David R. Vallee Hydrologist-in-Charge NOAA/NWS Northeast River Forecast Center

Transcription

1 Flooding along the Housatonic River following Tropical Storm Lee, Sept 8, Photo: A. Driscoll, Connecticut Post David R. Vallee Hydrologist-in-Charge NOAA/NWS Northeast River Forecast Center

2 Examining some of our extreme events of the past 10 years Big Rainstorms & High Impact Floods Flash Drought Episodes How may a changing climate be impacting flood behavior Accumulation of Ingredients not one single source The importance of Land Trusts and Land Preservation as a means for reducing impacts

3 NOAA/NWS s Northeast River Forecast Center Our Mission: To provide our nation with river, flood and water resource forecasts for the protection of life and property and the enhancement of the national economy

4 A Look At Current & Future Water Prediction Services: Moving from Point Specific to Street Level Hydrologic Forecasting New National Water Model Building a Weather-Ready Nation

5 National Water Model Based Street Level Hydrologic Prediction Record Setting West Virginia Floods, 6/23/2016 Thousands of homes damaged or destroyed, $111+ million in FEMA aid NWM allows users to drill down from regional to local to street scale Information complements hydrologic guidance at existing forecast locations and provides new insight at millions of hydroblind locations NWM Street-Level Forecast Streamflow (cfs) Hydro-Blind location 500 people trapped at Elkview mall Bridge Collapse NWM 15 hr Regional Streamflow Anomaly Forecast, Valid 20Z 6/23 Experimental NWM Local Inundation Map Building a Weather-Ready Nation Shading indicates flooded areas

6 Record flooding along the Fish and Saint John Rivers northeast Maine, 4/30/2008 St-Jean-sur-Richelieu, Quebec, Canada, 5/6/11 Photo: AP//Canadian Press, R. Remoirz Providence Street West Warwick, RI at 1030 am Wednesday 3/31/10 Damage along Schoharie Creek, Prattsville, NY T.S. Irene, Photo: J. Vielkind / Times Union

7 Several: Slow moving weather systems a blocked up atmosphere Related to loss of artic ice cover Multiple events in close succession or one big slow moving storm Results in saturated antecedent conditions before main event Each fed by a tropical connection Plumes of deep moisture

8 Modest changes in air & sea temperatures = atmosphere can hold more moisture New England is in close proximity to the Gulf & Atlantic moisture streams Affected by dual storm tracks and blocking high pressure over Greenland These ingredients offer us more opportunities to latch onto plumes L L L H L Reduction of Arctic sea ice changes upper level wind flow Arctic Amplification Blocked up pattern induces slower moving storms or back-to-back-to back events

9 Common themes across New England and Connecticut: Increasing annual precipitation Increasing frequency of heavy rains Warming annual temperatures Shift in precipitation frequency Trend toward increased flood magnitude and/or frequency Most pronounced where significant land use change and/or urbanization has occurred More pronounced in smaller river basins Residents are rescued from their homes by boat along flooded Pawcatuck River, Westerly RI, on March 30, Photo: Major flooding along Route 7 from the Housatonic River in New Milford, CT on March 11, Source: Ctcameraeye.com

10 +1 F / 33 yrs

11 +1 inch / 27 yrs

12 NOAA ATLAS Hour 100 year return period rainfall Much of southern NE experienced a 1 to 2 inch upward shift! 7 7 Thick yellow lines represent 24 hr 100 yr values from TP-40,

13 Since the late 60s, signature of less frequent & shorter dry periods and longer, more frequent and intense wet periods

14 Changes in frequency/magnitude Part land use/urbanization Compounded by encroachment in the floodplain Part changing climate Larger basins & those with flood control haven t seen as noticeable a shift Greater capacity to handle more rain Greater capacity to control releases Northern and western parts of the state are seeing the most dramatic increase in flooding Same area where 100 year rainfall has shifted dramatically Flooding along the Housatonic River following Lee, Sept 8, Photo: A. Driscoll, CT Post Moderate flooding along Connecticut River, April 1 st, Photo: NBC Connecticut

15 Number of Floods Per Year Southern New England River Basin Normalized Number of Minor, Moderate, and Major Floods Prior to 1970 Data provided by 2.4 Major Floods 2 Moderate Floods Minor Floods Location

16 Number of Floods Per Year Southern New England River Basin Normalized Number of Minor, Moderate, and Major Floods from Data provided by 2.4 Major Floods 2 Moderate Floods Minor Floods Location

17 Number of Floods Per Year Lower Connecticut Basin Normalized Number Of Minor, Moderate, & Major Floods Per Year Prior to 1970 Data provided by Major Floods Moderate Floods Minor Floods MNTM3 INDM3 WSFM3 TMVC3 TARC3 HFDC3 MDDC3

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19 Common themes across New England and Connecticut: Increasing annual precipitation Increasing frequency of heavy rains Warming annual temperatures Shift in precipitation frequency Trend toward increased flood magnitude and/or frequency Most pronounced where significant land use change and/or urbanization has occurred More pronounced in smaller river basins Residents are rescued from their homes by boat along flooded Pawcatuck River, Westerly RI, on March 30, Photo: Major flooding along Route 7 from the Housatonic River in New Milford, CT on March 11, Source: Ctcameraeye.com

20 Floodplain, land use, infrastructure, dam spillway requirements, drainage requirements, storm water management, non-point source runoff, bridge clearances, hardening of critical facilities in the floodplain, property values etc Flood Insurance work to increase participation How much risk are we willing to insure and accept? Graphic courtesy of Cameron Wake University of New Hampshire

21 Land Trusts can help to: Preserve the land Retain and restore grounds to their natural state Increase rainfall/runoff storage capacity of a given parcel of land Improve water quality through restoration of lands and vegetation to a more natural state Reduce storm water runoff Neponset Basin Wetland Restoration. Photo: MA Exec. Office Env. Affairs

22 Flooding along the Housatonic River following Tropical Storm Lee, Sept 8, Photo: A. Driscoll, Connecticut Post David R. Vallee Hydrologist-in-Charge NOAA/NWS Northeast River Forecast Center

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24 WFO Caribou, ME Northeast Maine counties WFO Gray, ME Southwest Maine and all of New Hampshire WFO Burlington, VT Northern 2/3 rds of VT WFO Albany, NY Srn 1/3 of VT, Berkshire, MA, Litchfield, CT WFO Taunton, MA Rest of MA, all of RI, and the northern 2/3 rds of CT WFO Upton, NY All coastal CT Counties WFO Binghamton, NY Finger Lakes region WFO Buffalo, NY Buffalo Creeks, Genesee and Black

25 Requirements: Observed precipitation & temperatures Observed streamflows (USGS) Forecast temperatures and precipitation Drainage area 100 sq mi Our models help us forecast: The volume of water in the river & that s converted to stage/elevation Time of the peak elevation & duration Soil moisture & Snow melt Unit hydrograph theory Reservoir Operations Hydraulics (HES-RAS) for complex river systems Tidal reaches Lake Champlain, Farmington River Combines tidal/storm surge with fresh water runoff on 5 tidal rivers

26 The number of degrees that a day's average temperature is below 65 o Fahrenheit (18 o Celsius), the temperature below which buildings need to be heated

27 The number of degrees that a day's average temperature is above 65 o Fahrenheit and people start to use air conditioning to cool their buildings

28 Change in Precipitation Patterns Intense precipitation events (the heaviest 1%) in the continental U.S. increased by 20% over the past century while total precipitation increased by 7% ( ). Source: 29

29 >11

30 The Northeast U.S. has become a hot spot for record floods & heavy rainfall in the past 20 years Noticeable trends include increased yearly rainfall and increased annual temperatures Smaller watersheds & those with significant urbanization and/or land use change are most vulnerable to increased river & stream flooding Continued sea level rise combined with intense coastal storms has renewed the coastal flood threat A weaker category of storm is now capable of producing inundation once limited to the more intense hurricanes and coastal storms

31 Droughts of yesteryear: Prolonged record lows Not as record as today s low minimum flows But far longer in duration with little significant recharge Short/intense drought episodes: Record daily flows Exceeding minimums during the 1960s drought! But very short duration with long periods of significant recharge if not flood volumes

32 2009 study of 28 watersheds with minimal human influences Results indicate basins have experienced increased peak annual flows Strongest statistical trends noted by the large blue triangles 2011 study of 23 watersheds with minimal human influences Examined peaks over defined thresholds per water year More frequent flooding at 22 of 23 locations Increasing flood magnitude at 17 of 23 locations Spatial distribution of trend directions & magnitudes for based with minimal human influences. Reference: M. Collins, Journal of The American Water Resources Association (JAWRA) April Spatial Distribution of Flood Frequency as measured by peaks over threshold per water year. Reference: W. Armstrong, M. Collins, and N. Snyder Journal of The American Water Resources Association (JAWRA) April 2011.