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Hydrologic Implications of Climate Change for the Western U.S., Pacific Northwest, and Washington State Alan F. Hamlet •JISAO/CSES Climate Impacts Group •Dept. of Civil and Environmental Engineering University of Washington Recession of the Muir Glacier Aug, 13, 1941 Aug, 31, 2004 Image Credit: National Snow and Ice Data Center, W. O. Field, B. F. Molnia http://nsidc.org/data/glacier_photo/special_high_res.html Global Climate Change Scenarios for the PNW Consensus Forecasts of Temperature and Precipitation Changes from IPCC AR4 GCMs 21st Century Climate Impacts for the Pacific Northwest Region Mote, P.W. and E. P. Salathe Jr., 2009: Future climate in the Pacific Northwest (in review) PDO Effects of the PDO and ENSO on Columbia River Summer Streamflows 450000 Cool Cool 350000 300000 250000 200000 Red=warm ENSO Green=ENSO neutral Blue=cool ENSO 2000 1990 1980 1970 1960 1950 1940 1930 1920 1910 150000 1900 Apr-Sept Flow (cfs) Warm Warm 400000 Snowpack Schematic of VIC Hydrologic Model and Energy Balance Snow Model Snow Model Trends in April 1 SWE 1950-1997 Mote P.W.,Hamlet A.F., Clark M.P., Lettenmaier D.P., 2005, Declining mountain snowpack in western North America, BAMS, 86 (1): 39-49 DJF avg T (C) Overall Trends in April 1 SWE from 1947-2003 Trend %/yr Trend %/yr Hamlet, A.F., Mote, P.W, Clark, M.P., Lettenmaier, D.P., 2005: Effects of temperature and precipitation variability on snowpack trends in the western U.S., J. of Climate, 18 (21): 4545-4561 DJF avg T (C) Temperature Related Trends in April 1 SWE from 1947-2003 Trend %/yr Trend %/yr Hamlet, A.F., Mote, P.W, Clark, M.P., Lettenmaier, D.P., 2005: Effects of temperature and precipitation variability on snowpack trends in the western U.S., J. of Climate, 18 (21): 4545-4561 DJF avg T (C) Precipitation Related Trends in April 1 SWE from 1947-2003 Trend %/yr Trend %/yr Hamlet, A.F., Mote, P.W, Clark, M.P., Lettenmaier, D.P., 2005: Effects of temperature and precipitation variability on snowpack trends in the western U.S., J. of Climate, 18 (21): 4545-4561 Plotting Areas of High Hydrologic Disturbance Elsner et al., 2009: Implications of 21st Century climate change for the hydrology of Washington State (in review) Change in Long-Term Mean April 1 SWE in WA -29% -27% -44% -37% -65% -53% Elsner et al., 2009: Implications of 21st Century climate change for the hydrology of Washington State (in review) Changes in Seasonal Streamflow Timing Simulated Changes in Natural Runoff Timing in the Naches River Basin Associated with 2 C Warming 120 Simulated Basin Avg Runoff (mm) 100 80 Impacts: •Increased winter flow •Earlier and reduced peak flows •Reduced summer flow volume •Reduced late summer low flow 1950 60 plus2c 40 20 0 oct nov dec jan feb mar apr may jun jul aug sep Projected Streamflow Timing Shifts in Washington Historical and Projected 21st Century Flows for the A1b Scenario 6000 historical Simulated Natural Flows (cfs) 2020A1b 5000 2040A1b 2080A1b 4000 3000 2000 1000 Chehalis River 0 oct nov dec jan feb mar apr may jun jul aug sep Historical and Projected 21st Century Flows for the A1b Scenario 6000 Simulated Natural Flows (cfs) historical 2020A1b 5000 2040A1b 2080A1b 4000 3000 2000 1000 Quinault River 0 oct nov dec jan feb mar apr may jun jul aug sep Historical and Projected 21st Century Flows for the A1b Scenario 3500 Simulated Natural Flows (cfs) historical 2020A1b 3000 2040A1b 2080A1b 2500 2000 1500 1000 500 Elwah River 0 oct nov dec jan feb mar apr may jun jul aug sep Historical and Projected 21st Century Flows for the A1b Scenario 35000 Simulated Natural Flows (cfs) historical 2020A1b 30000 2040A1b 2080A1b 25000 20000 15000 10000 5000 Skagit River 0 oct nov dec jan feb mar apr may jun jul aug sep Historical and Projected 21st Century Flows for the A1b Scenario 12000 Simulated Natural Flows (cfs) historical 2020A1b 10000 2040A1b 2080A1b 8000 6000 4000 2000 Yakima River 0 oct nov dec jan feb mar apr may jun jul aug sep Climate Change Will Result in Widespread Transformation of Snowmelt and Transient Watersheds to Rain Dominant Watersheds Mantua, N., I. Tohver, A.F. Hamlet, 2009: Impacts of climate change on key aspects of freshwater salmon habitat in Washington State, (in review) Changes in Hydrologic Extremes Regionally Averaged Temperature Trends Over the Western U.S. 1916-2003 3.00 PNW Linear Trend (Deg. C per century) CA PNW 1.50 1.00 0.50 0.00 -0.50 -1.00 nov dec jan feb mar apr may jun jul aug sep 4.00 Linear Trend (Deg. C per century) CA CRB GBAS 2.00 oct GB CRB Tmax 2.50 CA 3.50 CRB Tmin GBAS 3.00 PNW 2.50 2.00 1.50 1.00 0.50 0.00 oct nov dec jan feb mar apr may jun jul aug sep DJF Avg Temp (C) Simulated Changes in the 20-year Flood Associated with 20th Century Warming DJF Avg Temp (C) X20 2003 / X20 1915 X20 2003 / X20 1915 X20 2003 / X20 1915 Summary of Flooding Impacts Rain Dominant Basins: Possible increases in flooding due to increased precipitation intensity, but no significant change from warming alone. Mixed Rain and Snow Basins Along the Coast: Strong increases due to warming and increased precipitation intensity (both effects increase flood risk) Inland Snowmelt Dominant Basins: Relatively small overall changes because effects of warming (decreased risks) and increased precipitation intensity (increased risks) are in the opposite directions. Future Projections of Flood Risk in Washington •Floods in western WA are expected to increase in magnitude due to the combined effects of warming and increasingly intense winter storms. •In other parts of the State, changes in flooding are smaller, and in eastern WA projected reductions in flood risk are common due to loss of spring snow cover. Mantua, N., I. Tohver, A.F. Hamlet, 2009: Impacts of climate change on key aspects of freshwater salmon habitat in Washington State, (in review) Changes in Low Flow Risks 7Q10 values are projected to systematically decline in western WA due to loss of snowpack and projected dryer summers Mantua, N., I. Tohver, A.F. Hamlet, 2009: Impacts of climate change on key aspects of freshwater salmon habitat in Washington State, (in review) Landscape Scale Disturbance Annual area (ha × 106) affected by MPB in BC 9.0 2005 Bark Beetle Outbreak in British Columbia 8.0 2004 7.0 6.0 5.0 2003 4.0 3.0 2.0 2002 1.0 2001 2000 1999 0 1910 1930 1950 1970 1990 2010 Year (Figure courtesy Allen Carroll) Wide-Spread Glacial Retreat has Accompanied 20th Century Warming. 1902 2002 The recession of the Illecillewaet Glacier at Rogers Pass between 1902 and 2002. Photographs courtesy of the Whyte Museum of the Canadian Rockies & Dr. Henry Vaux. Loss of glacial mass may increase summer flow in the short term and decrease summer flow in the long term. Warming Air Temperatures will Increase Water Temperature Mantua, N., I. Tohver, A.F. Hamlet, 2009: Impacts of climate change on key aspects of freshwater salmon habitat in Washington State, (in review) Adaptation Approaches to Adaptation and Planning •Anticipate changes. Accept that the future climate will be substantially different than the past. •Use scenario based planning to evaluate options rather than the historic record. •Expect surprises and plan for flexibility and robustness in the face of uncertain changes rather than counting on one approach. •Plan for the long haul. Where possible, make adaptive responses and agreements “self tending” to avoid repetitive costs of intervention as impacts increase over time.