Climate Change in the Pacific Northwest and Implications for the Snake River Basin JISAO Climate Impacts Group and the Department of Civil Engineering University of Washington September, 2001 Alan F. Hamlet Andy Wood Dennis P. Lettenmaier

(mm) Winter Precipitation Summer Precipitation

Hydrologic Characteristics of PNW Rivers

Sensitivity of Snowmelt and Transient Rivers to Changes in Temperature and Precipitation Temperature warms, precipitation unaltered: Streamflow timing is altered Annual volume stays about the same Precipitation increases, temperature unaltered: Streamflow timing stays about the same Annual volume is altered

Effect of 1992 Winter Climate on Two PNW Rivers Cedar River Western Cascades (caused predominantly by warm temperatures) Columbia River at The Dalles (caused both by warm temperatures and decreased precipitation)

Changes in Mean Temperature and Precipitation from GCMs ColSim Reservoir Model VIC Hydrology Model

Climate Change Scenarios 2020s

Climate Change Scenarios 2040s

The main impact: less snow April 1 Columbia Basin Snow Extent

Columbia River at The Dalles 2020s “Middle-of-the-Road” Scenario

Columbia River at The Dalles 2040s “Middle-of-the-Road” Scenario

Water Resources in the Columbia River Basin System objectives affected by winter flows Winter hydropower production (PNW demand) System objectives affected by summer flows Flood control Summer hydropower production (California demand) Irrigation Instream flow for fish Recreation

Simulated Reliability of Water Resources Objectives for “Middle-of-the-Road” Scenarios

1 Palisades 2 Milner 3 Oxbow 4 Ice Harbor 5 Kiona 5 4 3 1 2

Snake River at Palisades

Snake River at Milner

Snake River at Oxbow

Snake River at Ice Harbor

Climate Change Implications for the Snake River Basin Considered in isolation, the upper basin is probably well protected against relatively small temperature related streamflow timing shifts, but is vulnerable to uncertain reductions in precipitation, and basinwide considerations. Irrigation and summer streamflows in the lower basin are vulnerable to temperature related streamflow timing shifts and potential reductions in precipitation. Upper basin storage and irrigation demand may be indirectly affected by expected reductions in summer streamflows in the lower basin and main stem of the Columbia, since limited reservoir storage in the lower basin (Dworshak) is available to maintain streamflows in the lower basin (e.g. at Lower Granite). Maintaining water temperature at acceptable levels may also pose considerable challenges.