Columbia River Basin Long-Term Water Supply and Demand Forecast

The Project

In November 2011, the Office of Columbia River (OCR) will publish its five year update of the Water Supply and Demand Forecast (Forecast). A draft report will be released in September, with workshops held in the Tri-cities, Wenatchee, and Spokane, Sept. 7-9.

OCR contracted with Washington State University to study the out-of-stream piece of the Forecast and with the Washington Department of Fish and Wildlife to do the instream component. It will be the most comprehensive study of future demand ever produced in the state of Washington. It employs state-of-the-art technology and scientific research to identify where additional water supply is needed, now and in the future. The results will guide OCR in developing a water management plan to meet eastern Washington’s environmental and economic needs.

Scope

The Forecast evaluates supply and forecasts demand on three tiers: basin-wide (which includes seven states and British Columbia,) at the watershed (water resource inventory area or WRIA) level, and within a one-mile corridor along the Columbia River. The Forecast examines:

• Water demand for four sectors: agricultural, municipal, hydroelectric, and instream flows.
• Water supplies.
• Climate change impacts.
• Instream flows for eight critical fish basins in eastern Washington.

Forecast

Water supply modeling conducted for the Forecast predicts warmer, wetter winters, when water demand is low, and hotter, dryer summers, when demand peaks. By 2030, the model predicts an increase in average annual flow in the basin of 2%, but the timing of flows could change dramatically depending on location within the basin. For example, flows on the Columbia River at Bonneville Dam are expected to increase by up to 35% from November to May, but decrease by up to 9% from June to October.

The Forecast includes an “instream atlas,” created by WDFW for eight fish critical watersheds in Eastern Washington: The atlas incorporates maps and information on streamflow restoration priorities and stream-level information on fish life history stages. The atlas shows that recovery opportunities exist in all eight WRIAs to improve fisheries, and that adopted instream flows for many of these WRIAs are routinely not met. OCR will use these tools to ensure that new water supply projects it funds will benefit instream flow and protect fish habitats

Agriculture is the largest single user of water in eastern Washington. The combined influences of climate change, economic trends and population growth will result in an increase in the amount of water needed for agricultural irrigation.

The Forecast predicts that by 2030, diversions for cities and communities in Eastern Washington will increase by approximately 24 percent or an additional 109,000 acre-feet per year, based on expected population growths.

Hydropower use in Eastern Washington is expected to remain fairly stable (no significant growth) over the next 20 years, with increases in demand being met through conservation and power from other sources.

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