National weather service extended streamflow prediction

A new technique under development by various elements of the Office of Hydrolgy, National Weather Service, for providing water supply forecasts is described. The method, known as Extended Streamflow Prediction (ESP), provides probabilistic streamflow predictions during any user-designated time period for headwater catchments. The ESP model utilizes physically-based conceptual hydrologic models and long-term historical records of precipitation and temperature to simulate a set of possible streamflow regimes conditioned upon the current hydrologic conditions of the catchment. The set of regimes can be analyzed for the following properties: total volume, maximum mean daily flow, minumum mean daily flow, or average mean daily flow for the period of interest and probability distributions developed. Thus, streamflow can be related to a desired chance of occurrence during the period and forecasts for predicted streamflow properties at user-selected levels of probability can be provided for any time period in the future. Applications to test catchments and proposals for future development are presented.