Alan F. Hamlet, Philip W. Mote, Dennis P. Lettenmaier JISAO/CSES Climate Impacts Group Dept. of Civil and Environmental Engineering University of Washington Understanding the Effects of Climate Change on Water Resources in the Pacific Northwest

Image Credit: National Snow and Ice Data Center, W. O. Field, B. F. Molnia Aug, 13, 1941Aug, 31, 2004 Recession of the Muir Glacier

Tmin Tmax PNW CA CRB GB Canada USA

Mote P.W.,Hamlet A.F., Clark M.P., Lettenmaier D.P., 2005, Declining mountain snowpack in western North America, BAMS, 86 (1): Trends in April 1 SWE

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):

Projections for the Future Using Global Climate Models

Natural Climate InfluenceHuman Climate Influence All Climate Influences Natural AND human influences explain the observations of global warming best.

Pacific Northwest °C °C °C °C Observed 20th century variability +1.7°C +0.7°C +3.2°C

Pacific Northwest % -1 to +3% -1 to +9% -2 to +21% Observed 20th century variability +1% +2% +6%

Hydroclimatology of the Pacific Northwest

Annual PNW Precipitation (mm) Elevation (m) Winter climate in the mountains is the key driver of streamflow. Snowpack functions as a natural reservoir.

Hydrologic Characteristics of PNW Rivers

Effects of the PDO and ENSO on Columbia River Summer Streamflows Cool Warm high low PDO

Temperature warms, precipitation unaltered: Streamflow timing is altered Annual volume may be somewhat lower due to increased ET Black: Obs Red: 2.3° C warming Warming Affects Streamflow Timing

Precipitation increases, temperature unaltered: Streamflow timing stays about the same Annual volume is altered Black -- Obs Blue -- 9% increase in precip. Precipitation Affects Streamflow Volume

Hydrologic Impacts for the PNW

Snow Model Schematic of VIC Hydrologic Model and Energy Balance Snow Model PNW 1/16 th Deg. 6 km

The warmest locations that accumulate snowpack are most sensitive to warming +2.3C, +6.8% winter precip

Simulated Changes in Natural Runoff Timing in the Naches River Basin Associated with 2 C Warming Increased winter flow Earlier and reduced peak flows Reduced summer flow volume Reduced late summer low flow

Chehalis River Rain Dominant

Hoh River Warm Transient Snow

Nooksack River Cooler Transient Snow

Skagit River Snowmelt Dominant

April 1 SWE (mm) 20 th Century Climate“2040s” (+1.7 C)“2060s” ( C) -3.6%-11.5% Changes in Simulated April 1 Snowpack for the Canadian and U.S. portions of the Columbia River basin (% change relative to current climate) -21.4%-34.8%

Effects of Basin Winter Temperatures Northern Location (colder winter temperatures) Southern Location (warmer winter temperatures)

Decadal Climate Variability and Climate Change

Will Global Warming be “Warm and Wet” or “Warm and Dry”? Answer: Probably BOTH!

Regionally Averaged Cool Season Precipitation Anomalies PRECIP

Impacts to the Columbia River Hydro System

Impacts on Columbia Basin hydropower supplies Winter and Spring: increased generation Summer: decreased generation Annual: total production will depend primarily on annual precipitation (+2C, +6%) (+2.3C, +5%) (+2.9C, -4%) NWPCC (2005)

Warming climate impacts on electricity demand NWPCC 2005 Reductions in winter heating demand Small increases in summer air conditioning demand in the warmest parts of the region

Source: Payne, J.T., A.W. Wood, A.F. Hamlet, R.N. Palmer and D.P. Lettenmaier, 2004, Mitigating the effects of climate change on the water resources of the Columbia River basin, Climatic Change Vol. 62, Issue 1-3, Climate change adaptation may involve complex tradeoffs between competing system objectives

Instream Flow Augmentation and Water Quality

Simulated Changes in Natural Runoff Timing in the Naches River Basin Associated with 2 C Warming Increased winter flow Earlier and reduced peak flows Reduced summer flow volume Reduced late summer low flow

Temperature thresholds for coldwater fish in freshwater +1.7 °C +2.3 °C Warming temperatures will increasingly stress coldwater fish in the warmest parts of our region –A monthly average air temperature of 68ºF (20ºC) has been used as an upper limit for resident cold water fish habitat, and is known to stress Pacific salmon during periods of freshwater migration, spawning, and rearing

Overview of Some Water Resources Impact Pathways

Water Supply and Demand Changes in the seasonality water supply (e.g. reductions in summer) Changes in water demand (e.g. increasing evaporation) Changes in drought stress Increasing conflicts between water supply and other uses and users of water Energy Supply and Demand Changes in the seasonality and quantity of hydropower resources Changes in energy demand Increasing conflicts between hydro and other uses and users of water Instream Flow Augmentation Changes in low flow risks Changes in the need for releases from storage to reproduce existing streamflow regime. Changes in water resources management related to water quality (e.g. to provide dilution flow or to control temperature)

Flood Control and Land Use Planning Changes in flood risks Changes in flood control evacuation and timing Dam safety Impacts in Estuaries Impacts of sea level rise and changing flood risk on low lying areas (dikes and levies) Impacts to ecosystem function Changes in land use policy (coastal armoring, land ownership, FEMA maps) Long-Term Planning, Water Resources Agreements, Water Law and Policy Water allocation agreements in a non-stationary climate (e.g. water permitting) Appropriateness of the historic streamflow record as a legal definition of climate variability Need for new planning frameworks in a non-stationary climate Transboundary implications for the Columbia Basin

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. Approaches to Adaptation and Planning

Overview of Some Existing Climate Change Water Planning Studies Seattle Water Supply (Wiley 2004) White River Basin (Ball 2004) Snohomish Basin (Battin et al. 2007) Columbia Hydro System (Hamlet et al. 1999; Payne et al. 2004, NWPCC 2005) Ball, J. A Impacts of climate change on the proposed Lake Tapps-White River water supply, M.S.C.E. thesis, Dept. of Civil and Environmental Engineering, College of Engineering, University of Washington, Seattle. Battin J., Wiley, M.W., Ruckelshaus, M.H., Palmer, R.N., Korb, E., Bartz, K.K., Imaki, H., Projected impacts of climate change on salmon habitat restoration, Proceedings of the National Academy of Sciences of the United States of America, 104 (16): Hamlet, A. F. and D. P. Lettenmaier. 1999b. Effects of climate change on hydrology and water resources in the Columbia River Basin. Journal of the American Water Resources Association 35(6): Payne, J. T., A. W. Wood, A. F. Hamlet, R. N. Palmer, and D. P. Lettenmaier Mitigating the effects of climate change on the water resources of the Columbia River basin. Climatic Change 62: NW Power and Conservation Council, 2007, Effects of Climate Change on the Hydroelectric System, Appendix N to the NWPCC Fifth Power Plan, Wiley, M. W Analysis techniques to incorporate climate change information into Seattle's long range water supply planning. M.S.C.E. thesis, Dept. of Civil and Environmental Engineering, College of Engineering, University of Washington, Seattle.