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Climate impacts on the Pacific Northwest environment: Hydrology and water resources Dennis P. Lettenmaier Department of Civil and Environmental Engineering and Climate Impacts Group University of Washington Characteristics of the current PNW climate Annual PNW Precipitation (mm) Hydrologic Characteristics of PNW Rivers Normalized Streamflow 3.0 2.5 Snow Dominated 2.0 Transient Snow 1.5 Rain Dominated 1.0 0.5 0.0 10 11 12 1 2 3 4 Month 5 6 7 8 9 A history of the PDO A history of ENSO warm warm cool 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Columbia River Apr-Sep streamflow 105 cubic feet per second 5 4 3 2 1 0 1900 1920 1940 1960 1980 2000 Sensitivity of Snow-dominated and Transient Rivers to Changes in Temperature and Precipitation 900000 700000 600000 500000 400000 300000 200000 100000 1974 1974 1974 1974 1974 1974 1974 1974 1974 1974 1973 1973 1973 1973 1973 0 1973 •Streamflow timing is altered • Annual volume stays about the same 800000 Flow (cfs) Temperature warms, precipitation unaltered: Water Year 900000 800000 600000 500000 400000 300000 200000 100000 1974 1974 1973 1973 1973 1973 1973 0 1973 •Streamflow timing stays about the same •Annual volume is altered 700000 Flow (cfs) Precipitation increases, temperature unaltered: Water Year 800000 Forecast1 700000 Forecast2 600000 Forecast3 500000 Forecast4 400000 Forecast5 Forecast6 300000 Forecast7 200000 Forecast8 100000 High Climatology Month sep aug jul jun may apr mar feb jan dec nov 0 oct Streamflow (cfs) 1998 cool PDO/warm ENSO Low Climatology Observed Virgin Flow 800000 700000 Forecast1 1999 cool PDO/cool ENSO Forecast2 600000 Forecast4 Forecast5 500000 Forecast6 400000 Forecast7 300000 Forecast8 Forecast9 200000 Forecast10 100000 Forecast11 Forecast12 Month sep aug jul jun may apr mar feb jan dec nov 0 oct Streamflow (cfs) Forecast3 High Climatology Low Climatology Observed Virgin Flow Forecast1 800000 Forecast2 700000 Forecast3 600000 Forecast4 Forecast5 500000 Forecast6 400000 Forecast7 300000 Forecast8 200000 Sim Min 100000 Sim Max Observed Virgin Flow sep aug jul jun may apr mar feb jan dec nov 0 oct Streamflow (cfs) 2001 cool PDO/ENSO neutral Temperature trends in the PNW • US Historical Climate Network data • 113 stations with long records • Almost every station shows warming • Urbanization not a major source of warming Observed temperature trend Historic Analogues for the Effects of Climate Change Unusually Warm Year Ollalie Meadows (3700 ft elevation) WY 1992 Near Normal Precipitation Warm Temperatures ( + 3.5 F) normal precipitation normal snowpack Effect of 1992 Winter Climate on Two PNW Rivers 1200 1000 Flow (cfs) (caused predominantly by warm temperatures) 800 1992 600 avg 400 200 Sep Aug Jul Jun May Apr Mar Feb Dec Oct Jan 0 Nov Cedar River Western Cascades 600000 400000 1992 300000 avg 200000 100000 Sep Aug Jul Jun May Apr Mar Feb Jan Dec Nov 0 Oct (caused both by warm temperatures and decreased precipitation) 500000 Flow (cfs) Columbia River at The Dalles Climate change: Predictions for the next century 54 53 52 51 50 49 48 47 46 45 44 s 20 40 s 20 20 s 20 00 s 19 80 s 19 60 s 19 40 s 19 20 s warmest scenario average coolest scenario observed CGCM1 00 19 Degrees F Northwest warming Precipitation changes low mean high precipitation Apr-Sep Oct-Mar -4% 0% +4% +8% +9% +22% Estimated climate change from 20th c. to 2040s using 8 climate model scenarios. Climate models: The current climate Interpreting the hydrologic effects The main impact: less snow April 1 Columbia Basin Snow Extent Columbia Basin Average Snow Water Equivalent HadCM2 (Warm/Wet) and ECHAM4 (Warm/Dry) Scenarios Basin Average Snow Water Equivalent (mm) Snow Accumulation and Ablation 200 180 160 140 Base 120 HC 2025 100 MPI 2025 80 HC 2045 60 MPI 2045 40 20 0 oct nov dec jan feb mar apr may jun jul aug sep Conclusion: Both Warm/Wet and Warm/Dry scenarios result in reduced SWE Other sectors (forests, fish, …) Forests Vegetation carbon Vegetation modeling for 2070-2100 including effects of changes in •temperature •precipitation (seasonality?) •CO2 (uncertain) Longer, hotter summers likely to take a toll on Northwest forests even with CO2 fertilization Courtesy Ron Neilson, OSU and climate damage Floods Low summer streamflow, high temp ???? Estuary conditions: prey, predators, competitors Impacts of climate change on the PNW Highest confidence: Models: warmer; higher snow line •summer water supply, drought •demand for water •conflicts over water resources •winter streamflow increases in snowmelt-driven basins •coastal flooding, inundation •salmon freshwater survival energy production Are we prepared for a changing climate? Natural resource management presently assumes that Climate does not change But what if it does? Adaptation pathways Assess the problem, identify vulnerabilities Long-term planning for reduced summer water Incorporate strategies into water policy