east along the Wisconsin-Illinois border to southern Lake Michigan. Visibilities dropped to 1/8 to 1/4 mile. Some airplane flights were delayed or cancelled. The media noted a few vehicle accidents. Over the remainder of south-central and southeast Wisconsin visibilities dropped only to 1/2 to 1 mile. Dane County 4.77

78 December 19, 2007 Dense freezing fog developed over parts of south-central and southeast Wisconsin and reduced visibilities to 1/8 to 1/4 mile. Untreated road and sidewalk surfaces were coated with thick rime/frost, as well as trees and other cold-surface objects. Newspaper reported indicated that at least a dozen vehicle accidents occurred in each county listed in this event. Moist air moving over a cold, snow-covered terrain initiated the dense freezing fog. Several airline flights were delayed or canceled at Madison Truax Field. January 6, Dense fog caused a 100 car pile-up traffic accident which stretched about 5 miles long along Interstate 39/90. There were many injuries, with approximately 54 individuals taken to area hospitals. Two indirect deaths were reported. February 4, 2008 Widespread dense fog developed after sunset across a good portion of south-central and southeast Wisconsin. Visibilities were reduced to 1/8 to 1/4 mile. The area affected was mostly southeast of a line from Darlington to Madison to Beaver Dam to Sheboygan. Several flights were canceled or delayed at Milwaukee Mitchell Field and other airports. The media noted a few vehicle accidents. Synoptically, diminishing winds, night-time cooling, and a very moist air mass near the ground allowed the dense fog to develop. Probability of Future Occurrences The frequencies of past dense fog events provide a base line to predict the risk of future occurrences. Fog events are documented multiple times each year, and there are no climactic indications that these occurrences will change in the measurable future. Based on the past history of events, dense fog has a 100 percent chance of occurrence in a given year, which correlates to a highly likely occurrence rating. Impact Assessment Direct Impacts Direct impacts are rated based on the actual affect of fog on the category being evaluated. The most common direct impact of fog is reduced visibility for motorists. Fog ranges in intensity, duration, and density, with a highly variable onset time. The difficulty in mitigating reduced visibility conditions caused by fog increases the severity of this impact. There is not a readily available source of data to examine the effects of potential impact mitigation, such as street lighting, warning systems, variable speed limit signs, or increased driver awareness programs. It is difficult to quantify the impact of reduced visibility directly. However, the indirect impacts of fog and reduced visibility provide additional insight into the hazard s impact on Dane County. Indirect Impacts Indirect impacts examine those costs which are associated with, but not directly caused by, fog. The increased number of automobile accidents during foggy conditions is an indirect 16 Dane County Local Hazard Mitigation Plan Data Collection Guide, Dane County 4.78

79 impact of fog. The higher damages of automobiles (which are damaged in the increased incidents of motor vehicle accidents) and the associated injury and death rates of the population in these events increase the magnitude of the indirect impacts from this hazard. The specific numbers for these impacts are available in the population and general property subsections of this profile. Impact Magnitude and Severity Summary The severity of fog events varies. In some cases, accidents attributed to fog may result in multiple fatalities and extensive vehicular property damage, meriting a catastrophic magnitude and severity rating. However, even though these events have a high fatality ratio (determined by the number of killed divided by the number of involved people), the percentage of the population involved in these events is usually minimal. Fog does not prevent facilities and services from operating and does not create undue strain on emergency response capabilities. Therefore, even though fog events may result in tragic situations, the magnitude/severity rating is moderate. Vulnerability Assessment Vulnerability is measured by examining the exposure of four categories to fog: Population, General Property, Essential Infrastructure, and Natural, Cultural or Historic Resources. In general, the greatest exposure to fog is population and general property, both of which are subject to increased incidents of damage (or injury and/or death, in the case of the population) as a result of poor visibility conditions associated with foggy conditions. This is particularly profound when examining traffic statistics. However, this is a small percentage of exposure compared to the overall contents of the County. Fog has a minimal exposure value on essential infrastructures, resources, and other types of general property. The fog itself is not dangerous- the indirect conditions fog creates are. Overall, Dane County has a low vulnerability to fog. Population Fog poses the greatest danger to people traveling, particularly on the highways of the County. Dane County s extensive highway transportation system includes three intersecting interstate highways, major federal and state highways, and County and local roads. These numerous heavily used major thoroughfares in Dane County constitute nearly 3,500 miles of roadway in the County. While people are not directly vulnerable to fog, the hazard greatly increases the danger of driving on the roads. The population is indirectly vulnerable, then, to the accidents and dangerous traveling conditions caused by the fog. Average weekday traffic on the Beltline Highway and Interstate 90 reached a volume of more than 84,000 in Average weekday traffic on the major arterials outside of the Beltline and I-90 reached a volume of more that 36,000 in In the time frame, over 3,000 accidents occurred in Dane County, when fog or smoke was present. Over 1,200 injuries were related to these accidents and 36 people were killed. 17 Overall, the population of the county has a medium vulnerability to fog. 17 Wisconsin Department of Transportation 2007 Wisconsin Traffic Crash Facts: Section 2, Crashes. Available online at last accessed March 3, Dane County 4.79

80 General Property Vehicles are the most vulnerable aspect of general property, as most accidents during fog are vehicle-to-vehicle. The Dane County Comprehensive Plan (Volume II) reports that Dane County residents own almost 350,000 personal vehicles. Although the number of accidents and deaths are considered indirectly related to the actual weather conditions, they far exceed the number of people killed due to tornadoes or floods for Dane County during this period. These accidents are considered indirectly related because law enforcement officials and the insurance industry assert that most accidents that occur in fog are the result of motorists following too close to the vehicle ahead of them and driving too fast for the weather conditions. The poor visibilities do not allow motorists to adjust when the vehicle in front stops or makes a quick turn. Fog also increases the vulnerability of those on water, and so boats may also be at a higher vulnerability but there is no data to examine this claim. Some property, such as businesses, homes, utility poles, or other objects located near roadways, may be vulnerable due to vehicle-object crashes impacted by the presence of fog, but there is not a quantifiable way to measure a heightened risk for non-vehicular general property. The overall vulnerability of general property is low. Essential Infrastructure, Facilities, and Other Important Community Assets The most vulnerable aspect of essential infrastructure for the community is the airport. The Dane County Regional Airport (DCRA) in Madison is the second largest airport in the State, providing service to commercial air passenger and cargo carriers, general aviation, and the military. Over 100 daily flights are provided on an average day. In 2006, 1.6 million passengers travel through the DCRA. Records of past incidents report cases of flight delays or cancellations at Dane County Regional Airport due to severe weather and fog. From June 2003 through November 2008, 3.8 percent of all delays into Truax Field were weather related. Nationally, more than 73 percent of all delays are weather-related. 18 These figures do not detail when National Aviation System delays are weather related. In 2007, airline delays cost approximately $8,089 million nationwide. 19 Generally, hospitals, command centers, fire and police stations, jails, schools, and other examples of essential facilities and infrastructures are not vulnerable to fog. The people employed at these institutions experience the heightened vulnerability discussed in the population subsection and emergency vehicles are theoretically subject to the same risks expressed in the general property subsection. However, out of 207,756 units involved in accidents in 2007, only 46 involved emergency response vehicles, or less than.03 percent. 20 Therefore, the vulnerability of emergency vehicles to traffic accidents is minimal, and the increased vulnerabilities attributed to fog are not measurable. The overall vulnerability of essential infrastructure is medium, due to transportation disruptions. 18 Research and Innovative Technology Administration, Bureau of Transportation Statistics, Airline On-Time Statistics and Delay Causes Available online at last accessed February 4, Air Transport Association, Cost of Delays Available online at last accessed February 4, Wisconsin Department of Transportation 2007 Wisconsin Traffic Crash Facts: Section 4, Vehicle Data. Available online at last accessed February 27, 200 Dane County 4.80

81 Natural, Historic and Cultural Resources These resources are not vulnerable to fog, excepting those located near roadways, as discussed in the General Property subsection of this profile. The overall impact of fog events on these resources is low. Estimating Potential Losses and Development Trends Assessment Potential Loss Estimates The vulnerability of motor vehicles to fog is difficult without quantitative data to determine the number of accidents caused by fog relative to all other traffic accidents. According to the 2007 Wisconsin Traffic Crash Facts, 10,255 accidents were reported in Dane County over the year. 46 of these accidents resulted in at least one fatality, while another 3,022 caused injury. Only Milwaukee reported more accidents on a County level. Statewide, 125,123 accidents were reported. 769 of these accidents occurred in fog (or similar condition) with 11 fatal accidents and 255 injury-causing accidents. These accidents were most likely to occur in dark, unlit areas (317). The road conditions were overwhelmingly wet (454). This indicates that 0.61 percent of accidents in Wisconsin are caused by foggy conditions. Applying this percentage to Dane County accidents in 2007, an estimated 62 vehicles were involved in car accidents during foggy conditions. There is no County-specific data available for the costs and damages of these car crashes, however crash reporting thresholds indicate that these crashes all caused at least $1,000 to any one person s property. 21 In addition, cost calculations used in the Crash Facts document assigned values of $1,249,000 for fatal accidents and an average of $32,300 for injury-causing accidents. Applied to the estimated number of accidents in Dane County, fog accounted for approximately $1,909,858 in damages in Economic losses from travel delays, both road and air, could be significant, but the costs and losses from those events is not systematically collected and compiled and thus difficult to estimate. Property, facilities, and natural, historic, and cultural resources are not vulnerable to fog, so their potential loss estimates are minimal. Development Trends Populations are considered indirectly vulnerable to fog due to the increased incidents involving traffic accidents; therefore as the population continues to grow, the likelihood of traffic accidents during foggy conditions also increases. Additional development of property will not change the vulnerability rating of the County to fog from a property standpoint. The development of urban areas with fog mitigation technology, including adequate street lighting or variable speed-limit signs, will reduce the exposure of the population and property to indirect impacts of fog. Increased public awareness of appropriate cautions to use in foggy conditions may help prevent an increased vulnerability of the population. 21 Wisconsin Department of Transportation 2007 Wisconsin Traffic Crash Facts: Section 1, General Highlights. Available online at last accessed February 27, Wisconsin Department of Transportation 2007 Wisconsin Traffic Crash Facts: Section 2, Crashes. Available online at last accessed February 27, 200 Dane County 4.81

82 Overall Risk Summary The overall risk for fog is medium. Fog poses no direct risk to the structures or facilities of Dane County, but contributes to fatal automobile accidents. The indirect impacts of fog are related to increased incidence of traffic accidents and travel delays. As demonstrated in the past history data, the occurrence of fog is common in Dane County. The numbers of auto accidents and flight delays where fog is a factor is available, but the costs and losses from those events is not systematically collected and compiled. Table 4.21 Overall Risk for Fog Measurement Rating Value Geographic Extent Extensive 3 Probability of Future Occurrence Highly Likely 4 Vulnerability Assessment Low 1 Impact Magnitude and Severity Moderate 2 Overall Risk Rating Medium Hail Hazard Profile Hail falls from thunderstorm clouds that extend miles high into extremely cold air. Updrafts bring raindrops from the bottom to the top of the cloud where they freeze into ice pellets. The pellets then fall only to be blown back up where another coating of rain freezes to the hailstone and it grows larger, layer by layer. This layering affect increases the size of hailstones, sometimes to the size of baseballs or grapefruits. Typically the stronger the updraft, the more times a hailstone repeats this cycle and consequently, the larger it grows. Once hailstones reach a weight sufficient enough to overcome the updrafts, they fall to the ground. Since the stone is not in the warm air below the thunderstorm long enough to melt before reaching the ground, it falls as ice. Dane County averages about 3 days with hail per year. The period of time with the most frequent occurrence of hail producing severe thunderstorms is May through September. Geographic Extent Hail falls in swaths ranging from miles long and 5-30 miles wide, and typically onehalf mile wide and five miles long. The swath is rarely a large, continuous bombardment, but generally consists of a series of hail strikes that are produced by individual thunderstorm clouds traversing the same general area. A single storm will produce several series of hail storms as it moves. The swaths may partially overlap but often leave completely undamaged gaps between them. 23 Given these facts, the geographic extent rating is significant. 23 Wisconsin Emergency Management. (July 2001). State of Wisconsin Hazard Mitigation Plan. Dane County 4.82

83 Past History The National Weather Service and the National Climatic Data Center (NCDC) maintains a listing of reported hail events, with a hail size greater than 0.75 inches, from 1950 through In Dane County, 111 hailstorms have been recorded since May of Of those storms, 53 percent created hail of.88 in diameter or larger. 7 incidents produced baseballsized hail or larger. The largest hail size ever recorded in the County was four inches in diameter in July of Hail events historically occur most frequently in June, July, and August, although hail has been reported with thunderstorms in every month of the year statewide. During the summer months there is over a 60 percent chance that a hail event will occur. July 7, 1991 Dane County received a presidential disaster declaration for damages resulting from a storm on July 7, Winds topping 80 mph, hail, rain, and lightning caused extensive damage in Dane County. The storm left 60,000 people without electricity and downed so many tree branches that it took weeks for clean up to be completed. Dane County Regional Airport was estimated as receiving $4-5 million in damages losing some planes completely and severely damaging others. Twenty buildings were also damaged at the airport. Local farms sustained $3.1 million in damages to crops and buildings due to hail and high winds. Two people were reported injured in Dane County. May 18, 2000 A supercell thunderstorm moved east/northeast across Iowa County. Hailstones up to 2.00 inches in diameter pelted and damaged many vehicles and home sidings, while stripping some of the corn and soybean crops. This storm then headed east into Dane County where it unleashed damaging straight-line winds in addition to large hail. Winds were estimated to reach hurricane-force level as the storm tore through Fitchburg where a home's garage was blown over. The storm then hit Madison with powerful winds and golf ball size hail. A Madison home's roof was torn off by the winds, and many large trees were felled. At least 200 vehicles sustained moderate to severe hail damage in Dane County. August 11, 2002 A cluster of severe thunderstorms blossomed over western Dane County, resulting in wind, hail, and flash flood damage in the Pine Bluff area, west of the Madison metro-area. In the Pine Bluff area, hurricane-force downburst winds reached estimated speeds of 70 kts (80 mph), resulting in toppled trees and power lines. The fringe effects of this powerful macroburst resulted in some tree damage north to the Cross Plains to Middleton area. The thunderstorm cluster also produced hail up to 2 inches in diameter in the Pine Bluff area, resulting in major damage to at least 100 vehicles, and to roofs and siding of homes. 24 April 13, 2006 A cluster of isolated severe thunderstorms hammered Dane County. Hailstones, some the size of tennis balls, hammered southern Wisconsin on Thursday night, denting cars and covering lawns as the storm moved west to east. The largest specimen, with a diameter of 24 National Climactic Data Center. (2003). Dane County 4.83

84 4.25 inches, was found in Jefferson County, said Darrin Hansing, a National Weather Service meteorologist. In southwestern Wisconsin, a weather service employee recorded 2.5-inch hail in Dodgeville around 9 p.m., and an Iowa County law enforcement officer saw hailstones 2.75 inches in diameter. In Madison, trained weather service spotters reported 2-inch hail on Fish Hatchery Road and 1.75-inch hail at West Towne Mall about 9:30 p.m. A few minutes later, other spotters reported 3-inch hail in Monona and Cottage Grove. Major damage was done to automobiles in Madison area. Homeowners suffered major damages as roofs and shingles were severely damaged by the hail. April 18, 2006 Severe storms, with large hail and damaging, straight-line, downburst winds, developed ahead and along a cold front, which plowed east into an unseasonably warm, moist airmass over southern Wisconsin. The hail stones ranged from 3/4 inch to 2 inches in diameter, resulting in several vehicles receiving dents (in Lafayette, Sauk, and Dane County). The damaging winds were mostly in the 60 to 70 mph range resulting in numerous reports of uprooted trees. Dozens of power lines were pulled down as broken tree branches fell on them. Probability of Future Occurrences The frequencies of past hail events provide a base line to predict the risk of future occurrences. Hail events are documented multiple times each year, and there are no climactic indications that these occurrences will change in the measurable future. Based on the past history of events, hail has a 100 percent chance of occurrence in a given year, which correlates to a highly likely occurrence rating. Impact Assessment While hail is usually a geographically isolated event, it is rarely isolated meteorologically. Hail almost always occurs in conjunction with a severe thunderstorm. Storms capable of producing large hail are also likely to produce lightning, high winds, heavy rain, and possibly tornadoes. Damages associated with these storms result from the combination of all of these factors. Insurance industry representatives involved in this planning effort indicate that a large hailstorm is one of their greatest concerns in terms of potential losses and insurance payouts. Hailstorms can cause extensive property damage in both urban and rural settings. Most hailstorms produce marble size or smaller hailstones, which can damage crops, but do not typically cause damage to automobiles or buildings. Larger hailstones can destroy crops and can cause extensive damage to buildings, including roofs, windows, and siding. Vehicles and even aircraft can be a total loss. When windows or roofs are damaged due to hail, water damage from often accompanying heavy rain can be significant. A major hailstorm can cause cumulative damages to crops and personal property running into the millions of dollars. Serious injury and loss of human life, however, are rarely associated with hailstorms. Dane County 4.84

85 No deaths or injuries have been directly attributed to hail in Dane County. According to the National Weather Service, financial losses due to hail are approximately $7.5 million in property damages since As a result, the impact assessment of hail is moderate. Vulnerability Assessment In general, all Dane County agricultural crops, buildings, and vehicles are to some degree vulnerable to hail damage. The essential functions of the critical facilities are not likely to be impacted by hail. Nor are any at-risk populations any more vulnerable than the general population. Table 4.22 summarizes the County s potential exposure to hail damage: Table 4.22 Property Vulnerable to Hail Damage Item Number Estimated Value Crops Corn for grain or seed (acres) 158,370 Varies Corn for silage (acres) 25,392 Varies Wheat (acres) 4,759 Varies Soybeans (acres) 87,185 Varies Forage (acres) 78,264 Varies Vegetables harvested for sale (acres) 2,446 Varies Residential improvements (parcels) $16,348,209,309 Commercial improvements (parcels) $6,291,971,200 Automobiles 350,000 Varies The numbers in Table 4.22 represent the total, cumulative value of property and crops that are exposed to the potential for damage or destruction due to hail. Damaging hail does not affect the entire County in one event. Hail is a geographically isolated event that affects only several square miles at any one time. In terms of crop losses, the actual damages that occur will depend on the type of crop and the growth stage of the plants when the hail occurs. In terms of property losses, the actual damages will depend on the housing density and density of automobiles in the impacted area. This is highly variable across the County. A storm with large hail over a crowded shopping mall on a Saturday afternoon will have a significantly different impact than the same storm over a suburban area in the evening when most of the cars are parked in garages. Likewise, a hailstorm in a rural area in the early spring when the plants are just emerging will have much less of an impact than a storm of the same intensity occurring later in the growing season when the plants are more susceptible to damage and when there is no time to replant if the crop is a total loss. These facts lead to a vulnerability assessment of medium. Potential Future Losses and Development Trends The potential for future losses due to hail damage is estimated based on an extrapolation of losses from past events. There are limitations to this method: Hail damage is not typically a meteorologically isolated occurrence. Damages occur in conjunction with high winds and heavy rain and storm damage estimates are usually Dane County 4.85

86 cumulative of all of these effects. The NCDC website provides data on only a handful of events where significant hail damage estimates are isolated from other causes. The exposure to damage increases as the population of the County increases. Future damages may increase simply due an increase in the amount of exposed property. The damages resulting from a hailstorm depend greatly on where and when the storm hits. The use of average losses from past events does not account very well for these variables. The NCDC database indicates that since 2003, Dane County has seen more than 37 hailstorms with hail size greater than.75 inches, ten occurrences with hail at least 2 inches in diameter, and six of those events causing over $7.6 million in reported damages. Using statistics and averages, based on the data collected in the NCDC database, an average correlation between hail damage and size can be extrapolated. The damage amount is cumulative, and drawn primarily on inference, as not all events reported a damage estimate. Therefore, this estimate is only a rough prediction of potential damage for any given hail event. In the last twenty years, the average size of hail falling in the County is 1.14 inches and the total reported damages to crops and property is about $8.1 million. Assuming that the damage was evenly distributed over the twenty year span, the average hailstorm is predicted to cause approximately $150,000 worth of damage. Overall Risk Summary Hail poses risk to the structures and facilities of Dane County, as well as automobiles. Hail s greatest threat is to agricultural commodities produced in Dane County. As demonstrated in the past history data, the occurrence of hail is common in Dane County. Since hail only affects small portions of the County at any one time, the overall risk for hail is medium. Table 4.23 Overall Risk for Hail Measurement Rating Value Geographic Extent Significant 3 Probability of Future Occurrence Highly Likely 4 Vulnerability Assessment Moderate 2 Impact Magnitude and Severity Medium 2 Overall Risk Rating Medium Landslides, Sinkholes and Erosion Description Landslides, sinkholes and erosion are geological phenomena that can pose a hazard to structures and people. Although none of these events are likely to cause a major natural disaster in Dane County, all three present some level of risk to the County s citizens. A landslide is a relatively sudden movement of soil and bedrock downhill in response to gravity. The movement of the soil can cause damage to structures by removing the support for the foundation of a building or by falling dirt and debris colliding with or covering a Dane County 4.86

87 structure. Landslides can be triggered by heavy rain, bank or bluff erosion, or other natural causes. 25 A sinkhole is a depression in the ground caused by an evacuation of support from below the soil. Sinkholes can form naturally in areas with karst geology areas that have limestone or other bedrock that can be dissolved by water. As the limestone rock under the soil dissolves over time from rainfall or flowing groundwater, a hollow area may form underground, into which surface soil can sink. Sinkholes also can be caused by human activity. Identifying areas with karst conditions is important, and not just for public safety and the protection of structures. Karst features provide direct conduits to groundwater. Areas with karst conditions can be subject to groundwater contaminants from pollutants entering a sinkhole, fissure or other karst features. 26 Erosion is the detachment and movement of soils or rock fragments by water, wind, ice or gravity. 27 Erosion may contribute to the likelihood and occurrence of landslides, particularly when stream banks or bluffs are eroded. The State Hazard Analysis from 2002 cites several examples where structures that were otherwise considered not vulnerable to landslides and flooding were endangered due to soil and streambank erosion. 28 Plans for regulating potential sources of erosion, including stormwater, streambank, farming, and construction sites, appears multiple times in the Dane County Comprehensive Plan (published in October of 2007) and indicates that mitigation efforts for erosion are ongoing. Geographic Extent According to the United States Geological Survey (USGS), Landslides occur in every state and U.S. territory. The Appalachian Mountains, the Rocky Mountains and the Pacific Coastal Ranges and some parts of Alaska and Hawaii have severe landslide problems. Any area composed of very weak or fractured materials resting on a steep slope can and will likely experience landslides. 29 In Wisconsin, landslides generally are not dramatic. However, there have been instances of bluff slumping along the shore of Lake Michigan, rock fall along the bluffs of the Mississippi River and the collapsing of hillsides during heavy rainfall. 30 Figure 4.18 indicates areas of landslide incidence and susceptibility. For Dane County, most of the land demonstrates both a low susceptibility and incidence. The southwest corner of the county demonstrates a moderate susceptibility and low incidence occurring, while a small portion just north of Madison demonstrates a high susceptibility and low incidence of occurrence. Steep slopes are another indicator of potential landslide problem areas, or areas that may have development constraints. Slopes greater than 12 percent are shown in Figure The map indicates a concentration of these slopes in the western County. Some parts of southern and western Wisconsin have experienced sinkholes from abandoned underground mines that have collapsed. 31 Areas with karst potential are indicated Figure 25 Wisconsin Emergency Management State Hazard Analysis November 2002 p 63. Available online at last accessed February 10, Ibid., p Dane County Department of Emergency Management, Dane County Flood Mitigation Plan July 2004 p Wisconsin Emergency Management, State Hazard Analysis November 2002 p 64. Available online at last accessed March 23, USGS Landslides Hazard Program: Landslides 101. Available online at last accessed February 10, Wisconsin Emergency Management State Hazard Analysis 2002 p Ibid., p 64. Dane County 4.87

88 4.19. The majority of Dane County demonstrates a deeper karst potential, which indicates that the process occurs deeper than five feet below the surface. There are scattered shallow karst potential regions in the southwest corner of the County, consistent with the landslide susceptibility mapping and the presence of the Driftless Area. The Driftless Area is primarily composed of southwestern Wisconsin, and portions of Minnesota and Illinois, categorized by the lack of glacial drift, or the deposits of debris left behind glaciers. Shallow karst potential indicates the potential for the karst process to occur anywhere between the surface and five feet below the surface. By contrast, significant portions of Dane County are susceptible to erosion, from a variety of sources. The extent of landslide susceptibility is more than 10 percent but less than 50 percent of the total county area, meriting a significant geographic extent rating. Karst geology is more widespread, covering at least 80 percent of the total county area and is thus rated as geologically extensive. A combined rating is reflected in the overall hazard rating at the end of the chapter. Figure 4.19 National Landslides Hazard Map Dane County 4.88

89 Source: USGS Landslides Hazard Program: Learning and Education Note: Susceptibility not indicated where same or lower than incidence. Susceptibility to landsliding was defined as the probable degree of response of [the area] rocks and soils to natural or artificial cutting or loading of slopes, or to anomalously high precipitation. High, moderate, and low susceptibility are delimited by the same percentages used in classifying the incidence of landsliding. Some generalization was necessary at this scale, and several small areas of high incidence and susceptibility were slightly exaggerated. Figure 4.20 Wisconsin s Shallow Karst Potential (Dolomite Bedrock) Source: Wisconsin Geological and Natural History Survey, Dane County 4.89

90 Figure 4.21 Slopes Steep Slopes - Greater 12% Dane County 4.90

91 Previous Occurrences The Town of Westport submitted the following previous events for landslides and erosion: During the initial development of the Waunakee Castle Creek neighborhood, there was a large mud slide off the hill which actually damaged some homes under construction along Manchester Crossing and along a drainage system currently in place. During heavy rains, farming practices utilized on a Westport farm located near the intersection of Division and Main resulted in a great deal of sediment flow directly across Division Street and into Six Mile Creek. There was also a great amount of sedimentation moving across Woodland Drive near Mill Road in Westport when the Waunakee Southbridge development was under construction. As of spring 2009 there is still significant water drainage from this area but it is not muddy or silty. During the construction of Bishops Bay on the north shore of Lake Mendota, in Westport, a large quantity of mud washed into the lake because several erosion control measures failed during a heavy rain. There have also been some minor slides into Lake Mendota from properties on the steep portions of the shoreline that were engaging in construction efforts. Other examples of landslides and sinkholes in the County are not detailed specifically, but are reflected in the numerous erosion controls and ordinances in the County. There are no documented occurrences of problems associated with sinkholes in Dane County available as of Probability of Future Occurrences There are not enough previous occurrences of landslides, sinkholes, or erosion to calculate a recurrence interval. Based on the absence of documented events, it is assigned a low occurrence rating. It is possible that these events may be occurring more frequently, but having little impact to existing development. Erosion events happen constantly as an ongoing geologic event, but damaging impacts occur less frequently. Impact Assessments Direct Impacts Direct impacts of these hazards impact essential infrastructure and natural resources primarily, with additional, but less severe, impacts on critical facilities and response capabilities. Landslides impact the integrity and navigability of roads, rail lines, and waterways by filling the passages with soil and debris. This impacts the direct usage of the transportation networks and creates secondary impacts on the movement of supplies and goods, including critical supplies such as medications and foodstuffs, between distribution points and commercial centers. Erosion directly impacts the ecology of the County, as discussed in the Comprehensive Plan. Hydrologic disruption gives rise to physical and ecological impacts as well. Enhanced runoff causes increased erosion from construction sites, downstream areas, and stream banks. The increased volume of water and sediment, combined with the flashiness of these peak discharges, result in wider and straighter stream channels. There is substantial loss of both streamside (riparian) habitat through erosion, and in-stream Dane County 4.91

92 habitat as the natural streambed of pebbles, rocks and deep pools are covered by a uniform blanket of eroded sand and silt. Loss of tree cover leads to greater water temperature fluctuations, making the water warmer in the summer and colder in the winter. 32 Landslides, sinkholes and erosion could impact the ability of response capabilities to navigate between areas. Population, general property, and cultural or historic resources are only impacted directly on a case-by-case basis, where a landslide, sinkhole, or erosion event directly strikes these specific areas. There is no quantifiable way to assess these incidentspecific impacts outside of actual occurrences. Examples may include sinkholes damaging structures or croplands, erosion changing previously protected structures into exposed properties for flooding, or landslides damaging physical properties. Indirect Impacts The indirect impacts of erosion augment the probability and likelihood of other hazards, including landslides and flooding. The effects on water ecology are also profound, but exceed the scope of this planning process. Chapter 5 of the Comprehensive Plan expands on these details. Landslides may indirectly impact the landscape, which may also have land use or recreational repercussions. Revenue losses are possible due to inaccessibility of affected areas, lost agricultural income due to field degradation, and loss income from natural resources such as parks and waterways due to contamination, damage, or destruction caused by landslides, sinkholes, or erosion. Magnitude, Severity and Impact Summary There are not significant reported incidents of landslides or sinkholes in the County, although the karst maps indicate that the potential for these events is present over a large geographic area. The karst maps also indicate that the geography of the County does not lend itself to catastrophic landslides or sinkhole scenarios. The anticipated severity of these events is relatively minor, as no documented injuries, deaths, impacts on essential facilities and services, or significant property damage has been reported. The significant efforts already in place to mitigate erosion by land use and erosion control ordinances reflect the progress of the County regarding erosion hazards. These measures indicate that erosion posed a very large hazard and/or water quality issue to the County, but is steadily being addressed and mitigated. For now, the overall magnitude, severity and impact rating is minor, both because of the lack of documented events and the large amounts of mitigation efforts already in place. These efforts must be continued, however, for the rating to remain low. Vulnerability Assessment The overall exposure of the County to landslides and sinkholes are difficult to quantify, as the events generally impact specific buildings or aspects of land and the predictability of those is variable. However, some attempt below is made to examine potential vulnerability for planning and mitigation efforts. Erosion potentially affects a greater number of properties and facilities, but it is also a heavily mitigated hazard within the County, as 32 Dane County Comprehensive Plan Vol. II, p 182. Dane County 4.92

93 demonstrated by the numerous zoning and erosion control ordinances. Overall, the average vulnerability assessment rating for these hazards is minor. Population In general, the population is not overly vulnerable to landslides, sinkholes or erosion except for specific and unpredictable incidents. For example, populations with vehicles are theoretically susceptible to sinkholes in roadways, but there is not a measurable means for examining this vulnerability. Thus the overall vulnerability of population is low. General Property General property is only vulnerable to landslides, sinkholes and erosion when it directly strikes the property. The County has several ordinances and controls in place to regulate the development and use of land to prevent most occurrences of erosion. There is not a standard means of examining vulnerability of general property to these hazards without better documentation of previous occurrences or mapping of hazard areas. The continued emphasis on zoning, smart growth community plans, and land use ordinances indicate that the County is pre-mitigating the potential for these hazards, rather than reacting to the hazards. The overall vulnerability rating for general property is low. Essential Infrastructure, Facilities, and Other Important Community Assets Dane County had over 43,842 acres developed for transportation usage as of An additional 6,800 acres were devoted to developed communication, utilities, institutional and governmental uses. Broadly, all of these areas are considered essential infrastructure or critical facilities of some kind. Transportation networks are the most exposed aspect of the County to erosion, landslide and sinkhole incidents because the associated impacts are highest. The loss of transportation networks could potentially cause secondary damage to the overall County s infrastructure, including revenue, transportation availability, emergency response mechanisms and other essential capabilities by preventing the means of these resources from activating or moving between locations. The vulnerability of the physical buildings and capabilities themselves are more like those outlined in the General Property section of this profile. Again, without more specific past occurrence incidents or hazard mapping, it is difficult to quantify the vulnerability of these facilities. The overall vulnerability rating is considered medium. Natural, Historic and Cultural Resources Natural resources are perhaps the most exposed element of the County to these hazards. Because landslides, sinkholes and particularly erosion directly impact the geographic makeup of the County, and the associated ecology, these hazards primarily directly impact the natural resources of the County. Historic and Cultural resources experience a vulnerability rating similar to that of General Property, where data and assessments rely more on specific occurrence than a generalization of the event. Overall, because of the potential impacts on natural resources, the vulnerability rating is medium. Estimating Potential Losses and Development Trends Assessment Potential Loss Estimates There is little data to base a future loss estimate on for these hazards. Generally, the anticipated loss is expected to be limited. This is largely due to the fact that the areas Dane County 4.93

94 potentially at risk (southwest Dane County) are also the least developed areas of the County. Development Trends Development pressures in Dane County have potential to increase the problems associated with landslides, sinkholes, and erosion, but these impacts can be mitigated by wise land use planning. Construction is consistently cited as a source of erosion, and poorly engineered fill can become landslide hazards. The expansion of the population continues to infringe on natural wetlands and natural landscapes, which increases the potential of erosion and groundwater depletion. As groundwater tables continue to fall, the potential for sinkholes increases. Landslides can often be mitigated by avoiding steep grading in development areas. Overall Risk Summary As noted in the hazard description, neither landslides, erosion, nor sinkholes are likely to be the cause of a major natural disaster, and thus the overall risk rating is low. However, there is the potential for these hazards that should be considered in land use practices and decisions. This section should be reviewed and updated as more data becomes available. Table 4.24 provides the summary for how all aspects of the hazard profile were evaluated to establish an overall hazard rating. Table 4.24 Risk Summary for Landslides, Sinkholes, and Erosion Measurement Rating Value Geographic Extent Significant 3.0 Probability of Future Occurrence Low 1.0 Vulnerability Low 1.0 Impact Magnitude and Severity Minor 1.0 Summary Risk Rating: Low Lightning Description At any given moment, there are 1,800 thunderstorms in progress somewhere on the earth. This amounts to 16 million storms each year. Lightning detection systems in the United States monitor an average of 25 million strokes of lightning from the cloud to ground every year.. According to the Vaisala Group, an average of nearly 300,000 cloud-to-ground strikes hit Wisconsin each year based on data from 1996 to Lightning is caused by the attraction between positive and negative charges in the atmosphere, resulting in the buildup and discharge of electrical energy. This rapid heating and cooling of the air produces the shock wave that results in thunder. During a storm, raindrops can acquire extra electrons, which are negatively charged. These surplus electrons seek out a positive charge from the ground. As they flow from the clouds, they knock other electrons free, creating a conductive path. This path follows a zigzag shape that jumps between randomly distributed clumps of charged particles in the air. When the two charges connect, current surges through that jagged path, creating the lightning bolt. Each spark of Dane County 4.94

95 lightning can reach over five miles in length, soar to temperatures of approximately 50,000 degrees Fahrenheit, and contain up to 100 million electrical volts. 33 Geographic Extent Lightning can occur anywhere. All thunderstorms create lightning, and lightning may strike as far as 10 miles away from a thunderstorm. 34 The geographic extent of lightning is global, and therefore is usually classified as extensive. The available data regarding lightning events in Dane County further supports this rating, as no region of the county demonstrates an immunity or lower percentage of occurrence than another. However, lightning strikes that cause problems are typically isolated incidents, thus the classification of isolated is assigned. Figure 4.23 indicates the density of lightning strikes by County in the United States, normalized by population density and implies lightning strike risk level relative to other areas of the country. According to this map, no portion of Wisconsin experiences high flash density. However, relative to the rest of the state of Wisconsin, Dane County falls in the region that experiences the most lightning flash density. This information is further supported in Figure 4.22, which depicts the number of lightning strike events, including associated deaths and injuries, for the entire state of Wisconsin by county. However, Wisconsin lightning data in Figure (a) is not complete and is based only on newspaper reports. Some lightning incidents are not reported in newspapers. Nonetheless, according to this information, Dane County experiences the second highest number of lightning strikes in the state. Previous Occurrences From a national perspective, Wisconsin has a moderate to moderately high risk to lightningrelated injury, death and property damage. Wisconsin ranked 28th in the nation for most lightning-related casualties in the period between 1990 and 2003, with 12 reported deaths. Between 1959 and 1994, Wisconsin residents sustained 194 injuries and ranked 16th in the nation for property damage, with more than 500 reports of damage. Actual dollar losses are not specified NOAA, Lightning Safety. Available online at last accessed on February 9, FEMA, Thunderstorms and Lightning Available online at last accessed on February 5, National Lightning Safety Institute, Lightning Fatalities, Injuries and Damage Reports in the United States, Available online at last accessed February 9, Dane County 4.95

96 Figure 4.22 Lightning Events for Wisconsin ( ) Source: National Weather Service Dane County 4.96

97 Figure 4.23 Lightning Flash Density for the United States Dane County 4.97

98 Statistics for Dane County are reflected in the risks of the state. Between 1995 and 2008, 40 lightning strikes have occurred in Dane County where damage to person or property has occurred. One death occurred in August 2007 and 10 people have sustained injury over this period. Lighting caused an estimated $1.8 million in property damages between 1995 and As an example, the NCDC database records a single thunderstorm passing through Dane County on August 2, 2001 that started 5 house fires in 5 different communities. The NCDC database records severe storms that result in lightning damage. A selection of these events is listed below. July 6, 2003 Lightning struck a home in Middleton, resulting in a roof/attic fire. August 22, 2007 A thunder storm lightning strike to a utility pole caused a live wire to fall in a puddle of water at a bus stop as people were getting on a bus in Madison. Three people were killed and a fourth was injured. August 27, 2007 A man playing golf Monday in Madison died after he was hit by lightning. The golfer sought shelter from the rain under a pine tree but was struck anyway. This was the second deadly incident caused by a lightning strike in Madison in a week. Probability of Future Occurrences Lightning events in Dane County show no indication of lessening. Though records on the NCDC database are only available since 1996, severe thunderstorms are documented back into the 1800s. Since all thunderstorms produce lightning of some kind, it is reasonable to assume that lightning strikes have also always occurred in Wisconsin. Using the formula established in Section Profile Methodology, the assessment reflects (42 events over [divide by] 12 years) x 100 = 100 percent chance of occurrence and a highly likely future occurrence rating. This occurrence information is drawn from the NCDC database for lightning events in Dane County. Impact Assessment Direct Impacts Lightning follows the shortest, easiest path to earth and often follows several paths simultaneously. Lightning strikes buildings or other objects because the materials in them provide easier paths to the ground than the air. Lightning is more likely to strike on projecting objects such as trees, poles, wires or building steeples than on large, flat surfaces located at the same height or lower. Lone buildings are also primary targets. Lightning can enter a building through a direct strike, by striking a metal object attached to the building, by leaping over to the building after striking a nearby tree, or by following a power line or ungrounded wire fence attached to a building. Dane County 4.98

99 Lightning is often perceived as a minor hazard. The effects of lightning, however, can be significant, causing property damage, injury, and death. Damage from lightning occurs in four ways: Electrocution, severe electrical shock, and burns of humans and animals Vaporization of materials in the path of the strike Fire caused by the high temperatures associated with lightning Power surges that can damage electrical and electronic equipment When humans are struck by lightning, the result is deep burns at the point of contact (usually on the head, neck and shoulders.) Approximately 70 percent of lightning survivors experience residual effects such as vision and hearing loss or neuropsychiatric issues. These effects may develop slowly and only become apparent much later. 36 Death occurs in 20 percent of lightning strike victims. Nationwide, 85 percent of lightning victims are children and young men ages engaged in recreation or work. 37 Indirect Impacts Lightning strikes cause intense but localized damage. In contrast to other hazards, lightning does not cause widespread disruptions with the community. Structural fires, localized damage to buildings, damage to electronics and electrical appliances, and electrical power and communications outages are typical consequences of a lightning strike. Additionally, indirect fatalities may result via electrocution when a person steps from a vehicle into standing water that was previously charged by a live power-line that was knocked loose by a lightning strike. The indirect social and economic impacts of lightning damage are typically associated with the loss of electrical power. Since society relies heavily on electric power, any disruption in the supply, even for a short time period, can have significant consequences. The utilities supplying Dane County have worked closely with emergency response agencies and human services providers to develop plans for responding to planned and unplanned power outages in the County. While Dane County has a generally low vulnerability to wildfires (see Section Wildfires for more information), they could be an indirect result of a lightning strike. Impact Magnitude and Severity Summary Based on the above direct and indirect impacts the overall magnitude and severity rating is considered moderate: 5 to 10 percent of property severely damaged, and/or facilities are inoperable or closed for more than a week percent agricultural losses. Fatalities possible but most injuries/illnesses are treatable and do not result in permanent disability. Minor indirect impacts. Vulnerability Assessment Population While national data shows that lightning causes more injuries and deaths than any other natural hazard except extreme heat, there doesn t seem to be any trend in the data to 36 FEMA, Thunderstorms and Lightning 37 National Lightning Safety Institute, Lightning Costs and Losses from Attributed Sources Dane County 4.99

100 indicate that one segment of the population is at a disproportionately high risk of being directly affected. Anyone who is outside during a thunderstorm is at risk of being struck by lightning. Aspects of the population who rely on constant, uninterrupted electrical supplies may have a greater, indirect vulnerability to lightning. As a group, the elderly or disabled, especially those with home health care services relying on rely heavily on an uninterrupted source of electricity. Resident populations in nursing homes, Community Based Residential Facilities, or other special needs housing may also be vulnerable if electrical outages are prolonged. If they do not have a back-up power source, rural residents and agricultural operations reliant on electricity for heating, cooling, and water supplies are also especially vulnerable to power outages. These populations are summarized in Chapter 4.3 General Property According to the event details collected in the NCDC database, the majority of reported damages from lightning are fires to private structures, damage to chimneys or steeples, or small grass fires. Property is more vulnerable to lightning than population because of the exposure ratios. Buildings remain exposed. Mitigation techniques such as choice of building materials or landscaping help reduce the vulnerability of these properties, but there is not data available to segment these properties out of the overall vulnerability assessment. Essential Infrastructure, Facilities, and Other Important Community Assets Some essential infrastructures and facilities can be impacted by lightning. Emergency responders, hospitals, government services, schools, and other important community assets are not more vulnerable to lightning than the general vulnerabilities established for property and population. Some aspects of infrastructure are constructed of materials and/or located in places that increase their vulnerability to lightning. Sometimes, communications and infrastructure are interrupted by lightning strikes. These events raise the vulnerability of the essential functions by delaying response times, hindering interagency communication efforts, or endangering or damaging communication networks. Natural, Historic and Cultural Resources There are no indications that cultural or historic resources are more vulnerable to lightning than as previously accounted for as general structures. Natural resources may be vulnerable to indirect impacts of lightning, such as wild fires caused by lightning strikes. The presence of large areas of water, or of wide, open spaces in natural habitats may increase the danger of lightning strikes to trees, people, or structures, but these vulnerabilities are not directly related to natural resources. Campgrounds are areas where lightning strikes have more dangerous impacts, so populations utilizing the campgrounds may have a higher vulnerability. Estimating Potential Losses and Development Trends Assessment Potential Loss Estimates The potential for future losses due to lightning damage is estimated based on an extrapolation of losses from past events. There are limitations to this method: The exposure to damage increases as the population of the County increases. Future damages may increase simply due an increase in the amount of exposed property. Dane County 4.100

101 The damages resulting from lightning depend greatly on where and when the storm hits. The use of average losses from past events does not account very well for these variables. Indirect impacts are not accounted for. While the estimation of future losses based on past events is unsophisticated, it still is a useful method of quantifying the damage potential. The NCDC database indicates that between 1996 and 2008, Dane County has experienced 40 lightning events where property damage, personal injury or death has occurred. According to the NCDC damages total $1.8 million, injuries total 8, and one direct fatality. Lighting was indirectly responsible for 3 deaths and one injury in Based on this history and assuming the losses could be proportionately spread over each incident, the estimated average loss per lightning strike event that causes damage is $45,000. Dane County averages 3.2 damaging strikes a year since 1996, which equates to an averaged annualized loss estimate of $145,000. Injuries occur every 1.5 years on average, and deaths every 12 years. Development Trends The development of residential areas with parks and open spaces may increase the likelihood of exposed populations occupying those spaces, which in turn raises the vulnerability of the general population. Dane County s population is growing, which increases the number of people exposed to lightning during a given event. The development of commercial and industrial sectors will minimally impact the vulnerability of the County to lightning. Development plans for more open parks and natural resource protection grounds may increase the potential for exposed populations. Overall Risk Summary Based on the previous assessments, the overall risk rating for lightning is medium. Table 4.25 provides the summary of all aspects of the hazard profile that were evaluated to establish an overall hazard rating. Table 4.25 Overall Risk for Lightning Measurement Rating Value Geographic Extent Isolated 1 Probability of Future Occurrence Highly Likely 4 Vulnerability Assessment Medium 2 Impact Magnitude and Severity Moderate 2 Overall Risk Rating Medium Extreme Cold/Wind Chill Description Typically, extreme cold temperatures (cold waves) in Wisconsin are accompanied by an active wind that results in an additional wind chill factor. This combination is especially hazardous when temperatures are at least 20 degrees below normal (National Weather Service communication) during the winter season. Dane County 4.101

102 Extremely cold temperatures present a variety of problems and impact the population of Dane county both directly and indirectly. Extreme cold is a dangerous situation that can bring on health emergencies in susceptible people, such as those without shelter or who are stranded, or who live in a home that is poorly insulated or without heat. Additionally, extreme cold/wind chill affects agriculture, industry, commerce, and social activities. Extremely cold temperatures may precede, accompany, or follow a winter storm or it may occur during otherwise typical weather conditions. What constitutes extremely cold temperatures varies across different areas of the United States, based on normal climate temperatures for the time of year. In Wisconsin, cold temperatures are normal during the winter. When temperatures drop at least 20 degrees below normal winter lows, the cold is considered extreme and begins to impact the daily operations of the county. Extreme cold/wind chill impacts inanimate objects, plants, animals and water supplies. Wind-Chill The effects of extremely cold temperatures are amplified by strong to high winds that can accompany winter storms. Wind-chill measures how wind and cold feel on exposed skin and is not a direct measurement of temperature. As wind increases, heat is carried away from the body faster, driving down the body temperature, which in turn causes the constriction of blood vessels, and increases the likelihood of severe injury or death to exposed persons. Animals are also affected by wind-chill however cars, buildings, and other objects are not. In 2001, the National Weather Service updated the wind-chill temperature index to take advantages of advances in science and computer modeling technology. Wind-chill effects are shown in Figure 4.24, highlighting the dangers of wind-chill to exposed individuals. For Southern Wisconsin, including Dane County, the National Weather Service issues Wind Chill Advisories when wind chill values are expected to range from -20 to -34. A Wind Chill Warning is issued when wind chill values are expected to be -35 or lower. For all of Wisconsin, the National Weather Service issues a Wind Chill Advisory when wind chill values are expected to be in the -20F to -34F range (a Cold/Wind Chill documented event in the Storm Data publication), and Wind Chill Warnings for wind chills of -35F or lower (an Extreme Cold/Wind Chill documented event in the Storm Data publication). Dane County 4.102

103 Figure 4.24 Wind-Chill Factors Source: National Weather Service Geographic Extent Extreme cold/wind chill is generally a regional phenomenon and Dane County is uniformly impacted when it occurs. Therefore, it is considered to have an extensive geographic impact rating. Wind-chill impacts the county with the same variability expected in high-wind disasters. One part of the county may experience significantly colder wind-chill than another, but the movement of the wind also drives the hazard from one location to another. Theoretically, then, the entire county may be impacted by the same hazard at different times. However, because of the variability of wind, the hazard is classified as having a significant geographic impact rating. When the two ratings for the variables within the hazard profile are combined, the overall geographic extent of the hazard is extensive. Previous Occurrences The data available on extreme cold/wind chill is limited. A search of data held by the Wisconsin State Climatology Office (SCO) provided observed maximum and minimum temperatures in Madison for every day from January 1, 1971 to December 31, This data, however, does not indicate wind-chill, nor does it provide any information regarding the impact of severe cold events. The data does provide baseline data for the recurrence interval of such events. Table 4.26 is a summary of the temperature extreme data from the SCO from 1971 through 2008, showing for each month, the number of days with low temperatures less than -10º F. Dane County 4.103

104 Table 4.26 Number of Days Below -10º F Month/Year Number of Days Month/Year Number of Days Month/Year Number of Days January 1971 February 1971 January (3 below 20) 5 (1 below 20) 7 (1 below 20) January 1979 February (4 below 20) 8 (2 below 20) February December February January February February January 1994 December January (3 below 20) February (5 below 20) 6 (1 below 20) February February January December February February 1996 January December (3 below 20) 6 (4 below 20) January February January January 1999 February January 1985 January February 1985 February (1 below 20) December January 1986 January (2 below 20) February January (2 below 20) 6 (4 below 20) 3 (1 below 20) December February December February (1 below 20) February January January (1 below 20) December February January January (1 below 20) February Source: Wisconsin State Climatology Office Website The National Weather Service and the National Climatic Data Center (NCDC) tracks weather extremes and the related consequences in greater detail. A search of the NCDC website provided the following descriptions of several extreme cold/wind chill and wind-chill events since These accounts are edited and annotated to reflect only Dane County information. January 13, 1994 An extended period of extremely cold weather gripped the state. Brisk winds at times combined with record setting sub zero temperatures down to 50 below zero at night to Dane County 4.104

105 create wind-chill readings to 80 below zero. During the cold spell numerous schools closed for days at a time, businesses reduced hours, sporting events, winter fest activities, and local government meetings were cancelled. Also many water mains broke and vehicles refused to start. Some people received frostbite and suffered from hypothermia. Heat and power failed in many homes, businesses, and schools. Natural gas and heating oil was consumed at record levels. December 9, 1995 Bitter-cold arctic air swept into Wisconsin on northwest winds of 20 to 40 mph. Temperatures dropped as much as 15º F in 15 minutes as the strong front moved through. Wind-chill values ranged from -25º F to -50º F. Hypothermia was a secondary cause (indirectly-related) for one death in Dane County. Many schools canceled evening activities, and retailers across the state reported very little shopping activity in spite of the upcoming Holidays. The AAA Club (3,000 calls) and service stations were overwhelmed with requests for assistance with stalled vehicles. There was also a scattering of frozen water pipes that resulted in flooded rooms or basements. At least six frozen water pipe incidents were noted in Dane County. January 30 February 4, 1996 After the previous day's ground blizzard, very cold arctic air poured into Southern Wisconsin on northwest winds of 10 to 25 mph. Wind-chills ranged from -35º F to -45º F. Overnight lows across Southern Wisconsin ranged from -5º F to -15º F. Arctic air continued to pour into Southern Wisconsin on northwest winds of 10 to 20 mph overnight. Morning lows dipped to -21º F in Madison. Wind-chills dropped into the -40º F to -60º F range as daytime temperatures never recovered to zero. Service stations were overwhelmed with calls for assistance, and hardware stores reported a booming business due to the demand for space heaters, snow blowers, and other cold-weather gear. The episode, continued through the first four days of February across south-central and southeast Wisconsin. Ending on the 4th, Madison registered 177 hours below the zero mark. Adding to the misery, wind-chills were in the minus 35º F to minus 60º F range many times during this event. Numerous water main pipes burst, and fiber optic cables froze disrupting telephone service. Schools were closed on the 2nd, and 8,000 homes in Southeast Wisconsin lost electrical service on the 2nd as power companies cut back on output. Service stations and the AAA were overwhelmed with requests for assistance. A new minimum temperature record of -29º F in Madison (now the February record) was set the 3rd. January 17, 1997 The coldest arctic air of the winter season enveloped southeast and south-central Wisconsin, resulting in many school closings and cancellation of evening activities. Maximum temperatures only reached zero in Madison, roughly 20 degrees below normal. Morning lows ranged from -7º F to -14º F. Coupled with northwest winds of 10 to 20 mph, wind-chills dropped to -30º F to -50º F. January 5, 1999 The combination of an arctic high pressure ridge, a fresh, deep snow cover, clear skies, and light winds allowed temperatures to plunge to well below zero across south-central and southeast Wisconsin. Observed minimums include Stoughton -23º, and -21º F in Madison. Dane County 4.105

106 Thousands of calls to local AAA and car service centers were logged due to stalled vehicles. Maximum temperatures were only around zero. December 18, 2005 The second cold snap of December 2005 was a contributing or secondary factor (indirect) in the death of a homeless man in Milwaukee. Media news reports indicated that some water pipes (outside faucet) froze on some homes across south-central and southeast Wisconsin. The average temperature across southern Wisconsin for the first 19 days of December 2005 was the coldest since the Across southern Wisconsin on December 18-19, 2005, maximum air temperatures were only in the teens and lows were around zero to 5 below zero, resulting in daily means around 15 to 17 below normal. In addition, cold temperatures occurred during the period of December 6-8, 2005, when daily means were around 20º F below normal (maximum temperatures in the teens and lows of zero to 10 below zero). February 3, 2007 The coldest air and lowest wind-chills of the winter season affected south-central and southeast Wisconsin as a massive arctic high pressure pushed southeast through the Western Great Lakes Region over the 4-day period of February 3-6, Minimum air temperatures tumbled to -5F to -14F on February 3rd with Madison's Truax Field registering -11º F on the 3rd. Daytime maximum air temperatures on the 3rd ranged from 3º F to 10º F. Early morning low temperatures on the 4th ranged from -10º F to -15º F. Afternoon maximum temperatures on the 4th never reached the zero mark, totaling -3º F at Madison. The lowest minimum temperatures of the 4-day period occurred on February 5th. Maximum afternoon temperatures on the 5th ranged from -4º F to 6º F. On February 3rd and 4th west to northwest winds generally clocked at 15 to 30 mph, which generated wind-chill values of -20º F to -30º F. Lower wind speeds of 5 to 20 mph were noted on February 5th and 6th. In general, the lowest wind-chill values were observed during the early morning hours on February 5th, in the -30º F to -34º F range, corresponding to the lowest air temperatures of the winter season. The cold temperatures resulted in a broken water main and electrical outage in the 100 block of West Main St. near the Madison Capitol Square early Saturday morning, February 3rd. Many public and private schools were closed on Monday and Tuesday, February 5th and 6th. It was the first time in 13 years that the Madison schools closed due to cold temperatures. Additionally, newspaper reports indicated that plumbers answered numerous frozen-pipe calls. March 27, 2007 On March 27th, a large sink hole developed on State Street in Madison due to a large water main break. This was the 117th water main break in the city of Madison for March, Usually there is only about 6 to 12 in some of the rougher winter months. Very cold temperatures and little snow cover in the first part of March, 2007, allowed the ground to freeze deeper. Subsequent freeze-thaw periods forced the ground under streets to shift/move, resulting in the numerous water main breaks. Damage was estimated at $300,000. January 15, 16, 2009 Arctic air blanketed southern Wisconsin and kept temperatures bitterly cold for a 48 hour period. Wind chills reached -35 to -45 F and actual temperatures briefly touched -30 F. All 16 school districts in Dane County cancelled classes, as well as the University of Wisconsin. Dane County 4.106

107 Compounding the problem were very slick stretches of road and intersections. Snowfall of almost two inches covered the icy patches making already slippery roads even more dangerous. Road crews worked around the clock to apply sand and salt, but the bitterly cold temperatures rendered the salt virtually useless. Dozens of cars and trucks were involved in slide offs, rollovers, and fender benders on area streets and highways. Probability of Future Occurrences Historical data indicates that extreme cold/wind chill is an annual occurrence in Dane County, and there are no climactic indications that the hazard will decrease in the measurable future. Using the formula established in Section Profile Methodology, the assessment reflects (13 events over [divide by] 9 years) x 100 = 100 percent chance of occurrence and a highly likely occurrence rating. Impact Assessments Direct Impacts Direct impacts are rated based on the actual affect of extreme cold/wind chill on the category being evaluated. The major impact of extreme cold/wind chill is frostbite and hypothermia. Frostbite occurs when the blood flow to the body diminishes enough to prevent adequate heating, and the flesh begins to freeze. It generally begins in the extremities (fingers, toes, tips of ears and nose) and, if untreated, can lead to permanent damage or the loss of limbs. Hypothermia occurs when the body s core temperature drops below minimum sustainability levels and key organs begin to fail, which can also lead to permanent injury or death. The longer the event lasts, the higher the risk of these vulnerable populations becomes. A study issued in December of 2008 indicates that extreme cold/wind chill is the second-highest cause of death in natural disasters. 38 This study is refuted by another article which examines death certificates (noting the medical cause of death) for the same time period. This essay finds that extreme cold/wind chill is the number one cause of death during natural disasters. 39 The CDC also recognizes the hazards of extreme cold/wind chill and offers resources targeted at individuals and families to mitigate the effects of extreme cold/wind chill, however, it provides no specific data for analysis. Indirect Impacts Indirect impacts examine those costs which are associated with, but not directly caused by, extreme cold/wind chill. For example, the loss of revenue to retail businesses as a result of persons staying indoors during extreme cold/wind chill events. Since very little data is collected on these indirect impacts it is difficult to make a statistical estimation of severity. Impact Magnitude and Severity Summary The impact magnitude and severity ratings for the population borders between critical and catastrophic based on the average yearly fatalities caused by extreme cold/wind chill. However, while the percent of population affected is not specifically outlined in the 38 Kevin A. Borden and Susan L. Cutter, Spatial Patterns of Natural Hazards Mortality in the United States appearing in the International Journal of Health Geographics 7:64 (2008). Available online at last accessed March 4, Indur Golklany, The Deadliest U.S. Natural Hazard: Extreme Cold. Available online at last accessed March 4, Dane County 4.107

108 magnitude/severity rating scale, it must be assumed that while the population does experience some fatal or permanent injury events, the majority of the population is not unduly exposed to the hazard. The impact magnitude and severity of the hazard for the majority of the population is moderate. The magnitude and severity of the hazard on property, critical infrastructure and natural, cultural and historic resources is also moderate. Overall a moderate magnitude/severity rating is most appropriate for the extreme cold/wind chill hazards. Vulnerability Assessment Population While everyone is vulnerable to extreme cold/wind chill events, some populations are more vulnerable than others. Extreme cold/wind chill pose the greatest danger to outdoor laborers, such as highway crews, police and fire personnel, and construction. The elderly, children, people in poor physical health, and the homeless are also vulnerable to exposure. Overall, the population has a medium exposure to severe cold. General Property Extreme cold/wind chill presents a minimal risk to the structures of Dane County. Property damage occurs occasionally when water pipes freeze and break. Homes without adequate insulation or heating may put owners at a higher risk for damages or cold-related injury. In cases of periods of prolonged cold, water pipes may freeze and burst in poorly insulated or unheated buildings. Vehicles may not start or stall once started due to the cold temperatures and the risks of carbon monoxide poisoning or structure fires increases as individuals attempt to warm cars in garages and use space heaters. Stalled vehicles, or those that fail to start, may result in minor economic loss if individuals are unable to commute between work, school, and home. Driving conditions may deteriorate if extreme cold/wind chill prolongs icy road conditions, which will impact commutes and emergency response times as well. Landscaping and agricultural products may be damaged or destroyed by unseasonable occurrences of extreme cold/wind chill, causing plants to freeze and die. This may increase the indirect vulnerabilities to severe cold by causing greater economic costs and losses for the year. The overall vulnerability of general property is low. Essential Infrastructure, Facilities, and Other Important Community Assets Like general property, extreme cold/wind chill events have a limited impact on the physical property of essential infrastructures and facilities. Communications lines such as fiber optic cables can freeze. There may be incidents of delayed emergency response due to stalled vehicles, delays in dispatching due to frozen communications lines, or an increased volume in calls. Hospitals may see an increase in cold-related injuries directly or injuries associated as secondary effects of the cold (traffic accidents, broken bones or severe cuts due to slips, etc.) and a prolonged extreme cold/wind chill event may impact hospital personnel capabilities. Personnel working in the cold, such as firefighters, EMTs, police officers and construction workers, have a higher vulnerability due to exposure times, and response capabilities may be hindered. Human services programs that care for at-risk individuals and families may be stressed, but usually can still adequately provide services through the duration of the extreme cold/wind chill event. Unusually high volumes of individuals seeking shelter or food may overwhelm some facilities if the event is prolonged. There may be an increased number of displaced individuals or families due to flooding caused by ruptured pipes, which may strain local aid organizations such as the Red Cross. If the event is extremely extended and impacts multiple other counties and states, which in turn impacts Dane County 4.108

109 the availability of mutual assistance, the risk factors may increase. The overall vulnerability of essential infrastructure is medium. Natural, Historic and Cultural Resources Natural and cultural resources such as campgrounds, lakes, state, county and national parks, and other outdoor venues may suffer vegetative or structural damage from extreme cold/wind chill with the same risks as those outlined in general property. The indirect impacts may increase the vulnerability of these resources to economic loss, as the attendance of outdoor venues in severe cold lessens. Older venues or historical properties suffer the same vulnerabilities associated with private and general properties that are older, with the added vulnerability of damaging historic and often irreplaceable property in the process. The overall vulnerability of these resources is medium. Estimating Potential Losses and Development Trends Assessment Potential Loss Estimates Property losses due to extreme cold/wind chill are typically minor and isolated. Direct impacts such as water breaks, which may cause water and flooding damage to structures and their contents, are the most likely source of potential property losses. Insurance claims are a potential source of information to verify these numbers, but they were not available for the 2009 update of this plan. There is no reliable data on the county level to quantify the monetary losses associated with critical facilities or infrastructure, but the potential losses to critical facilities is considered minimal. Potential loss of life and injury due to extreme cold/wind chill is difficult to estimate. Based on statewide severe weather statistics (from Table 4.1), severe cold accounts for 13 percent of all deaths related to severe weather hazards in the state. One method is to examine the number of hospital admissions in a given year for cold-related injury or circumstance, and find the percentage of fatalities from these specific admissions causes. Data from local hospitals was collected on cold-related injuries and deaths in Dane County from There have been more than 130 admissions of patients as a result of extreme cold/wind chill, with 8 fatalities. These numbers indicate that approximately 6 percent of all coldrelated injury admissions to a hospital will result in death. This averages out to roughly 8 extreme cold/wind chill injuries per year, with one death occurring every 1.8 years in this 15 year period. The affected population based on the hospital data was about equal for ages 15 to 24, ages 45 to 54, and ages 75 and above. This belies the assumption that the elderly are more at risk than other population groups. Other than hospitalization records and rough estimates drawn from emergency personnel dispatch records, there are not data sources to further quantify the losses. Development Trends New buildings are at a lower risk for indirect damage due to severe cold through utilization of better building materials and insulations. Newer construction may actually decrease the vulnerability of the population it shelters to extreme cold/wind chill, as newer materials and construction techniques may increase the heating effectiveness of residential or commercial facilities. As the population continues to grow and age, the at-risk population will continue to grow as well. There is no current indication that the increasing population will change the overall chance of an exposure-related death in Dane County, however the possibility must be considered. Additional health care facilities or human services locations for at-risk populations will face the same risk levels as existing structures. Public education remains Dane County 4.109

110 the primary means of mitigating the risks of extreme cold/wind chill, both to the population and for property protection. Overall Risk Summary Overall, extreme cold/wind chill presents a high risk for Dane County. The events occur frequently and over significant portions of the county, maximizing the exposed population. While the impacts on structures and the environment are minimal, there are still reports of damage. The ability to quantify these assessments is not currently available, as no accurate financial data for damages incurred exists. Table 4.27 provides the summary of how all aspects of the hazard profile were evaluated to establish an overall hazard rating. Table 4.27 Overall Risks for Extreme Cold/Wind Chill Measurement Rating Value Geographic Extent Extensive 4.0 Probability of Future Occurrence Highly Likely 4.0 Vulnerability Assessment Medium 2.0 Impact, Magnitude and Severity Moderate 2.0 Overall Risk Rating High Excessive Heat Description Excessive heat during the summer season is characterized by a combination of very high temperatures and exceptionally humid conditions. Humid or muggy conditions, which add to the discomfort of high temperature, occur when a dome of high atmospheric pressure settles over the southern part of the country and pulls hot, muggy air north into Wisconsin. The National Weather Service defines Excessive Heat for southern Wisconsin when these conditions are observed: daytime heat index values of 105 or higher with minimum night heat index values of 75 or higher, for at least a 48-hour period. The National Weather Service issues Excessive Heat Warnings for those conditions. Heat-related deaths may or may not occur during Excessive Heat conditions. The National Weather Service issues Heat Advisories when daytime heat index values are expected to reach 100 to 104. Should 4 consecutive days of heat index values of 100 to 104 be expected, then an Excessive Heat Warning may be issued. History has proven that long durations of heat can adversely affect the general population. A 6 to 7-day heat wave in mid-june, 1995, in which daytime heat index values of 98 to 104 were observed across Wisconsin, there were at least 9 heatrelated deaths (National Weather Service). Heat Index The National Weather Service uses the Heat Index as an estimate of how it really feels when the effect of relative humidity is added to the actual air temperature. The National Weather Service (for the Great Lakes Region, including Dane County) issues Heat Advisories when heat index values are expected to reach 100 to 104 during the daylight hours (for one day or more), or 99 to 99 for four consecutive days. An Excessive Heat Warning is issued when heat index values are expected to reach 105 or higher during the daylight hours and Dane County 4.110

111 remain at or higher than 75 at night, for a 48-hour period, or if values of 100 to 104 during the daylight hours are expected for 4 consecutive days. Table 4.26 shows heat index values for a range of temperatures and humidity. Geographic Extent Excessive heat is a regional phenomenon often covering large swaths of the United States, and not isolated to counties or states. Figure 4.27 demonstrates the number of heat wave events for the state of Wisconsin from 1982 through 2008, displayed by county. While all counties have documented heat wave events, the number of occurrences increases in the southern and western portions of the state. Heat may be most pronounced in urban areas due to the urban heat island effect. Note the high number of heat related deaths in the Milwaukee area. However, the Milwaukee Health Department noted that other social and economic factors were partially the reason for higher number of heat-related fatalities in Milwaukee. The associated geographic extent rating is extensive, with the most pronounced affects in the central, urbanized areas of Dane County in the vicinity of Madison. Table 4.28 Heat Index Table Relative Humidity (%) Temp o F With Prolonged Exposure and/or Physical Activity: Extreme Danger: Heat Stroke or Sunstroke likely Extreme Caution: Sunstroke, muscle cramps, and/or heat exhaustion possible Danger: Sunstroke, muscle cramps, and/or heat exhaustion likely Caution: Fatigue possible Source: National Weather Service Website. Dane County 4.111

112 Previous Occurrences The data available on extreme heat is very limited. A search of data held by the Wisconsin State Climatology Office (SCO) provided observed maximum and minimum temperatures in Madison for every day from January 1, 1971 to December 31, 2008 This data, however, does not indicate heat index, nor does it provide any information regarding the impact of extreme heat events. The data does provide baseline data for the recurrence interval of such events. Table 4.29 summarizes the temperature extreme data from the SCO from 1971 through 2008, showing for each month, the number of days with high temperatures above 95º Fahrenheit. On average, Madison experiences 11 days a year with temperatures above 90º Fahrenheit. Dane County 4.112

113 Figure 4.25 Heat Wave Deaths by County for Wisconsin Source: National Weather Service Dane County 4.113

114 Figure 4.26 Heat Wave Events by County for Wisconsin Source: National Weather Service Dane County 4.114

115 Table 4.29 Heat Incidents for Dane County ( ) Month/Year Number of Days with high above 95ºF Month/Year Number of Days with high above 95ºF July August July July June (2 days above 100) July (2 days above 100) June August (2 days above 100) July June July June Sept July (1 day above 100) June August July July August July June July July August Source Wisconsin State Climatology Office Website In more recent years, the National Weather Service and the National Climatic Data Center (NCDC) have been tracking weather extremes and their consequences in greater detail. A search of the NCDC website provided the following descriptions of several excessive heat events, including the most recently documented event in 2006: June, July 1995 Dane County experienced two periods of prolonged heat in the summer of From June 17-27, high temperatures were consistently into the 90ºs F with heat index values ranging from 88º F to 104º F. During this period, statewide, 9 people died as a direct result of the heat. The second heat wave, July 12-15, resulted in the greatest number of weather related deaths in Wisconsin history. During this heat wave, 141 people died directly or indirectly from the heat, but no deaths were reported in Dane County. High temperatures were well into the 100ºs, with heat index values of 120º to 130º F. July 1999 A heat wave over the last two weeks of July, peaking on July 28-31, 1999 pushed local utility companies to the limit. There were no outages in the Dane County area, but there were records set for peak electrical demand. During these four days, high humidity and high temperatures well into the 90ºs produced heat index values to over 110º F. Statewide, the heat was directly responsible for killing 8 people and indirectly responsible for another 6. Dane County had 1 heat-related death. July 2001 Southern Wisconsin was affected by a heat wave at the end of July Afternoon heat index values on the 31st reach 110º F for several hours and stayed in the 85º F to 100º F Dane County 4.115

116 range through the evening hours. Local utilities again reported new daily record peak demands for electricity. Statewide 15 died because of heat. October 2003 A 6-month old female died in the city of Middleton. Heat was listed as a contributing cause, thus this death is indirectly related to excessive heat. Maximum temperatures in the Middleton area on October 7th and 8th were around 79º F, about 15 degrees above normal. July and August 2006 A period of very hot and humid weather began on the evening of July 30th and continued into August 2nd. Overnight temperatures only fell to 70 to 75 on the 30th, and soared into the 95 to 100 degree range during the afternoon of July 31st. With dew points in the low to mid-70s, heat index values only dropped to about 75 overnight on July 30th, and peaked in the 105 to 110 degree range across south-central and southeast Wisconsin during the afternoon of July 31st. An estimated 40 people in Milwaukee County were hospitalized due to heat-related symptoms. Ultimately, this stretch of "heat advisory" conditions resulted in two directly-related heat deaths in Milwaukee County where the urban heat-island effect is enhanced. Air temperatures only fell into the mid 70s across south-central Wisconsin and lower 80s in the Milwaukee Metro area during the early-morning of August 1st. Afternoon air temperatures soared into the 95 to 100 degree range. With dew points in the low to mid- 70s, heat index values only dropped into the lower 80s during the morning of the 1st, and peaked in the 105 to 110 degree range across south-central and southeast Wisconsin during the afternoon of August 1st. The oppressive conditions continued during the overnight hours of August 1st with low temperatures around 80 degrees before a cold front swept through during the afternoon, ending the heat wave. On August 2nd, a 67-year-old male died due to high temperatures in his West Allis (Milwaukee Co) residence. Likewise on August 2nd, a 41-year-old male died in his residence due to elevated levels of heat. Probability of Future Occurrences Excessive heat events occur about once every other year in Dane County. Though Dane County does not have the highest incidence of heat wave periods, it is located in southern Wisconsin, which is the most area most severely impacted by heat wave events. According to the National Weather Service data shown in Figure 4.26 Dane County has experienced 13 heat wave events in the 27 years between 1982 and It is extremely likely that heat waves will continue in the future. Using the formula established in Section Profile Methodology, the assessment reflects (13 events over [divide by] 27 years) x 100 = 48 percent chance of occurrence any given year, or happens on average every 2 years. This equates to a likely occurrence rating. Impact Assessment Direct Impacts The most significant direct impacts of excessive heat are to human health. Some medical conditions, for example, are considered direct impacts of excessive heat. These include dehydration and heat stroke. Adverse health outcomes associated with extreme temperatures include heatstroke, heat exhaustion, dehydration, heat syncope, and heat cramps. Heatstroke is the most serious of these conditions and is characterized by rapid progression of lethargy, confusion, and unconsciousness. It is often fatal despite medical care directed at lowering body temperature. Heat exhaustion is a milder syndrome that Dane County 4.116

117 occurs following sustained exposure to hot temperatures and results from dehydration and electrolyte imbalance; manifestations include dizziness, weakness, or fatigue, and treatment is supportive. Heat syncope and heat cramps usually are related to physical exertion during hot weather. Property impacts from excessive heat are generally minimal. Indirect Impacts Indirect impacts examine those costs which are associated with, but not directly caused by, excessive heat. The most common indirect impact of excessive heat is the loss of electricity caused by the overly-high demand for power. This indirect impact from excessive heat increases population vulnerability, as refuge from the excessive heat becomes compromised, and increases the economic impacts associated with power outages. Since very little data is collected on these indirect impacts it is difficult to make a statistical estimation of severity. Impact Magnitude and Severity Summary Figure 4.25 indicates that Dane County has one documented death caused by excessive heat since Specific injury reports are unavailable, but hospital records from indicate that over 200 patients were treated for heat-related injury and illness. According to the National Weather Service, heat waves have been responsible for more deaths in Wisconsin than all other natural disasters combined. For the period , at least 116 people have died in Wisconsin where heat was the direct or primary cause. For the same period of time, at least 95 people in Wisconsin have died when heat was an indirect or secondary cause. Property damage is equally difficult to quantify, as excessive heat does not directly impact property. Based on the known extent of property damage and injury/fatality ratings, the magnitude/severity rating for excessive heat is low. Vulnerability Assessment Population Everyone is vulnerable to excessive heat conditions, although some populations are more vulnerable than others. Excessive heat poses the greatest danger to outdoor laborers, such as highway crews and fire crews. The elderly, children, and people in poor physical health are also vulnerable to exposure to extreme temperatures, as are the homeless. Mortality among elderly persons, persons with chronic conditions (including obesity), patients taking medications that predispose them to heatstroke (e.g., neuroleptics or anticholinergics), and persons confined to bed or who otherwise are unable to care for themselves are at greatest risk. Low-income individuals and families are also at greater risk of heat exposure than the general population. According to FEMA, People living in urban areas may be at greater risk from the effects of a prolonged heat wave than people living in rural regions. Asphalt and concrete retain heat longer and gradually release heat at night, which produces significantly higher nighttime temperatures in urban areas known as the urban heat island effect. Available hospital records from indicate that no resident of Dane County has died directly from heat exposure. However, there have been over 308 visits by patients Dane County 4.117

118 during this time for various reasons, heat stroke being the most common. Some of the patients were repeat visitors. This equates to about 50 people a year. As a percentage of the total population, the population with the greatest risk for heat-related health effects is over age 65. In addition, Figure 4.25 indicates that since 1982 there has been one reported death directly associated with excessive heat in Dane County. There are also segments of the population that are vulnerable to the potential indirect impacts of prolonged excessive heat, particularly the loss of electrical power. As a group, the elderly or disabled, especially those with home health care services relying on rely heavily on an uninterrupted source of electricity. Resident populations in nursing homes, Community Based Residential Facilities, or other special needs housing may also be vulnerable if electrical outages are prolonged. If they do not have a back-up power source, rural residents and agricultural operations reliant on electricity for heating, cooling, and water supplies are also especially vulnerable to power outages. Overall, the population has a medium exposure to excessive heat events. General Property Generally, property is not considered particularly vulnerable to excessive heat. Energyinefficient buildings may be warmer, resulting in a higher exposure of the population, and personal landscaping and property may suffer from the effects of heat in a manner similar to drought. Cars may overheat, stranding motorists or damaging the vehicle itself and resulting in higher property damage costs. The overall vulnerability of general property is low. Essential Infrastructure, Facilities, and Other Important Community Assets Heat extremes present minimal direct risk to structures and critical facilities of Dane County. Critical facilities may be vulnerable to the indirect impact of prolonged excessive heat, i.e., electrical power outages, which may impact response capabilities or care capabilities for hospitals and clinics. Hospitals and clinics may see a surge in patients during the heat event as the exposed population suffers from the effects of the heat, but it is not anticipated that these increases will overwhelm the capacities of hospitals and clinics in Dane. The primary stresses to essential infrastructure are on the electrical distribution system as demand increases to run air conditioning. Peak demand exceeding the local utility s capacity for supply can lead to blackout or brownout conditions. This has not occurred in Dane County however, utilities were very closely monitoring the situation during the heat waves of 1999 and The utilities supplying Dane County have worked closely with emergency response agencies and human services providers to develop plans for responding to planned and unplanned power outages in the County. The Dane County Electrical Power Disruption Plan was developed to address this issue. The overall exposure of essential infrastructure is medium. Natural, Historic and Cultural Resources Natural resources may suffer from prolonged exposures to excessive heat, such as the drying of grasses and trees, evaporation from water sources, and an increased likelihood of wildfires. Historic resources likely experience the same vulnerabilities addressed in General Property. Cultural resources themselves are likely minimally impacted by the excessive heat; however the people using those resources may experience a higher vulnerability due to exposure. Playgrounds, for example, may be too hot for safe utilization by children. Dane County 4.118

119 Community centers and other resources providing free or low-cost air conditioning may see a drastic increase in attendance, which may stress capacity or use. All of these vulnerabilities are considered minimal. The overall exposure of these resources to excessive heat is medium. Estimating Potential Losses and Development Trends Assessment Potential Loss Estimates As can be seen from the past history data, excessive heat events are a near annual occurrence in Dane County. The costs and losses from past extreme heat events, however, are not systematically collected and compiled. There is no available data on which to base a projection of the future loss potential, which was recognized in the previous planning process. No new data collection exists to estimate financial damages due to heat. One death was reported in the last 27 years, or a 3.7 percent chance of a single death due to excessive heat in a given year. This is not anticipated to change despite population growth. Development Trends Development itself is not vulnerable to excessive heat. Newer construction may actually decrease the vulnerability of the population it shelters to excessive heat, as newer materials and construction techniques may increase the cooling effectiveness of residential or commercial facilities. Population data indicates that the overall population of Dane is expected to continue increasing. Overall Risk Summary As with severe cold, the most vulnerable aspect of Dane County to excessive heat is the population. Property may experience slight damage as vehicles overheat; contents of garages are damaged due to heat exposure, or natural landscaping experiences impacts similar to drought. Excessive heat increases the risk of wildfire, impacting natural resources. Essential infrastructure is generally not impacted by excessive heat, though clinics may see an increased demand for services as the population is exposed to the heat. Due to the population exposure, and potential fatal impacts, the overall risk rating for excessive heat is medium. The ability to quantify these assessments is not currently available, as no accurate financial data for damages incurred exists. Table 4.30 provides the methodology for how all aspects of the hazard profile were evaluated to establish an overall hazard rating. Table 4.30 Overall Risk for Excessive heat Measurement Rating Value Geographic Extent Extensive 4 Probability of Future Occurrence Likely 3 Vulnerability Assessment Medium 2 Impact, Magnitude and Severity Low 1 Overall Risk Rating Medium 2.5 Dane County 4.119

120 Severe Winter Storm Description Winter storms occur when below freezing air on the ground and in clouds combine with moisture. Moisture is needed to form clouds and cause precipitation. A storm front lifts the moist air to form the clouds. Storms that affect Wisconsin develop over southeast Colorado, northwest Canada, and over the southern plains. These storms move toward the Midwest and use both the southward plunge of cold air from Canada and the northward flow of moisture from the Gulf of Mexico to produce heavy snow over the region. Alberta Clippers, which develop in the lee of the Canadian Rockies and move southeast toward Wisconsin, not only produce accumulating snow, but can also bring strong winds and extremely cold air to the state. Winter storms are defined here by the following events: heavy intense snow showers accompanied by winds less than 35 mph that result in snow accumulations of 6 inches or more within 12 hours or less, freezing rain (which occurs when rain falls onto and freezes on cold surfaces) that results in ice accumulations of 1/4 inch or more within 12 hours or less, and blizzards which consist of sustained or frequent gusts of 35 mph or more accompanied by snow and/or blowing snow that reduces visibilities to 1/4 mile or less for 3 hours or more. Geographic Extent Winter weather is a regional event that occurs across the entire county or sometimes the entire state. Snowfall can occur anytime between October and May. More substantial winter storms occur during the winter months, most frequently between December and February. January has the most documented occurrences of severe winter weather. Between 1980 and 2008, 87 winter storms passed through Dane County and 90 percent of those storms are considered heavy snow events. Ice storms are second most common, followed by blizzards. January is the snowiest month averaging 12.9 inches with a record snowfall of 31.8 inches. December is the second snowiest month averaging 12.6 inches of snow with a monthly record of 40.4 inches. The winter of was one of the most severe on record, with over 100 inches of snowfall recorded in Dane County. Severe winter weather has an extensive geographic rating. Previous Occurrences The history of past winter storm events was gathered from NCDC data, newspaper reports and other data sources as cited. Winter storms have caused problems for Dane County residents for as long as the area has been settled. Every winter provides some challenges to the population. Some of the most recent outstanding events are listed below. March 1976 During March 4-11, a storm of freezing rain, snow, ice and wind combined into a severe ice storm that made its way across the southern portion of the state causing $50.4 million in damages statewide, at the time the most expensive natural disaster in Wisconsin history. This estimate is considered to be conservative. Unable to milk or water the cows, farming communities sustained the greatest losses. Farmers lost $17.3 million. Government damages were approximated at $8.4 million, private homes and businesses $11 million to, and utilities $13.7 million. Dane County 4.120

121 Of the 22 counties affected from the Mississippi River to Lake Michigan, Dane County was among the hardest hit. Approximately 10,000 residents lost electrical power, some for as long as 11 days. The City of Madison suffered a temporary water shortage as most of the City s water pumping stations went without power. Without heat, light, or water, many people stayed in emergency sleeping quarters prepared by the Red Cross. Dane County damages for public, farm, and private/non-farm losses, in 1976 dollars, totaled $1.9 million, $1.8 million, and $1.0 million respectively. Total damages were estimated to be $4.78 million, excluding electric utility losses, which were $1.2 million for Madison Gas and Electric, and an undisclosed amount for Wisconsin Power and Light. March 8, 1998 Near blizzard conditions brought parts of south-central and southeast Wisconsin to a standstill. The combination of heavy, wet snow, and northeast winds gusting to 40 to 50 mph, reduced visibilities occasionally to below 1/4 mile and created drifts of 8 to 15 feet in areas west and southwest of Madison. Based on newspaper accounts, there were approximately 800 motor vehicle accidents, dozens of toppled power lines, many school closings, and many road closures. Interstate 90/94 and State Highway 51 north of Madison were closed at the height of the storm. In addition, many airline flights and other commercial activities were postponed or cancelled. December 2000 December 2000 was one of the 10 coldest Decembers on record for most of the state. In addition to the low temperatures, record or near record snow depths of occurred in much of southern Wisconsin during December. As a result of record snowfalls, thirteen counties received a Presidential Emergency Declaration and were eligible to receive federal funds for extraordinary expenses associated with clearing roads and emergency response efforts. The counties declared in the snow emergency were Columbia, Dane, Door, Green, Kenosha, Kewaunee, Manitowoc, Milwaukee, Racine, Rock, Sheboygan, Walworth and Waukesha Counties. Local governments in Dane County received a total of $586,000 in federal disaster assistance. January 30, 2008 A powerful winter storm raked south-central and southeast Wisconsin during the afternoon hours of January 29th into the pre-dawn hours of January 30th. The precipitation started off as rain and thunderstorms then changed to sleet and freezing rain which then changed to snow and blowing snow with plunging temperatures. Peak sustained northwest winds were on the order of 22 to 28 knots (25 to 32 mph) with peak gusts of 34 to 43 knots (39 to 49 mph). Visibilities were occasionally reduced to 1/4 to 1/2 mile in open areas. Dozens of vehicle accidents and slide-offs were noted by the media due to very slippery roads. Afternoon temperatures in the mid 30s to lower 40s quickly dropped through the 20s into the teens and then into the single digits by the evening hours and eventually down to the - 4F to -11F by the pre-dawn hours of the 30th. Although new snow amounts were only 1 to 3 inches, County Emergency Management staff noted that this event was perceived as a winter storm due to the combination of thunderstorms, freezing rain, sleet, snow, blowing snow, strong winds, poor visibilities, and fast-falling temperatures. Synoptically, a strong low pressure moved northeast through Minnesota while a strong cold front swept southeast through Wisconsin. Another low pressure developed along the cold front while it was over northern Illinois, which led to a tightening pressure gradient and stronger winds over southern Wisconsin. Dane County 4.121

122 February 5-7, A severe winter storm spanning several days caused a traffic jam and accident involving over 1,000 cars and trucks on the northbound/westbound lanes of I-39/90. Though no injuries or deaths were reported, the damage was considerable. The Governor called a State of Emergency on the interstate and requested assistance from State Troopers from Madison and other jurisdictions within Dane county, and as far out as Wausau, Tomah, and Waukesha, Wisconsin Department of Natural Resources game wardens with snowmobiles, and wreckers were called from all over to try to get cars off the road. A number of graders from highway department were required to clear the roads. 68 soldiers from the National Guard were also called in to assist. Water and food were provided to some victims by troopers and game wardens on snowmobiles. 17 miles of I-39/90 were closed for two days. 78 schools and districts were closed or opened late. Probability of Future Occurrences Severe winter storms have been documented since settlement in the region began. Severe incidents are documented more than once yearly, with extraordinarily severe events falling approximately every other year. Using the formula established in Section Profile Methodology, the assessment reflects (58 events over [divide by] 15 years) x 100 = 100 percent chance of occurrence, which corresponds to a highly likely occurrence rating. Impact Assessment The occurrence of major snowstorms, ice storms, and blizzards can have a considerable impact on communities, utilities and transportation systems. Ice storms often produce extensive damage over large regions. The impacts of an ice storm are amplified when frigid temperatures follow the storm. Snow and ice accumulates on roads, highways, railroads, and airport runways and halts transportation efforts. Ice can cause telephone and power lines and tree branches to break and fall, which may damage property, cause injury, and create hazardous conditions. Power outages may last for days, and in some cases, it may be weeks before power is restored to more remote rural areas. As people have become increasingly dependent on electricity for heating and cooking, the possibility of experiencing a loss of electricity for an extended period has become more critical. While some of the direct impacts of ice or heavy snowstorms are easily identified, these can produce a wide range of indirect impacts. Many of these are summarized below. Direct Impacts Ice or heavy accumulations of snow, particularly with blowing and drifting, temporarily impact the roadway system. Roads can become impassable with heavy icing or as snow accumulates faster than it can be cleared. Snow and ice resulting in icy road conditions lead to major traffic accidents and numerous minor accidents. Similarly, if roads and streets are icy or snow covered, it is also difficult for emergency service personnel to travel and may pose a secondary threat to life safety if police, fire, and EMS crews cannot respond to calls. Ice or heavy accumulations of snow also require vast amounts of overtime for County and local highway and streets departments to remove snow and melt ice. Additionally, a hypothermia situation may arise due to prolonged exposure to the cold when a person attempts to walk during the height of a major winter storm. 40 Dane County Local Hazard Mitigation Plan Data Collection Guide, Dane County 4.122

123 Heavy accumulations of snow on rooftops can cause roofs to collapse, resulting in possible injury or death to those inside the building as well as damaging the contents of the building. Ice storms or high winds in winter storms can cause extensive loss of overhead utility lines due to buildup either on the lines or on adjacent trees that either collapse due to the weight or blow down onto the utility lines. Services such as telephone, electricity, and cable TV are frequently affected by winter storms. Indirect Impacts The indirect impacts are what separate an ordinary winter snowstorm, even a heavy snow, from a disaster. Heavy accumulations of snow or ice can bring down trees, utility lines, and communications towers. This can disrupt communications and electrical power for days while utility companies repair the damage. Loss of power, in conjunction with impassible roads can isolate people in rural areas and essentially shut down urban areas, effectively paralyzing the entire region. Also, many of the deaths that occur are indirectly related to the storm itself. Many of these results are from traffic accidents or heart attacks while shoveling snow. The indirect impacts of severe winter storms ripple past the actual hazard event. Economic costs incurred by loss of business as a result of the storm, property damages, overtime costs, loss of income due to closed business, and missed school days all have long-reaching effects. Increased amounts of snow may increase the risk of flooding in the summer. Other examples of indirect impacts include: Agricultural losses. Livestock, particularly dairy cattle can be highly vulnerable to the impacts of an ice storm, especially if freezing conditions exist for a long time and are accompanied by an extensive power outage. Daily operations are dependent on electricity for milking and watering the animals. Loss of revenue or even disease and death of the animals can result. Home Health Care Services. Recipients of home health care services, particularly in rural areas face disruption of services in the aftermath of an ice or heavy snowstorm. Providers may have difficulty in reaching patients due to debris or downed power lines blocking roadways. Electrically powered life support equipment will fail to operate in a power outage. This can have dire consequences to the patient if the outage is prolonged. Communications. Telecommunications can be disrupted due to a variety of factors. Most telephone and cellular carriers have emergency back-up power supplies for primary equipment. In many cases, the back-up power supply is designed to provide power for 48-hours or less. In the prolonged power outages possible with a major ice storm, this equipment will fail when the fuel for the generator runs out or the back-up batteries become discharged. Overhead telephone lines are also susceptible to the same problems as overhead electrical lines. The consequences of communications failure can be far reaching. Coordination of the public safety response to the event relies heavily on the ability to communicate. The response is invariably hampered when these systems fail. Public water supply and wastewater treatment. Water supply pumps and wastewater lift stations are vulnerable to prolonged loss of power. Many of these have back-up power supply for short-term power outages. An ice storm, however, has the potential to cause power outages that may last for days. Severely damaged trees. Ice or exceedingly heavy snow can cause substantial damage to trees in urban and rural areas. Damaged or fallen trees in urban areas block roads and sidewalks and can take down power lines. Downed or fallen trees in rural Dane County 4.123

124 areas can lead to fire hazards in subsequent years as dead trees add to the fuel load. In either case, removal of downed trees and branches can be a significant problem and cost. Residential impacts. Loss of power for residential use can lead to a loss of household heating, freezing and bursting water pipes leading to loss of fresh water supply and flooded basements, sewage back-up, and the loss of the ability to cook food. Provisions. As is common in many disasters, supplies of flashlights, batteries, shovels, bottled water, fuel, and food supplies may be short in areas immediately affected by the storm. This creates a particular stress on low-income individuals and families that are not able to stock-up on these supplies, and may cause a panic on certain supplies as stock levels drop. Economic loss. Dane County residents rely heavily on roadways and automobiles to commute to and from work. When employees cannot get to their jobs, commerce can be affected, especially if the situation lasts for days. In addition, all of the primary and indirect impacts of a major snow or ice storm can have cascading economic consequences. Impact Magnitude and Severity Summary There are no documented fatalities directly caused by severe winter weather in Dane County, but traffic records (discussed in greater detail in the vulnerability assessment) indicate that winter conditions caused approximately 1,723 accidents in Dane County in 2007, with approximately 10 resulting in at least one fatality. Four winter storm events merited Presidential Disaster declarations for the state in 1976, 1978, 2001 and most recently in These factors and the extensive indirect impacts of winter storms all combine for a magnitude/severity rating of critical. Vulnerability Assessment Population While virtually all aspects of the population are vulnerable to severe winter weather, there are segments of the population that are more vulnerable to the potential indirect impacts of a severe winter storm than others, particularly the loss of electrical power. As a group, the elderly or disabled, especially those with home health care services that rely heavily on an uninterrupted source of electricity. Resident populations in nursing homes, Community Based Residential Facilities, or other special needs housing may also be vulnerable if electrical outages are prolonged. If they do not have a back-up power source, rural residents and agricultural operations reliant on electricity for heating and water supplies are also especially vulnerable to power outages. Severe winter weather also increases the vulnerability of the commuting population. Traffic accidents occurring in winter conditions (snow, blowing snow/sand/dirt, and sleet/hail) accounted for 13,518 accidents in Wisconsin in of these resulted in at least one fatality, for a rate of 0.3 percent. Icy and snowy roads accounted for 20,756 accidents in the State, 63 of which were fatal at a rate of 0.3 percent. These accidents, combined, accounted for over 21,000 accidents, or 16.8 percent of all accidents in the state. Dane County experienced 10,255 total accidents in 2007, so assuming the corresponding percentage; winter storms caused 1,723 accidents in Dane County in 2007, with Dane County 4.124

125 approximately 10 of these accidents resulting in a fatal accident. 41 While there is no way to quantify which of these accidents occur during severe winter storms versus regular winter storms, the numbers indicate that winter driving conditions raise the vulnerability of the commuting population. Overall, the population vulnerability to severe winter storms is medium. General Property Property vulnerabilities to severe weather include damage caused by high winds, ice, or snow pack and subsequently melting snow. Vehicles may be damaged by the same factors, or temporarily un-useable due to the driving conditions created by severe winter weather. Contents of homes, storage units, warehouses and storefronts may be damaged if the structures are compromised or fail due to the weather, or during potential flooding caused by melting snow. Very wet snow packs down densely and is very heavy. This may create strains on structures, causing partial or entire collapses of walls, roofs, or windows. This is impacted both by architecture and construction material, and should be assessed on a building-by-building basis. These records are probably tracked via insurance or other private vendors. The overall vulnerability rating of general property is considered medium. Essential Infrastructure, Facilities, and Other Important Community Assets The physical structures which comprise essential infrastructure are as vulnerable as those outlined in the General Property subsection of this profile. Severe winter weather may also disrupt the availability of services from essential infrastructure, including utility delivery (gas, electric and water), telephone service, emergency response personnel capabilities, road plowing, and childcare availability. Severe winter storms may even halt the operation of the county for periods of time, making the vulnerability of the entire County even higher. As mentioned previously, ice or heavy accumulations of snow, particularly with blowing and drifting, can temporarily impact the roadway system. These accumulations also require vast amounts of overtime for County and local highway and streets departments to remove snow and melt ice. Ice storms or high winds in winter storms can cause extensive loss of overhead utility lines due to buildup either on the lines or on adjacent trees that either collapse due to the weight or blow down onto the utility lines. Services such as telephone, electricity, and cable TV are frequently affected by winter storms. The overall vulnerability of essential infrastructure is medium. Natural, Historic and Cultural Resources Natural resources may be damaged by the severe winter weather, including broken trees and death of unsheltered wildlife. Unseasonable storms may damage or kill plant and wildlife, which may impact natural food chains until the next growing season. Historical areas may be more vulnerable to severe winter storms due to construction and age of structures. Cultural resources generally experience the same vulnerabilities outlined in General Property, in addition to lost revenue impacts due to transportation impacts. The overall vulnerability of these resources is medium. 41 Wisconsin Department of Transportation 2007 Wisconsin Traffic Crash Facts: Section 2, Crashes. Available online at last accessed March 3, Dane County 4.125

126 Estimating Potential Losses and Development Trends Assessment Potential Loss Estimates The potential for future damages is estimated by assuming similar impacts as those caused by the 1976 ice storm. Public, farm, and private/non-farm losses were $5.8 million, $5.5 million, and $3.3 million respectively. Total damages are estimated to be $14.5 million, excluding electric utility losses, which were $3.6 million for Madison Gas and Electric, and an undisclosed amount for Wisconsin Power and Light (now Alliant Energy). Snow removal costs were approximately $3.6 million. Overall, this totals to $ million in 2008 dollars. Like fog, winter storms are dangerous hazards on Dane County roadways. Between 1998 and 2002, 604 people were injured and 9 were killed when snow was present on the road and precipitating. That averages to 151 injuries and about 2 deaths per year. Development Trends As the County continues to develop, a greater number of structures, roadways, and population are exposed to severe winter storms. More roads will increase the need for snowplows and other means of keeping travel ways clear. Denser populations increase the number of expected injuries and deaths attributed to severe winter storms, but do not reflect an overall increase in the mortality of the disaster itself. Structures built to modern building codes may decrease the amount of general property damage due to heavy snowfalls. Because of growth the current capabilities of emergency response personnel can be taxed or overwhelmed during an event, which compromises the quality of provided services during said events. Potential for future damages could to increase for utilities. Agricultural losses may decrease as the number of cattle and dairies decreases in the County. Injuries to vulnerable populations may increase as those populations increase. Overall Risk Summary Overall, severe winter storms present a high risk for Dane County. The events occur frequently and over significant portions of the county, maximizing the potential to impact exposed population and structures, and have far reaching indirect impacts. Reports of damage to property and the impacts on essential infrastructure are high. Table 4.31 provides the methodology for how all aspects of the hazard profile were evaluated to establish an overall hazard rating. Table 4.31 Overall Risk for Severe Winter Storm Measurement Rating Value Geographic Extent Extensive 4 Probability of Future Occurrence Highly Likely 4 Vulnerability Assessment Medium 2 Impact Magnitude and Severity Critical 3 Overall Risk Rating High 3.25 Dane County 4.126

127 Tornado Description A tornado is a violently rotating column of air (vortex), extending from the base of a convective cloud (usually cumulonimbus) to the ground. There may or may not be a visible condensation funnel (what most people refer to as the funnel cloud) associated with the tornado. Therefore, a tornado may be nearly invisible since one can not see vortex of rotating air. Literally, in order for a vortex to be classified as a tornado, it must be in contact with the ground and the cloud base. 42 Tornadoes usually form under certain types of atmospheric conditions. They are more likely to occur in regions where there are strong contrasts in temperature and humidity across short distances. Nationally, these conditions are most common in the central plains of North America, east of the Rocky Mountains and west of the Appalachian Mountains. They occur mostly during the spring and summer, starting earlier in the south and later in the north. According to A Tornado Climatology of Wisconsin, the typical day with tornadoes usually begins with warm and humid conditions with a few fair-weather cumulus clouds developing vertically over time in the unstable air. Later the first sign of an approaching thunderstorm is observed a high thin layer of ice clouds called cirrus blowing off the tops of the thunderstorm to the west. 43 Rotation in a thunderstorm begins when air entering the storm near the surface is blowing from different direction than air higher in the atmosphere. The rotation usually starts as a roll or horizontal rotation of the air in the lower 10,000 feet of the atmosphere. The warm updraft feeding the storm develops further, lifting one end of the rolling air and transforms the rotating mass into a vertical position. Most tornadoes rotate counterclockwise (cyclonically) in North America. Tornadoes may last for anywhere from a few minutes to up to an hour. The width of a tornado may range from a few yards to over a mile; the path of a tornado may range from a few hundred yards to hundreds of miles. 44 Through observational studies, T. Theodore Fujita created the Fujita Scale (commonly known as the F Scale ) in 1971 to classify tornadoes based on damage caused by the tornado in correlation to wind speed. However, over the years this scale has revealed several weaknesses and in 1992, Fujita published his memoirs called Mystery of Severe Storms which included an updated scale. This updated scale maintained the original classification of tornado wind speeds with damage assessments based on the type of structure. These improvements were incorporated by a committee convened by Texas Tech University (TTU) Wind Science and Engineering (WISE) Research Center to design the Enhanced Fujita Scale, commonly known as the EF Scale. One of the most important factors of the EF Scale is that it includes previous F Scale ratings to create consistency between the initial tornado databases, which stretch back into the 1950s, and the more contemporary measurement systems. This new system still uses wind estimates (not measurements) based on damage to assign scale ratings. It uses three-second gusts estimated at the point of damage based on a judgment of 8 levels of damage to one of 28 indicators (building types and materials). The estimates also vary with height and exposure. A table depicting these damage indicators and specific information can be found 42 American Meteorological Society, Glossary of Meteorology 2nd Edition. Available online at last accessed on February 11, National Severe Storms Laboratory FAQ About Tornados. Available online at last accessed on February 11, Ibid. Dane County 4.127

128 on the National Weather Service website at A table showing the relationship between the original Fujita Scale and the Operational EF Scale, which was enacted as the standard measurement system in the United States beginning February 1, 2007, is presented in Table Table 4.32 Fujita and Enhance Fujita Scale F Number Fujita Scale Derived EF Scale Operational EF Scale Fastest 1/4-mile (mph) 3 Second Gust (mph) EF Number 3 Second Gust (mph) EF Number Second Gust (mph) Over 200 Source: National Weather Service. Available online at Geographic Extent Tornados are documented across Wisconsin, as demonstrated in Figure 4.27 Dane County currently has more reported tornado events than any other county in Wisconsin for the period of This is partially due to the fact that Dane County is a large county the larger the county the greater the chances that a tornado will occur within its boundaries. However, Southern Wisconsin tends to experience more tornadoes than northern Wisconsin since it is closer to the storm track that pulls warm and moist air up from the Gulf of Mexico. Warm, moist air is the fuel for thunderstorm development. Figure 4.28 shows the tornado paths or, for short-duration events, the tornado touch-down points. This figure indicates that tornados occur in any portion of the county and often cross county lines. As any portion of Dane County is vulnerable to a tornado, the associated geographic extent is extensive. Despite this overall possibility of tornados, a single tornado does not impact the entire county simultaneously and damages less than five percent of the total county area in any given event (an extreme example: a 1-mile wide tornado going northeast along the 51-mile diagonal of Dane County would damage 51 square miles, or only 4.2% of the total county area). This rates between a limited and significant extent rating, based on the size of the tornado. Averaging these two considerations together, the overall geographic extent of tornados for Dane County is significant. Previous Occurrences Between 1844 and 2008, 67 tornadoes of varying intensities have been recorded in Dane County. In fact, more tornadoes have occurred in Dane County than any other county in the State. The vast majority of tornadoes recorded had intensities classified as F0-F2. The NCDC database has recorded 48 tornados over the past 53 years. Of these, 12 events were rated as F2 tornados and four events were classified as F3 tornados. While the NCDC database has no higher records than an F3 for Dane County, Figure 4.28 indicates at least one F5 tornado occurred during this time period. Further research indicates the tornado was actually an F2 when it entered Dane County. This tornado reached F5 intensity just to the Dane County 4.128

129 west in the Barneveld area of Eastern Iowa County. Dane County has received one state disaster declaration and four presidential disaster declarations since 1971 for tornados. 45 Past tornadoes in Dane County have traveled as little as a tenth of a mile, but have gone on for as many as 36 miles. Tornadoes have passed through numerous populated areas, such as the City of Sun Prairie, Village of DeForest, Village of Black Earth, the City of Monona, the City of Stoughton, and the City of Madison 45 Wisconsin Emergency Management County Disasters Since Available online at last accessed on February 11, Dane County 4.129

130 Figure 4.27 Tornado Events in Wisconsin by County Source: National Weather Service Dane County 4.130

131 Figure 4.28 Tornado Incidents and Paths for Dane County ( ) Dane County 4.131

132 Data from the National Weather Service (NWS), indicates that more tornadoes have affected Dane County in the past five decades, as compared to previous decades. However, much of this increase is due to greater documentation efforts by NWS meteorologists, especially from the 1980s to the present. Prior to the 1960s, unless a tornado struck Main Street in broad daylight, it likely went undocumented. Additionally, severe weather spotter and research videotapes of tornadoes in the past 20 years has shown that a tornado can be in progress, but a visible funnel cloud may be absent or poorly defined. In these cases, confirmation of a tornado is based on a rotating dirt/debris spray observed at ground and cloud-base rotation directly above. 46 In more recent years, the National Weather Service and the National Climatic Data Center (NCDC) have been tracking weather extremes and their consequences in greater detail. A search of the NCDC website provided the following descriptions of several tornados from the past twenty years: June 1984 At approximately 12:41 am the 8th of June an F5 Tornado touched down in neighboring Iowa County, leveling Barneveld, a village of over 600 people. One of the few structures left standing was the water tower. The Barneveld Tornado remained on the ground throughout its entire 36-mile journey. Additionally, the path of the tornado s destruction was exceptionally wide, at times 300 yards. Soon after touching down in Barneveld, the tornado headed on a northeast path into Dane County. The path of the tornado went through the Town of Vermont and through the Village of Black Earth, and the NCDC records indicate the Tornado had dissipated to F2 intensity by that time. The records from the Town of Vermont were not available to verify this at the time of the 2009 update. Twenty-four homes were damaged and at least 8 were destroyed. Woodlots were plucked clean of foliage and branches, and some trees were uprooted from the ground. Once the tornado dispersed, nine people were left dead (all in Barneveld) and about 200 were left injured as a direct result of the storm. Total damages exceeded $66.3 million. Dane County damages totaled approximately $4.1 million. Dane County received a Presidential Disaster Declaration to assist with recovery costs from this storm. The Town of Vermont offers these thoughts in their data collection guide: Occurring in 1984, and known as the Barneveld Tornado, it skipped diagonally through the Town of Vermont. It damaged and destroyed a number of homes and farm buildings. There was considerable road blockage from fallen trees and crop destruction both from the wind and from debris in the fields. September 1992 On June 17 at 12:06 pm, an F3 tornado struck Dane County. The tornado first touched down in the Village of Belleville, about 15 miles south of the City of Madison, and began its trek northeast touching down just east of Highway 69 damaging farm structures and killing livestock. It then headed into the City of Fitchburg leveling a subdivision (18 homes total) severely damaging the Oregon Correctional Facility, destroying 20 buildings. The tornado also did damage in the Town of Dunn, destroying numerous homes. Although no deaths were reported approximately 30 people sustained injury. An estimated 201 homes were 46 National Weather Service Milwaukee-Sullivan, 2009 Dane County 4.132

133 damaged totaling $30.6 million in losses. Damages are estimated at 30 homes destroyed, 34 with heavy damage, 29 with medium damage, and more than 130 incurred minor damage. Dane County received a Presidential Disaster Declaration to assist with recovery costs from this storm. August 18, 2005 A strong and destructive tornado spun up at 1715CST about 2.8 miles southeast of the geographic center of Fitchburg (or 2.0 miles north of center of Oregon), about 400 yards southwest of the intersection of CTH MM and Schnieder Rd. It continued east-southeast to the southern edge of Lake Kegonsa and tore through residential neighborhoods about 1/3 to 1/2 mile north of the towns of Dunn and Pleasant Springs, and far-northern Stoughton. It moved with Interstate 90/39, and stayed close to CTH A to its exit point at 1905CST where CTH A crosses into Jefferson County, about 2.8 miles south-southwest of Rockdale. One person was crushed to death in their basement from fireplace and chimney bricks that crashed through the floor. Twenty-three (23) other people were directly injured. In addition, Emergency Management officials received reports of 2 other indirectly-related deaths associated with this strong tornado. In these two cases, the people were already very ill or suffering from a life-ending disease. Injuries they received during the tornado contributed (secondary) to their death, but were not the primary cause of death, based on medical examiner reports. Consequently, these additional two deaths do not appear in the official death tally in the header strip of this event. Numerous homes, businesses, farm buildings, vehicles, power-lines, trees, and other personal effects were either damaged or destroyed along its path that grew to a maximum width of about 600 yards north of Stoughton. As for residential structures, 220 sustained minor damage, 84 had major damage, and 69 were destroyed. As for business structures, 6 sustained minor damage, 1 had major damage, and 1 was destroyed. As for agricultural structures, 5 sustained minor damage, 5 had major damage, and 40 were destroyed. The overall slow movement (the supercell moved at knots, or mph), coupled with structures that were not thoroughly reinforced (based on NWS damage survey), allowed the tornado's cyclonic winds to more severely damage buildings in its path. Consequently, although some of the worst damage resembled what would be left by a F4 tornado for well-built homes, this tornado was rated at the top of the F3 category with estimated winds near 174 knots (200 mph). Total estimated damage amounts (directly-related) for private and public sectors combined was $35.06 M, broken down to $34.31 million in property damage and $750,000 in crop losses, for the tornado segment in Dane County. The $34.31million in property damage was broken down to private losses (total of $32.29 million) and public losses (total of $2.02 million), per Emergency Manager reports and NWS estimates. The private losses included a total of $25.45 million for residential structures; $1.29 million for businesses; $4.25 million for agricultural structures; $1 million for damage to vehicles, boats, and other personal effects; $200,000 to agricultural machinery and tools; and $96,000 in public road system damage. The public losses making up part of the $34.31 M consisted of $2.02 M in damage to public utility systems. The $750,000 in damage attributed to crop losses occurred on an estimated 1,550 acres of land. Additional monetary costs incurred in the public sector (totaling $1.84 million) which are considered indirectly-related damage expenses, and not included in the "direct" totals listed in the header-strip of this event, include: $1.38 million in debris clearance; $308,000 in protective measures; and miscellaneous damage/expenses of $144,000. Therefore, the grand total of direct and indirect damage amounts and expenses attributed to this tornado segment in Dane county totaled about $36.89 million. The State Disaster Fund provided relief aid for this disaster. The Stoughton Attachment has additional specifics on impacts to the City of Stoughton. Dane County 4.133

134 In addition to this tornado, a minor F0 tornado developed approximately 2 miles westsouthwest of the Village of Dane, and traveled northeast, ending 0.8 miles north of Dane. Some crop damage was reported, but the overall rating was an F0. Another tornado developed just north of the F3 Stoughton tornado bath, about 1.6 miles south-southwest of Rockdale. Many large trees were uprooted or twisted and minor damage was inflicted on three homes and one pole shed, in addition to knocking down power lines. This tornado was rated an F1 with estimated winds of knots ( mph) and the average path width was about 50 yards. This was part of the largest single-day tornado outbreak in Wisconsin recorded history for south-central and southeast Wisconsin. A total of sixteen tornadoes were documented on this day. June 7, 2008 This tornado moved from just west of Hults Road on the far western part of Stoughton northeast to a point northwest of the intersection of CTH B and CTH N. Based on the observed damage, it was probably a multiple-vortex tornado. In the Stoughton area, with respect to residential homes, it resulted in very minor damage to 24 homes, minor damage to 21 homes, and major damage to 3 homes. Additionally, 1 church sustained major damage, and 1 tobacco shed was destroyed. Total estimated property damage (roofs, siding, walls, windows) in the Stoughton area was $409,000. June 12, 2008 This tornado in south-central Dane County was a continuation of a tornado that spun up mid-way between the city of New Glarus and the village of Postville in northwest Green County. It entered Dane County on the west side of the City of Belleville and then moved northeast through the Lake Belle View area and crossed STH 69 about 1 mile north of the County Line, and ultimately dissipated southeast of Basco, near CTH A. Luckily only tree damage occurred - of the uprooted tree or broken tree branch variety. Wind speed estimated at knots ( mph). The average path width in Dane County was about 60 yards. Probability of Future Occurrences Tornados are reported in Dane County nearly every year. Using the formula established in Section Profile Methodology, the assessment reflects (49 events over [divide by] 53 years) x 100 = 92 percent chance of occurrence and a likely occurrence rating. This information is drawn from the NCDC database and was current as of February Impact Assessment The National Weather Service considers tornadoes to be among nature s most violent storms. The most violent tornadoes are capable of tremendous destruction with wind speeds of 250 mph or more. Tornadic winds can cause people and autos to become airborne, rip ordinary homes to shreds, and turn broken glass and other debris into lethal missiles. Even weaker tornados can cause large economic damages. For example, a F1 tornado in June 2008 caused $429,000 in damages, while an F3 tornado in August 1967 caused only $25,000. Though the strength of the tornado often dictates the impacts, it is important to remember that the location (rural or uban) of the tornado is just as important when assessing these risks. Dane County 4.134

135 Direct Impacts Directly, tornados impact the physical contents of the County, including structures, crops, and population. Damages caused by the tornado results in large amounts of debris, which may clog transportation networks, create a large population who require shelter or alternative living conditions, and may delay the response of emergency personnel during and after the event, and the arrival of relief supplies and assistance following the event. As with almost all disasters, there are also psychological impacts on the population both directly and indirectly affected by the event which may result in immediate or delayed reactions to the event. Indirect Impacts Indirect impacts of tornado include the often large rebuilding costs and timeframes for reconstruction or repair of damaged homes, shops, roadways, or other buildings. When a tornado event impacts a large portion of the community, these impacts may increase in severity as the timeframe of recovery is prolonged. The psychological impact of tornados may indirectly impact the community s recovery as well. Loss of revenue due to closed and damaged buildings, damaged transportation networks, and delayed employment conditions may also indirectly or directly impact the communities. Impact Magnitude and Severity Summary The damage to property, essential infrastructure and human life ranges from minimal to catastrophic based on the sporadic nature of the events. The variability of these impacts does not lessen the dangers of the events, however. Based on the worst case magnitudes and severity ratings examined in this profile, the overall rating for tornados in Dane County is catastrophic. Vulnerability Assessment Exposure is measured by the relative effect of tornados on four categories: Population, General Property, Essential Infrastructure, and Natural, Cultural or Historic Resources. Each category is analyzed to reflect the specific and general exposures to the hazard, and assigned a corresponding exposure rating ranging from low to high. The overall exposure assessments are captured by averaging the ratings for each category. For a tornado, the overall exposure assessment for Dane County is medium. Population Populations are the most vulnerable to tornados. The availability of sheltered locations such as basements, buildings constructed using tornado-resistant materials and methods, and public storm shelters, all reduce the exposure of the population. However, there are also segments of the population that are especially exposed to the indirect impacts of tornadoes, particularly the loss of electrical power. These populations include the elderly or disabled, especially those with medical needs and treatments dependant on electricity. Nursing homes, Community Based Residential Facilities, and other special needs housing facilities are also vulnerable if electrical outages are prolonged, since backup power generally operates only minimal functions for a short period of time. The Dane County capacity counts for these facilities indicate 15,827 exposed people just within documented, licensed care centers. Approximately 10 percent of the population over the age of 5 is disabled in some way, and 35 percent of the population is considered exposed due to age, either under the age of 18 or over the age of 65. These individuals may have difficulty reaching shelter in Dane County 4.135

136 time without assistance, or may be concentrated in large groups, such as day care centers, which require additional time to safely shelter all occupants. The estimated 11 percent of the population that lives below the poverty line are also exposed as they may not have access to adequate shelters. Overall, the vulnerability of the population to tornados is medium. General Property General damages are both direct (what the tornado physically destroys) and indirect, which focuses on additional costs, damages and losses attributed to secondary hazards spawned by the tornado or due to the damages caused by the tornado. Depending on size of the tornado and the length of time a property is exposed to the event, a tornado is capable of damaging and eventually destroying almost anything. Construction practices can help maximize the resistance of the structures to damage, but it is difficult to project these impacts into general vulnerability assessments because of the variability of the construction uses. Table 4.33 lists the total parcel counts and values for the property in Dane County. Property is considered to have a medium vulnerability rating to tornados. Essential Infrastructure, Facilities, and Other Important Community Assets Secondary impacts of tornado damage often result from damage to infrastructure. Downed power and communications transmission lines, coupled with disruptions to transportation, create difficulties in reporting and responding to emergencies. These indirect impacts of a tornado put tremendous strain on a community. In the immediate aftermath, the focus is on emergency services. Law enforcement activities focus on scene security. Fire and EMS personnel rescue the injured, put out any fires caused by broken gas lines or other similar hazards and assist in the clean up. Utility crews restore power, phone and other utility services. Highway and public works crews remove debris from roadways. Victims and their insurance agents need access to the properties to assess the damage and search for valuables or heirlooms. The overall vulnerability of essential infrastructure is medium. Natural, Historic and Cultural Resources Just as any property, infrastructure, or population is vulnerable to a tornado, any natural, cultural or historic resource in the path of a tornado event is impacted. Direct impacts are combination of the structural damages discussed in General Property, the exposures of the population frequenting the resource, and the additional dimension of potentially irreplaceable losses if artifacts, artwork, historical documents, and other cultural resources are destroyed. Large community resources which may serve as shelters in the aftermath of a disaster are also vulnerable, and any sustained damages or losses to them may impact the ability of the community to recuperate from the disaster. The overall vulnerability of these resources is medium. Estimating Potential Losses Potential Loss Estimates The potential for future losses due to tornado damage is estimated based on an extrapolation of losses from past events. There are limitations to this method: Every tornado is unique in location, duration, and intensity. It is impossible to predict with any degree of certainty where and when a tornado will strike. As a result, the risk of tornado occurrence is essentially uniform, countywide. Dane County 4.136

137 The exposure to damage increases as the population of the County increases. Future damages may increase simply due an increase in the amount of exposed property. This method of estimation cannot account for increasing risk due to growth. Indirect impacts are not well accounted for. The damages resulting from a tornado depend greatly on where and when the storm hits. A severe tornado tracking through an undeveloped area may cause less damage than a weak tornado striking an urban or residential area. While the estimation of future losses based on past events is unsophisticated, it still is a useful method of quantifying the damage potential. The following assumptions were made for this estimation: Based on NWS data in GIS format developed by Geographic Techniques, spanning the time period of 1955 to 2008, the average tornado in Dane County is 6.2 miles long and 104 yards wide, and remains on the ground for an average of 7.5 minutes. Average affected area by a tornado equals 540 acres. The average intensity is F2. Residential, commercial, and manufacturing and agricultural properties are evenly distributed across the County. The Fujita Scale was designed with a "well-constructed" frame house as the standard for assessing failures in building construction. Due to the variability in the quality of construction and other factors, some buildings may experience less or more damage than others when exposed to F2 category wind speeds. In addition to structural damage, building contents and personal property will also be damaged or destroyed as a result of a tornado. Approximations of the value of building contents are based on the FEMA estimates collected in Table To account for the variations in construction and the actual distribution of residential, commercial, and manufacturing properties, a range of damage potentials, as collected in Table 4.33 were used. Calculations performed using these tables are presented as an average, with sitespecific variations expected, but not easily quantified. They provide an "average expectation" or "typical impact". Table 4.33 Average Loss Expected By Fujita Damage Scale Fujita Scale Damage Description Percentage of Structure and Building Contents Value Lost due to Damage F1 F2 F3 F4 and above Moderate Damage. Roof surface peeled off; window breakage; attached garages may be destroyed. Considerable damage. Roofs torn off frame houses; light object missiles generated. Severe Damage. Roof and some walls torn off well constructed houses. Devastating Damage. Well-constructed houses leveled; structures with weak foundations blown off some distance; large missiles generated. Source: Dane County Emergency Management. 0% to 20% 50% to 100% 100% 100% In order to calculate the property damaged by the average tornado, the number of residences, commercial and manufacturing structures, and acres or crops affected by the area of the average tornado was determined for each municipality and the County. The average tornado area was divided by each municipality s area, resulting in a percent of area Dane County 4.137

138 impacted, or affected area. Multiplying the improved value plus content value of all structures by the percent affected area yields the exposure of affected property. Multiplying the affected area by the number of improved parcels yields an estimate of the number of structures impacted. Final loss ranges are calculated by multiplying the exposed property value by 50 percent for the low and 100 percent for the high, based on the average impacts in Table A low damage estimate was calculated using a value of 25 percent of the exposed property value. The expected losses from this average tornado, by jurisdiction, can be referenced in each jurisdictional annex. A summary table by jurisdiction is provided in Table 4.34, sorted by loss ratio. The loss ratio analysis was conducted on the moderate damage range. The loss ratio is the estimated loss divided by the total exposed value. The higher the ratio, the more difficult it would be for the community to recover from the event. Table 4.34 Tornado Loss Estimate by Jurisdiction Participating Municipality City of Edgerton City of Fitchburg City of Madison City of Middleton City of Monona City of Stoughton % area of jurisdiction impacted Improved Parcel Count Affected Structure Estimate Total Exposed Value ($) Estimated Loss $ (High Damage Range) Estimated Loss $ (Moderate Damage Range) Estimated Loss $ (Low Damage Range) Loss Ratio for Moderate Damage Range % ,780,700 37,780,700 18,890,350 4,722, % 2.40% 6, ,759,335,500 66,224,106 33,112,053 8,278, % 1.09% 53, ,885,068, ,953, ,976,706 31,244, % 10.06% 5, ,830,137, ,848, ,424,365 35,606, % 25.71% 2, ,184,532, ,529, ,264,676 38,066, % 16.58% 4, ,181,541, ,926,345 97,963,173 24,490, % City of Verona 13.86% 3, ,650,962, ,759, ,379,849 28,594, % Village of Belleville Village of Blue Mounds Village of Brooklyn Village of Cambridge Village of Cottage Grove Village of Cross Plains Village of Dane Village of Deerfield Village of DeForest Village of Maple Bluff Village of Marshall 53.47% ,536,250 99,736,161 49,868,080 12,467, % 96.32% ,233,200 60,907,397 30,453,699 7,613, % % ,047,150 62,047,150 31,023,575 7,755, % 66.70% ,303, ,931,419 55,465,709 13,866, % 25.90% 1, ,462, ,560,607 78,280,304 19,570, % 52.81% 1, ,624, ,831,822 89,415,911 22,353, % 73.72% ,862,150 61,823,593 30,911,796 7,727, % 39.14% ,322,050 70,969,841 35,484,921 8,871, % 11.23% 2, ,518, ,907,744 54,953,872 13,738, % % ,996, ,996, ,998,150 30,999, % 36.90% 1, ,221,250 83,479,844 41,739,922 10,434, % Dane County 4.138

139 Participating Municipality Village of McFarland Village of Mount Horeb Village of Oregon Village of Shorewood Hills Village of Waunakee Town of Albion % area of jurisdiction impacted Improved Parcel Count Affected Structure Estimate Total Exposed Value ($) Estimated Loss $ (High Damage Range) Estimated Loss $ (Moderate Damage Range) Estimated Loss $ (Low Damage Range) Loss Ratio for Moderate Damage Range 24.28% 2, ,863, ,237, ,118,569 25,029, % 26.50% 2, ,647, ,023,479 78,511,740 19,627, % 19.43% 3, ,588, ,425,977 94,212,988 23,553, % % ,176, ,176, ,588,457 50,397, % 13.52% 3, ,365,293, ,569,214 92,284,607 23,071, % 2.38% 1, ,759,700 5,090,343 2,545, , % Town of Berry 2.35% ,225,200 3,112,552 1,556, , % Town of Bristol Town of Cottage Grove 2.49% 1, ,555,850 10,507,137 5,253,569 1,313, % 2.60% 1, ,983,950 9,215,822 4,607,911 1,151, % Town of Dunn 2.98% 2, ,704,250 14,926,184 7,463,092 1,865, % Town of Madison Town of Middleton Town of Montrose Town of Oregon Town of Pleasant Springs Town of Primrose Town of Roxbury Town of Rutland Town of Springdale Town of Springfield Town of Sun Prairie Town of Vermont Town of Verona Town of Vienna 56.49% 1, ,044, ,968, ,484,302 29,871, % 5.30% 2, ,055,298,735 55,974,540 27,987,270 6,996, % 2.47% ,592,850 2,563,049 1,281, , % 2.71% 1, ,894,100 10,827,402 5,413,701 1,353, % 2.53% 1, ,400,850 11,136,695 5,568,348 1,392, % 2.36% ,708,150 1,690, , , % 2.35% ,212,650 4,308,941 2,154, , % 2.38% ,744,400 5,702,623 2,851, , % 2.39% ,520,800 6,813,359 3,406, , % 2.33% ,884,100 8,331,334 4,165,667 1,041, % 2.80% ,724,600 7,232,855 3,616, , % 2.35% ,530,800 2,719,717 1,359, , % 3.38% ,634,825 8,569,798 4,284,899 1,071, % 2.38% ,592,850 4,937,752 2,468, , % Town of 3.81% 1, ,879,150 24,618,753 12,309,377 3,077, % Dane County 4.139

140 Participating Municipality Westport Town of Windsor % area of jurisdiction impacted Improved Parcel Count Affected Structure Estimate Total Exposed Value ($) Estimated Loss $ (High Damage Range) Estimated Loss $ (Moderate Damage Range) Estimated Loss $ (Low Damage Range) Loss Ratio for Moderate Damage Range 2.95% 2, ,987,250 16,704,774 8,352,387 2,088, % Using these estimations, the damage potential range for an F2 tornado with an average track length of 6.2 miles and width of 104 yards is between $845,000 and $201 million for the moderate damage range, depending on what jurisdiction is impacted. The average of this range is $47 million. This includes only losses directly due to the tornado s destruction. Government emergency response and recovery costs and indirect impacts are not included in this figure. The event of record is the 2005 Stoughton tornado, which caused a total estimated damage amount of $36.89 million. The entire documented costs of damages in Dane County caused by tornados, between the spring of 1955 and the summer of 2008, is approximately $70 million. Assuming this total cost can be spread evenly over the 49 documented events in the NCDC database, the average cost of a tornado is $1.4 million. Losses could be much higher, depending on where the tornado occurs. Development Trends The exposure to tornados will increase as growth and development trends continue in the County. Tornado-resistant construction can lower the exposure of population, and potentially reduce property damage costs. Integrating tornado shelters/safe rooms into new development can help reduce the exposed population. The potential alteration of the landscape (such as leveling previously hilly land for development) may have an impact on the severity of tornado damage, although there is not currently scientific information to support this theory. Dane County s population is expected to age as the Baby Boomer trend continues forward, therefore increasing these potentially vulnerable populations due both to age and living conditions. Overall Risk Summary Dane County has the highest number of reported tornados in the state. Tornado damages recorded on the NCDC database from the spring of 1955 through the summer of 2008 totaled approximately $70 million, making it one of the most costly natural hazards to impact Dane County. Only Flooding (with an estimated $385 million in damage from 1996 to 2008 reported to NCDC) and Winter Storms (with an estimated $135 million in damages reported) have more catastrophic fiscal impacts in a consistently quantifiable form. Tornadic winds primarily damage structures, though crop losses have occurred. Since the mid-1800s, only four people have died from tornadoes in Dane County, but 66 have sustained injury. Based on these past impacts, and the potential for future tornado losses and loss of life, the overall risk rating is considered high. Table 4.35 provides the summary of all aspects of the hazard profile that were evaluated to establish an overall hazard rating. Dane County 4.140

141 Table 4.35 Overall Risk for Tornados Measurement Rating Value Geographic Extent Significant 3.0 Probability of Future Occurrence Likely 3.0 Exposure Assessment Medium 3.0 Impact Magnitude and Severity Catastrophic 4.0 Overall Risk Rating High Wildfire Description Wildfire is any free burning and (at one time) out of control forest fire, grassland fire, rangeland fire, or urban-interface fire which consumes the natural fuels and spreads in response to its environment. While often considered as a destructive force, wildfires also play a positive role in nature by clearing underbrush, controlling insect populations, and depositing nutrients into the soil. Many plant species have evolved to cope with and take advantage of wildfires. Periodic, spatially-interrupted burn patterns lead to higher species diversity and healthier ecosystems. Unfortunately, when wildfires ignite in altered ecosystems (such as housing developments), the intensity, duration, and spread of the fire also change. Wildfire becomes a destructive force for ecosystems, resulting in heightened erosion conditions and other damages to the environment, in addition to the property damages sustained by human developments. Certain conditions must be present for wild fires to take hold. The most common conditions include: Hot, dry, and windy weather; Inability of the fire service to contain or suppress the fire; Occurrence of multiple fires that overwhelm local resources; and Large fuel load. Once a fire has started, additional conditions will influence its behavior, including topography and land-use patterns. The vast majority of wildfires in Dane County are human-caused. Wildfires initiated by lightning are very rare. When wildfires do occur in Dane County it is also very rare that a home or business is lost. Wildfires are most common in the spring when brush is still brown and dry. Geographic Extent Historically, the County contained fire-maintained plant communities such as prairies, oak savannas, oak or pine barrens, and oak woodlands. Fire occurrences ranged from annually to about once a decade. North facing slopes and areas with natural firebreaks (north and east of lakes and rivers) burned less frequently. The fires were frequent and burned lightly enough in the oak areas to prevent the death of mature, thick-barked trees. The jack pine areas usually experienced more severe, stand-killing crown fires which occurred less frequently than the oak and prairie fires. Current natural fire patterns are altered though Dane County 4.141

142 deliberate fire suppression actions and the introduction of fuel breaks such as roads, developed areas and agricultural fields. Most of the County is managed under a cooperative fire management program overseen by individual fire districts. The northwestern portion of the County is under state jurisdiction and classified as an extensive fire area, and includes the jurisdictions of the Towns of Roxbury, Vermont, Black Earth, Mazomanie, and Berry and the Village of Mazomanie. A portion of the Town of Blue Mounds is also included. In cooperative areas, data on wildfires is sparse and unorganized, which makes it essentially unavailable. Most of the data used in this assessment is derived from land under state jurisdiction for fighting wildfires. The ecology of the county lends itself to natural defenses from wildfires. Much of the county is covered by water or wetlands, or well developed with fire breaks. Less than 10 percent of the land in the county is expected to be impacted by wild land fires, making the geographic extent rating limited. Previous Occurrences From 1974 to 1998 Dane County has experienced 173 fires in the state managed extensive fire area, or about 7 fires a year. Many of the fires are smaller than an acre due to the number of roads that act as firebreaks and allow for fast response times by fire departments. For example, in the first three months of 2008, the Dodgeville Department of Natural Resources Dispatch Group, which includes only the north-western most portion of Dane County, experienced 24 fires with a total of acres burned, for an average fire size of only 5.5 acres. 47 Table 4.36 lists the documented wildfire incidents in Dane County that had fire areas greater than or equal to 10 acres. Table 4.36 County Wildfires =>10 acres Acres Year Month Day Cause Permit COST October 05 Unknown No $ April 16 Large Burn Yes $ April 18 Truck Not Needed $ April 16 Large Burn No $ May 03 Large Burn No $ March 02 Hike Not Needed $ March 24 Slash Yes $ March 19 Brush No $ March 20 Trash No $ March 31 Large Burn Yes $ 1, April 27 Unknown Unknown Unknown March 23 Unknown Unknown Unknown Source: Wisconsin Department of Natural Resources In 2003 there were two relatively large wildfires outside of the state managed area, the Deansville marsh fire that took place on April 27, 2003 and burned 500 acres, and the Town of Dunn marsh fire on March 23, 2003, which burned 110 acres. Though these fires were 47 Wisconsin Department of Natural Resources, Forest Fire Program Fire Report Website. Available online at accessed on March 23, Dane County 4.142

143 large, they posed little threat to life and property. Even within the context of recent fires, the chance of structural damage due to wildfire is extremely small. Available data shows that very few structures have ever been lost due to wildfires in the County. Relatively easy accessibility to fires and low fuel loads has likely provided first responders with an advantage in combating the blaze. Relying on wildfire data in the intensive fire areas of the County shown in Table 4.33, the average size of large fires (that is, fires encompassing at least 10 acres) is 71 acres and the average cost of response is approximately $450. These numbers give an indication that wildfire does not currently pose a significant threat to the safety of citizens and property in the County. Probability of Future Occurrences Based on the available data between 1975 and 2003, the assessment reflects wildfires 10 acres or more have a 42.9 percent (12 events over [divide by] 28 years) x 100) chance of occurrence and a likely occurrence rating. Smaller fires happen every year. Impact Assessments Direct Impacts Directly, fire endangers property and lives when it burns in an uncontrolled or unexpected manner. Fire is particularly dangerous when it encroaches into urban areas, or when it moves faster than fire suppression technology can cope. Sometimes, wildfires can exceed the warning time and evacuation capabilities of the population which greatly increases the direct impact on human life. Wildfires also exhibit a number of positive direct impacts, mostly connected to the continued renewal of a healthy ecological balance in natural areas. However, according to the Wisconsin Department of Natural Resources, almost all fires in Wisconsin are started by humans and are not, therefore, part of the natural ecologic process. Indirect Impacts Indirectly, wildfires create a significant drain on resources and manpower, as large fires are extremely complicated, require large commitments of resources and personnel, and may cause extensive personal and property damage. Historic fires in Wisconsin have wiped out entire communities (such as the city of Marshfield in 1887). While such fires are considered unlikely, the potential economic impact of wildfire on the state is enormous. These impacts cross County lines as well, by requiring the allocation and loan of resources across standard jurisdictional boundaries, sometimes even requiring national response support. Impact Magnitude and Severity Summary The size of wildfires in Dane County range from approximately 500 acres to a fraction of acre, most fires cover about 3 acres. Woodland and open lands, land that has the potential for wildfire, make up about 22 percent of the total acreage in the County. Much of Dane County is agricultural or urban land. How a fire will burn within the natural areas of the County is a complex phenomenon affected by wind, air temperature, humidity, fuel loads, fuel moisture, and topography. In densely wooded areas fires could destroy much in their path, fueled by high winds and high fuel loads. Other fires, such as those that might occur in a prairie ecosystem, burn Dane County 4.143

144 cooler along the ground and leave a dappled pattern of untouched areas within burnt areas. Fire prediction, though greatly aided by the development of new computer modeling programs, remains an imprecise science. Wildfire is also destructive when it interfaces with urban areas. Wildfire-vulnerable structures in Dane County are rare and the cost of fighting wildfires generally runs in the hundreds of dollars per response. Based on these assessments the overall impact magnitude and severity rating is considered minor. Vulnerability Assessment There are very few areas of the County where conditions indicate a high vulnerability to wildfires. Areas of higher relative vulnerability to wildfires are those in the urban/wildland interface, including: Areas where urban and suburban development is adjacent to open expanses of wild land areas. Mixed urban interface where isolated homes, subdivisions, or small communities are situated in predominantly wild land settings. Wild land/urban interface where islands of wild land vegetation occur inside a largely urban area. Areas that are hilly also can burn more readily. Fires run up hills igniting fuels more easily than on flat ground. Population The most exposed population are those living in the wildland-urban interface (WUI) zones, where residential properties are directly intruding into traditional wildland areas. The exposure of the population in these zones increases with the exposure of the corresponding general property, examined in the section below. Other exposed groups include children, the elderly, or those with breathing conditions who may be exposed to high levels of smoke. Approximately 35 percent of the County s population is exposed to the effects of wildfire due to age conditions alone. Populations living in long term care facilities or other skilled care facilities face additional exposures because of increased evacuation times and the potential that the population may be required to shelter in place. There are 15,827 licensed beds for hospitals, clinics, skilled care facilities, and other group homes or care locations that could be exposed to wildfire. These numbers represent the entire population exposure for the County, however, and a wildfire will only impact a selection of these numbers at any given time. Details on these figures can be found in Section 4.3 Vulnerability Summary. Overall, the vulnerability of the population to wildfires is low. General Property Any flammable materials are vulnerable during a wildfire, including structures and personal property. The vulnerability of general property increases as the distance of the property to wildfire-prone areas decreases, and is particularly high for structures located in the WUI. These structures receive an even higher level of vulnerability if the properties surrounding them are not properly mitigated for fire. Appropriate mitigation techniques include using non-flammable materials such as concrete for construction, leaving appropriate spaces between buildings and vegetation areas filled with non-flammable materials (such as decorative rock or stone), and clearing of underbrush and trees. However, the majority of general property is not located in these WUI zones and therefore experiences a minimal exposure to the hazard. If a wildland fire were to cross completely into an urban zone, the Dane County 4.144

145 damage would be extensive and there would likely be a higher exposure of property, but the geography and natural climate of Dane County make this event unlikely at this time. Overall, the exposure of general property in the County is low. Essential Infrastructure, Facilities, and Other Important Community Assets These aspects of the County may be exposed directly or indirectly to wildfire. Direct exposures are similar to those of General Property and increase as the infrastructure or facilities and capabilities moves into the WUI zone. Communications lines passing through susceptible areas such as forests are more exposed than those located in cities and other more urban areas. The indirect exposure of response capability increases seasonally and with the number of occurrences. Though the populations making up the response capability are not directly exposed to all fire events, the response of some of the personnel to an event lessens the capabilities overall for response to other emergency situations. If there is a large increase in the number of simultaneous wildland fires, even small ones, the response capability of the County could easily be compromised. This is not considered likely, however, and the overall vulnerability rating is low. Natural, Historic and Cultural Resources Some natural resources and natural areas may benefit from wildland fire, as at some level they must also be exposed to wildfire for a healthy ecological development of the area. Historic and cultural resources exhibit a vulnerability rating similar to those in general property, where vulnerability ratings increase the further into the WUI the property is, and the less mitigated the landscaping surrounding the property is. In addition, older buildings may be exempt from internal fire mitigation such as sprinklers and fire suppression technology, which may increase the vulnerability of the resource as a total loss once already on fire. Overall, the vulnerability rating is low. Estimating Potential Losses and Development Trends Assessment Potential Loss Estimates The potential for future damages is estimated by extrapolating data from past events. Future damages are expected to be very similar to past damages, with annual losses due to wildfire ranging in only the hundred s of dollars. The number of fires and the acres burned between 1974 and 2003 do not indicate that wildfires and their impacts are increasing. This data is limited to areas of the County that is regulated under the state Department of Natural Resources and therefore is a limited data set on which to base loss estimations. Development Trends The increasing development of Dane County indicates that encroachment into the WUI is possible. The 2007 Comprehensive Plan notes that density of residential building, which is the primary transgressor into the WUI zone, has increased over the last forty years and is predicted to increase well into In addition, the plan cites the numerous firebreaks created by roads and other development as a mitigating factor in wildfire events. However, the 2007 Comprehensive Plan also notes that scattered development patterns tend to fragment the landscape, destroying connections between open areas, creating edge effects that increase points of contact between incompatible uses, and creating a variety of cumulative, indirect impacts to natural and agricultural resources. Over time, if cumulative impacts reduce habitat, agricultural areas, or both, below a critical mass of contiguous, similar area, the local ecosystem or agricultural economy may collapse. Many of the Dane County 4.145

146 policies in Volume I of the Dane County Comprehensive Plan seek to increase residential and commercial density, encourage redevelopment, and promote compact development clustered near existing urban or developed areas as a way of reducing fragmentation. These policies may aid in minimizing WUI encroachment. Overall Risk Summary There is limited data indicating that general structures, critical facilities or populations have been or will be harmed by wildfire in the County. While the potential exists for damaging wildfires, many natural and man-made fuel breaks exist. Overall, then, the vulnerability of the County to wildfire is low. Table 4.37 provides the methodology for how all aspects of the hazard profile were evaluated to establish an overall hazard rating. Table 4.37 Risk Summary for Wildfires Measurement Rating Value Geographic Extent Limited 1 Probability of Future Occurrence Likely 3 Vulnerability Assessment Low 1 Impact Magnitude and Severity Minor 1 Overall Risk Rating Low Windstorms Description Damaging winds occur relatively frequently across Wisconsin, usually in association with severe thunderstorms. While many people immediately associate wind damage with tornadoes, thunderstorm straight-line wind and strong, widespread, non-thunderstorm winds, both up to hurricane force, can result in extensive damage as well. These winds can become hurricane-force in the worst cases. Table 4.37 lists relative wind speeds and anticipated effects. Additionally, Wisconsin experiences another kind of wind damage: nonthunderstorm, widespread high wind behind cold-frontal passages in the wake of strong synoptic-scale low pressure systems. Severe thunderstorms develop powerful updrafts and downdrafts. An updraft of warm, moist air helps to fuel a towering cumulonimbus cloud reaching tens of thousands of feet into the atmosphere. A downdraft of relatively cool, dense air develops as precipitation begins to fall through the cloud. Winds in the downdraft can reach in excess of 87 knots (kts) or 100 miles per hour (mph). When the downdraft reaches the ground it spreads out forming a gust front: the strong, often refreshing wind that kicks up just before the storm hits. As the thunderstorm moves through the area, the full force of the downdraft (called a downburst in strongest cases) in a severe thunderstorm can be felt as horizontal, straightline winds with speeds well over 44 kts (50 mph). Basically, severe thunderstorms in Wisconsin can produce wind gusts to 50 to 130 knots (58 to 150 mph) per National Weather Service and NCDC data. Dane County 4.146

147 Straight-line winds are currents of air in which the ground-relative motion does not have any significant curvature. They are used in the context of surface winds that inflict damage; to be distinguished from winds in tornadoes, which have significant curvature. 48 Straightline winds are often responsible for most of the damage associated with a severe thunderstorm. Damaging straight-line winds occur over a range of scales. At one extreme, a severe single-cell thunderstorm may cause localized damage from a microburst, a severe downdraft extending not more than about two miles across. In contrast, a powerful thunderstorm complex that develops as a squall line can produce damaging winds that carve a path as much as 100 miles wide and 500 miles long. The non-thunderstorm, widespread high wind events usually occur during the cooler part of the year, from October through April. During this time of the year, the atmospheric pressure differences between high pressures and low pressures are maximized. This results in tighter pressure gradients which generates stronger surface winds. These nonthunderstorm high wind events usually have wind gusts to 50 to 87 knots (58 to 100 mph) that can persist for 6 to 18 hours over large areas. Severe thunderstorm wind events can inflict considerable damage on trees, power-lines, and other wooden structures. Strong, widespread, non-thunderstorm winds sometimes affect most of Wisconsin in the wake of a deep low pressure system moving through the Great Lakes region. Meteorologists use the term "High Wind" to describe these situations, which can consist of 10 to 18 hours of steady wind speeds of 30 to 45 mph with occasional gusts to 60 to 100 mph. Table 4.38 Wind Speeds and Effects Wind Speed (kts) Wind Speed (mph) Wind Effects Large branches in motion Whole trees in motion, inconvenience in walking against the wind Twigs and small branches break off trees, difficulty in walking against the wind, high profile vehicles such as trucks and motor homes may be difficult to control Potential damage to antenna structures, wind may push over shallow rooted trees, especially if the soil is saturated Potential for minor structural damage, particularly to manufactured homes, power lines, trees, and signs may be blown down Moderate structural damage to walls, roofs, and windows, trees blown down, and manufactured homes may be destroyed Extensive damage to walls, roofs, and windows, trees blown down, moving vehicles pushed off roads Extreme damage to structures and roofs, trees uprooted or snapped. Greater than 135 Greater than 155 Catastrophic damage, structures destroyed. Source: National Weather Service Spotters Guidance Hurricane force winds are defined as a speed equal to or greater than 64 knots (74 mph) or Beaufort Number 12 (Force 12). Hurricane-force winds are not exclusive to hurricanes; they 48 American Meteorological Society, Glossary of Meteorology, 2 nd Edition. Available online at last accessed February 11, Dane County 4.147

148 occur quite often in strong non-tropical storms such as the northeaster, or even in severe thunderstorms. 49 Geographic Extent Damaging windstorm events may occur anywhere in Dane County. As with severe thunderstorms, blizzards, hail, or tornados, there are no geographic features within Dane County that naturally lower the risk of a windstorm event. Therefore, the geographic extent rating of the hazard may be considered uniform. However, when damaging wind occurs, it may or may not affect the entire County. Damage associated with a severe thunderstorm tends to be a geographically isolated event, affecting only small areas of several square miles at any one time. On the other hand, widespread, non-thunderstorm high winds can affect much of the county. But since any area of the county can experience damaging windstorms, the geographic extent rating for windstorms is extensive. Previous Occurrences The National Climactic Data Center database documented 297 severe thunderstorm wind events in Dane County between 1956 and 2008, or an average of 5.7 events per year. Of these, only 176 documented windspeed, which makes comparative analysis slightly skewed. However, based on the 176 available windspeeds, Dane County has experienced 151 events with windspeeds in excess of 50.4 kts (58 mph), which the National Weather Service defines as a severe thunderstorm wind. 22 events have equaled or exceeded 64 kts (74 mph), which are categorized as hurricane-force winds. The average wind speed during severe thunderstorm wind events, based on this data, is 56 kts (65 mph). Figure 4.29 indicates the number of severe thunderstorm wind events for Wisconsin, divided by county, from 1982 to Figure 4.30 identifies the number of events, by county, where thunderstorm wind speeds exceeded 100 mph (87 kts) since In 1998, a High Winds and Severe Storms disaster was declared in the county, but no state or federal aid declarations were awarded. 50 In more recent years, these records have been kept in greater detail, including a description of the event and the resulting impacts. The NCDC database records two, non-thunderstorm high wind deaths for Dane County (one in 1997 and one in 1998), and 2 injuries (1998). The NCDC database also indicates cumulative estimated damage costs of $18.9 million for severe thunderstorm winds and non-thunderstorm high winds. The NCDC website provides the following descriptions of significant high wind events affecting Dane County. April 6, 1997 Strong gradient winds, enhanced by scattered snow showers (transfer of higher level momentum downward to surface by mixing), resulted in scattered damage reports. In Sun Prairie, the high winds, measured at 66 mph, blew open a glass door in a restaurant. The glass debris struck and injured an elderly woman, who died from the injuries the next day. The Madison TV-3 weather station recorded a peak wind gust of 71 mph at 1715 CST. In the civil Town of Dane, a gust of 61 mph was noted. Southeast of Mount Horeb, the high winds forced the collapse of a barn. A camper vehicle was tipped over on by the powerful winds on 49 Ibid. 50 Wisconsin Emergency Management Dane County Disasters. Available online at last accessed February 11, Dane County 4.148

149 Highway 113. The high winds also toppled large trees in scattered areas across the entire county. One tree in Monona fell against a home and damaged its siding and windows. Power outages were noted. People described the wind-driven debris as "missiles flying through the air." May 31, 1998 During the early morning hours of Sunday, May 31st, south-central and southeast Wisconsin experienced an unprecedented, widespread downburst wind event known as a "derecho." Incredibly powerful, hurricane-force straight-line winds, with peak gusts of 100 to 128 mph tore through 12 counties in this part of the state, while another 8 counties had peak gusts of 60 to 80 mph. Meteorologically, a solid squall line developed in southern Minnesota and gathered strength as it raced east with a translational speed of 50 to 60 mph across southcentral and southeast Wisconsin. The squall line was orientated southwest to northeast and had many microbursts and macrobursts embedded in it. Utility companies and Emergency Managers stated that this was the most damaging, widespread, straight-line thunderstorm wind event to affect southern Wisconsin in the past 100 years. About 60,000 customers were without electricity in south-central Wisconsin, and about 170,000 in southeast Wisconsin. Some residences or businesses were without power for many as 6 days. Hundreds or motor vehicles were damaged or destroyed by falling trees and branches or collapsed garages. Dane County measured gust of 100 mph in Marshall, but peak gusts estimated at mph based on damage. The hardest hit areas were Waunakee- DeForest, Sun Prairie, and Marshall. Cars were blown sideways off I-94 north of Madison. Two people injured in Marshall by flying debris as roof was torn off their home. A total of 300 residences had minor damage, 18 major, and 1 was destroyed. One business had minor damage, and 7 had major damage. Twenty farm buildings sustained minor damage, 12 major, and 15 were destroyed. November 10, 1998 Screaming high winds raked south-central and southeast Wisconsin counties for about 17 hours, resulting in widespread damage to thousands of trees, homes, businesses, power poles, power lines, street lights, road signs, fences, flagpoles, barns, sheds, crops, boats, cars, trucks, campers, trains, airport hangars, and airplanes. Estimated monetary damages were $10.31 million in property damage and $1.625 million in crop damage. The sustained southwesterly winds of 30 to 40 mph gusted to 60 to 70 mph, with isolated gusts to around 80 mph. These relentless winds eventually caused 125,000 customers to lose electrical power. So many poles and lines were toppled that some customers were without power for 3 to 4 days. In Dane County an 87 year-old man was killed after being hit by a car that was blown sideways on the north side of Madison. Several businesses in Madison, Mt. Horeb, and Stoughton sustained damages. In Monona, a roof was torn off a multi-unit apartment building and four other nearby buildings were also damaged. Several dozen semi-trucks were overturned on I-90/94, US-18/151, and US 51 highways. July 6, 2003 Two rounds of scattered severe convection affected south-central and southeast Wisconsin on Sunday, July 6, The first round occurred during the morning hours and the second during the late afternoon hours. Powerful, downburst, damaging, straight-line winds toppled large trees and/or power-lines, 4 weak tornadoes spun up, a separate funnel cloud was reported, and there were a couple occurrences of large hail. Detailed descriptions of the four tornadoes can be found in separate reports. Probably the hardest-hit area extended from Middleton (Dane Co.) to Maple Bluff. In the Maple Bluff area, 8 homes sustained minor wind Dane County 4.149

150 damage, and toppled trees damaged a car and two boats or large branches during the morning round. Wind gusts in the Maple Bluff area were estimated to briefly reach 65 knots (75 mph). Lightning struck a home in Middleton, resulting in a roof/attic fire. July Powerful thunderstorm wind gusts toppled large trees and broke branches that brought down some power-lines. In McFarland, a house was blown down, and tree debris damaged a restaurant. Two rounds of severe weather affected south-central and southeast Wisconsin on July 10th. An initial cluster of storms north of the Milwaukee area in Ozaukee County pulsed to severe limits and generated large hail up to 3/4 inch in diameter during the early afternoon hours. A second round of severe weather was associated with several clusters or short bowing segments of lines of storms that moved west to east across southern Wisconsin during the late afternoon and evening hours. Veering winds allowed for the development of rotating updrafts in a couple cells that generated two weak tornadoes. Otherwise, the severe weather type was powerful downburst winds. Dane County 4.150

151 Figure 4.29 Severe Thunderstorm Winds by County Source: National Weather Service Dane County 4.151

152 Figure mph+ Thunderstorm Winds by County Source: National Weather Service Dane County 4.152