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Understanding the Effects of Climate Change and Climate Variability on the Water Cycle in the Pacific Northwest Alan F. Hamlet, Philip W. Mote, Dennis P. Lettenmaier •JISAO/CSES Climate Impacts Group •Dept. of Civil and Environmental Engineering University of Washington Observed 20th century variability °C +3.2°C +1.7°C +0.7°C 0.9-2.4°C 0.4-1.0°C Pacific Northwest 1.2-5.5°C Observed 20th century variability % -1 to +3% +1% +6% +2% -1 to +9% Pacific Northwest -2 to +21% Local changes in climate may be larger than regional changes, but are also inherently more uncertain, particularly for precipitation. Projected Hydrologic Changes Associated with Warming For areas that accumulate substantial snowpack, the areas close to freezing in mid-winter are most sensitive to warming. ~2060 +2.3C, +4.5% winter precip Changes in Simulated April 1 Snowpack for the Canadian and U.S. portions of the Columbia River basin (% change relative to current climate) 20th Century Climate “2040s” (+1.7 C) -3.6% -21.4% April 1 SWE (mm) “2060s” (+ 2.25 C) -11.5% -34.8% 20th 600 Area Average Water (depth in mm) Seasonal Water Balance Naches River 700 500 precipitation 400 swe runoff+baseflow soil storage 300 evapotranspiration 200 100 Century Climate sep aug jul jun may apr mar feb jan dec nov oct 0 700 precipitation 400 swe runoff+baseflow soil storage 300 evapotranspiration 200 100 sep aug jul jun may apr mar feb jan dec 0 nov + 2.25° C + 4% precip 500 oct Mid 21st Century Scenario Area Average Water (depth in mm) 600 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 Simulated Changes in Natural Runoff Timing in the BC Portion of the Columbia River Basin Associated with 2 C Warming Basin Average Runoff (mm) 180 160 140 120 100 Runoff base Runoff plus2C 80 60 40 20 0 oct nov dec jan feb mar apr may jun jul aug sep 1987 1987 1986 1986 1986 1986 1985 1985 1985 1985 1984 1984 1984 1984 250 1987 1987 1986 1986 1986 1986 1985 1985 1985 1985 1984 1984 1984 1984 1983 1983 1983 1983 1982 1982 1982 1982 1981 1981 1981 1981 1980 Simulated Snow Accumulation (mm) 450 1983 1983 1983 1983 1982 1982 1982 1982 1981 1981 1981 1981 1980 Simulated Snow Accumulation (mm) 500 Revelstoke Area (1268m) 400 350 300 1915 250 2003 200 plus2C 150 100 50 0 300 Revelstoke Area (473m) 200 1915 150 2003 plus2C 100 50 0 1987 1987 1986 1986 1986 1986 1985 1985 1985 1985 1984 600 1984 1987 1987 1986 1986 1986 1986 1985 1985 1985 1985 1984 1984 1984 1984 1983 1983 1983 1983 1982 1982 1982 1982 1981 1981 1981 1981 1980 Simulated Snow Accumulation (mm) 700 1984 1984 1983 1983 1983 1983 1982 1982 1982 1982 1981 1981 1981 1981 1980 Simulated Snow Accumulation (mm) 800 Golden Area (1376m) 600 500 1915 400 2003 300 plus2C 200 100 0 700 Golden Area (827m) 500 400 1915 2003 300 plus2C 200 100 0 Is it really happening? Regional Scale Trends in Temperature for the Western U.S. and B.C. Columbia Basin Linear Trend (Deg. C per century) 4.00 CA CRB GBAS 3.00 PNW PNWBC 2.00 1.00 0.00 oct nov dec jan feb mar apr may jun jul aug sep -1.00 -2.00 Linear Trend (Deg. C per century) 5.00 CA CRB 4.50 GBAS 4.00 PNW PNWBC 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00 oct nov dec jan feb mar apr may jun jul aug sep 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 As the West warms, spring flows rise and summer flows drop Stewart IT, Cayan DR, Dettinger MD, 2005: Changes toward earlier streamflow timing across western North America, J. Climate, 18 (8): 1136-1155 Wide-Spread Glacial Retreat has Accompanied 20th Century Warming. Loss of glacial mass may increase summer flow in the short term and decrease summer flow in the long term. 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. Water Supply Impact Pathways Reductions in Supply Climate Change Increases in Demand Increasing Population Conflicts with Other Water Resources Objectives Combined Impacts In sensitive areas, systematic reductions in summer water availability will decrease the yield of water supply systems. Master's Thesis: Wiley, M.W. (2004). "Analysis Techniques to Incorporate Climate Change Information into Seattle’s Long Range Water Supply Planning," University of Washington Impact Pathways Associated with Hydrologic Changes Changes in water quantity and timing Reductions in summer flow and water supply Increases in drought frequency and severity Changes in extremes Changing flood risk (up or down) Summer low flows Changes in groundwater Changes in water quality Increasing water temperature Changes in sediment loading (up or down) Changes in nutrient loadings (up or down) Changes in vegetation Forest fire Insects Disease Invasive species Changes in outdoor recreation Skiing Camping Boating