Outline. Precipitation. How would you describe precipitation patterns in your area? Bottom line: one-page summary

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1 Outline Precipitation June 13, 2013 Phoenix, AZ Measuring rainfall Patterns of precipitation in time and space Predicting precipitation Patterns related to extreme events (floods & drought) Paleo-climate indicators Climate patterns (ENSO) Sources of information about precipitation and climate CLIMATE is what you expect, WEATHER is what you get R.A. Heinlein 1 2 Bottom line: one-page summary Precipitation varies seasonally depending on fetch and storm type. Precipitation varies by location, mainly due to orographic effects. Tropical storms give rise to the biggest floods. Extended periods of drought are normal in S, as evidenced by tree rings. Rocky Mt snowpack is critical to our water supply El Nino teleconnections can result in wetter winters for southern AZ How would you describe precipitation patterns in your area? A. It only rains much in the summer. B. It only rains much in the winter. C. Rain storms during Jul-Aug or Dec-Feb are fairly similar. D. Rain storms during Jul-Aug or Dec-Feb are quite different. 3 4

2 How important is rainfall? AZ ~ 140,000 mi ac/mi 2 => 89.6 Mac Precip ~ 1 ft/yr => 89.6 Maf Where does it go? Runoff ~ 1.8 Maf => Evap. ~ 98 % 5 How does precipitation vary in time and space? What areas get the most precipitation and why? Why are summer storms different from winter storms? 6 Sources of Precipitation % Precipitation in Winter (Oct-Mar) Where does our precipitation come from? High Variability in Space and Time Precipitation influenced by rough mountains. Winter: Large scale storms from the Pacific Ocean. Important for water supply and snow. Summer:Complex convective storms, very heterogeneous, intense. High evaporation. % Precipitation in Summer (July & Aug) E. Pacific Ocean Gulf of California Moisture from the Gulf of Mexico 7 8

3 Types of Precipitation Daily Patterns Sep. vs Feb. Frontal/synoptic Convective 9 10 rainlog.org Annual variability of temp/precip Annual variability of temp/precip - TUS 11 weatherspark.com/history/31809/2012/tucson-arizona-united-states 12

4 Annual variability of temp/precip - PHX What factors control precipitation in the SW? weatherspark.com/history/31259/2012/phoenix-arizona-united-states The University of Arizona 14 Orographic Pattern to SWE Annual Patterns of Precipitation

5 Orographic Precipitation: related to mixing ratio & lapse rate Which is the best explanation of orographic precipitation? A. Precipitation that occurs where moist oceanic air is forced over coastal ranges. B. The increased likelihood that higher areas will receive more precipitation. Saturated Mixing Ratio C. Precipitation that occurs where moist air cools and condenses as it is forced to rise over higher elevations. D. Precipitation that happens over mountains. Source: www-unix.oit.umass.edu Sources of excess runoff Unusual supplies of moisture What causes extreme events? What patterns do we see in Floods and Droughts? Stationary storm tracks Tropical storms / Hurricanes Rain on snow / Rapid melt Saturated ground 19 20

6 Factors Affecting Flooding Persistence and intensity of precipitation Soil moisture conditions Surface cover forested to bare Permeability sandy/tilled to compacted Storm/Runoff Classification Summer Convective Tropical Winter Synoptic 21 Source: AHIS, Hirshbeck 22 Storm/Runoff Statistics Tropical Storm & Monsoon-related floods Oct 1-2, 1983 STORM PRECIPITATION TOTALS: Tucson: 6.40" PEAK FLOWS: San Pedro R near Tombstone: 13,600 cfs San Pedro Winkelman: 135,000 cfs Gila Kelvin: 100,000 cfs (10/02/83) Santa Cruz Tucson: 52,700 cfs Rillito Creek near Tucson: 29,700 cfs Santa Cruz Cortaro: 65,000 cfs Tropical Frontal Convective 23 24

7 Phoenix/Salt Historic Floods 1891 (feb) 300,000 cfs 1905 (nov) photo => 1916 (jan) 100,000 cfs 1937 (feb) 88,000 cfs 1941 (mar) 117,000 cfs 1952 (jan) 111,000 cfs 1965 (dec) 69,000 cfs; all bridges damaged 1967 (aug) Katrina 1970 (sep) Norma 1972 (oct) Joanne ; 70,000cfs 1978 (mar) 89,500 cfs; 122,000 cfs 1978 (nov) 140,000 cfs 1979 (jan) 96,000 cfs; 54,000 cfs 1980 (jan) 170,000 cfs; 99,000 cfs; 64,000 cfs; 11/13 bridges damaged 1983 (oct) Octave ; 60,000 cfs; 33,000 cfs 1993 (jan) El Nino; 143,000 cfs; 34,500 cfs 2005 (all summer) 2-3 events; 46,500 cfs 2008 (jan) 81,300 cfs 2010 (jan) 1-5 ; 88,300 cfs; 32,000 cfs Black cfs PHOENIX est? USGS SALT RIVER NEAR ROOSEVELT, AZ USGS SALT RIVER BLW STEWART MOUNTAIN DAM, AZ 25 Factors Affecting Drought Severity & Impact Dryness Warmth Persistence Soil moisture conditions Availability of alternative water supplies Ability to fallow land or curtail use 26 PDSI The Palmer Drought Severity Index responds to abnormally wet(+) or dry(-) weather conditions. Drought Indicators The index is a sum of the current moisture anomaly and a portion of the previous index to include the effect of the duration of the drought or wet spell. The moisture anomaly is the product of a climate weighting factor and the moisture departure. It is slow to detect fastemerging droughts, and does not reflect snowpack

8 Drought Monitor historical droughtmonitor.unl.edu/archive.html

9 SW Climate Outlook accessed 5/ Which one of the following best describes Drought Monitor Maps? A. They can change rapidly, depending upon recent precipitation. B. They incorporate local soil & precip. conditions. C. The index is reset every winter. D. Correspond with maps of shallow soil moisture. Paleo climate indicators How do we determine climate for time before we took measurements? 35 36

10 Early wood Dendrochronology - Tree Ring Basics Late wood Tree ring width based on: soil moisture conditions soil and air temperatures sunshine Crossdating: matching ring-growth across many samples allows construction of continuous record of growing conditions from discontinuous sample of tree rings. Skeleton Plots: adjustment for local variation 37 Tree-ring and Streamflow Correlation ???????????????????????????? Discharge (cfs) Colorado Lee s Ferry Woodhouse et al. (2006) Annual Avg Flow for the Gila Coolidge Dam Year Tree-rings correlate to certain climate events Especially El Niño & La Niña events Significance: Tree-rings have a longer period of record than most streamflow 38 & precipitation data sets Calibration, Validation, Reconstruction Upper Basin persistent drought RMSE ~ 2.5 Maf WYN2K: Persistent drought is a normal and cyclic characteristic of the Southwest treeflow.info/upco/coloradoleesmeko.html Persistent drought (two or more years) in regional flow reconstructions, Values are shown only for years with two or more values consecutively below the median. (Woodhouse & Lukas, Climate Change, 2006) 39 40

11 Monsoon Predictability Griffin et al., GRL (2013) WYN2K: Weak relationship between cool and monsoon season events Dry Times Ahead (Overpeck and Udall, Science 25 June 2010, V.328(5986) pp ) Eos, Vol. 89, No. 9, 26 February 2008 MacDonald, UCLA Taken together, climatological and paleoclimatological evidence does not provide any reason to conclude that events such as the early 21st-century drought could not persist longer than the 5- to 8-year duration of historical droughts of the twentieth century. Prolonged episodes of aridity persisting for a decade or more are apparent in many paleohydrological records, and conditions in the Pacific appear to have played a key role in these episodes. 43 Reduced late season snowpack Drying faster/more than climate change models indicate Colo. River flow decrease 20% by 2050? Chance of loss of Powell/Mead storage now 3 in 10 Recommendation: Learn to live with less Climate change adaptation 44

12 Where does our water supply come from? Predicting Water Supplies How predictable are our water supplies? How does uncertainty in precipitation affect water resources? A. Snowmelt B. Groundwater C. Water reuse D. All of the above Recent Water Supply Forecast Map Feb. Water Supply Outlook

13 Impact of Climate Change Likely changes: Warmer temperatures Less snowpack? Earlier runoff Increased water demand Longer growing season More ET; less SM Warmer water WQ issues What are El Niño & La Niña events? Changes(+/-) in normal sea surface temp. (>0.5 C) Longer-term climate patterns that might lead to greater predictability Eastern Pacific: El Niño: increase (+), warmer water temperature La Niña: decrease (-), cooler water temperature Watch Areas

14 Tele connections El Niño = Wet in Southwest US Warm winter storms are more common during El Nino monitoring/ensocycle/enso_cycle.shtml Below average flows in the CR are more common during La Nina La Niña = Dry in Southwest US 53 WYN2K: ENSO has a ~2-4 year cycle 54 Relative Performance Can you interpret this? WYN2K: ENSO predictions are poor beyond 6 months 55 iri.columbia.edu/climate/enso/currentinfo/quicklook.html 56

15 Effect of ENSO on Winter Precip. in AZ Gila Calva Daily Winter Streamflow (cfs) Climate variability: spatial, interannual, regimes (decadal), climate change All EL NINO Years ( ) Precipitation during El Nino Winters Credit: Tom Pagano All LA NINA Years ( ) 57 see also: Effect of OLR, Climate, 2012 journals.ametsoc.org/doi/abs/ /jcli-d What is our current predictability of ENSO? AZ Cooperative Extension A. Month to month. B. 6 months. C. 2-4 years D. Decadal 59 cals.arizona.edu/climate 60

16 Bottom line: one-page summary Precipitation varies seasonally depending on fetch and storm type. Precipitation varies by location, mainly due to orographic effects. Tropical storms give rise to the biggest floods. Extended periods of drought are normal in S, as evidenced by tree rings. Rocky Mt snowpack is critical to our water supply El Nino teleconnections can result in wetter winters for southern AZ 61