Research

Hydrology and Water Resources: Current Research

Extending Mid-Range Forecasts for Puget Sound Municipal Water Supplies

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Background

The ability to forecast seasonal water supplies at lead times exceeding those of traditional weather forecasts (7- to 10 days) can provide a major benefit to resource managers faced with multiple and often competing water supply requirements. Mid-range forecasts may, for example, help resource managers fine-tune seasonal water allocations between environmental instream flows, irrigation supplies, and recreational activities. Mid-range forecasts may also provide critical (but not deterministic) information regarding the potential duration of droughts.

Research Objectives

The purpose of this research is to develop mid-range (up to 6 month) forecasts for water resource management. The geographical area used for these forecasts is the Puget Sound region of the Pacific Northwest .

The project incorporates 6-month climate signals developed by the National Centers for Environmental Prediction (NCEP) to drive a hydrologic model to produce monthly streamflow forecasts in the Puget Sound region. The meteorological forecasts produced by NCEP consist of 20 projections (ensembles) of monthly total precipitation and average temperature for the proceeding 6 months. These forecasts are bias-corrected, downscaled and disaggregated to force a hydrologic model for developing mid-range seasonal forecasts. Forecasted metrics include:

The development of monthly forecasts began in January, 2003 (Figure 1). Future research in this area will include developing methods to quantify the ensemble forecasts in an effort to develop finer projections of future water supply conditions. The value of the streamflow forecasts as a useful water management tool will also be assessed.

click image to enlarge

September 2003 streamflow forecast (forecasting from October 2003 through March 2004) for the Cedar River as it discharges into Chester Morse Reservoir

Figure 1 Experimental September 2003 streamflow forecast for the Cedar River as it discharges into Chester Morse Reservoir. This experimental forecast (forecasting from October 2003 through March 2004) indicates below normal flows for October 2003, above average flows for November 2003, below average flows flows for December 2003 and January 2004, then near normal flows for February and March.

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