October 28, 2003
Mid-term reservoir storage forecasts and their use in water resource management
Mid-term water forecasts (two weeks to six months) are extremely important in the management of municipal water supplies. These forecasts include forecasts of water demands, future inflows, water management options, and required instream fish flows. Several of these forecasts are significantly impacted by future temperature and rainfall conditions. Although many approaches could be used to generate forecasts, two common approaches use: 1) past historic conditions to forecast the future (sometimes termed Ensemble Streamflow Prediction) and 2) the future weather conditions based upon forecasted weather (such as those generated by that National Centers for Environmental Prediction).
This presentation reviews the steps required to generate six-month predictions of reservoir storage and streamflow for the Puget Sound area. The approach used to generate water demands and streamflows is described. The sensitivity of future storage to operating policy and instream flow requirements is also determined. Measures of the forecast quality of NCEP predictions are also compared to those using the ESP approach.