Incorporating weather and climate predictions from NCEP GFS and CFS into seasonal water supply forecasts for the Colorado River basin

Predictions spring and summer runoff volumes -- termed “water supply forecasts” -- are issued throughout each water year to help water and energy managers allocate resources or operate reservoir systems efficiently. In recent years, the National Weather Service (NWS) Colorado Basin River Forecast Center (RFC) has augmented its traditional statistical methods for water supply forecasting by implementing operational model-based Ensemble Streamflow Prediction (ESP) forecasts, which are now made on a weekly basis. ESP forecasts have typically incorporated an ensemble of observed weather sequences – i.e., representing future climate with a climatological ensemble. The NWS Office of Hydrologic Development (OHD) has developed a new approach for integrating both weather forecasts from a frozen prior version of the current NCEP GFS model for which ensemble reforecasts are available, and climate forecasts from the current NCEP CFS model, into the ESP method. Using a series of hindcasts spanning several decades, we compared streamflow forecasts produced via the new approach with those from climatological ESP, for a set of test catchments in the Colorado River basin. This presentation reports on the results of the evaluation.