Adjustment of Ensemble Streamflow Predictions for Upstream Water Use and Regulation

 

Effects of Water Use and Regulation

In watersheds with appreciable water use and regulation (including storage reservoirs, in-stream withdrawals, and/or inter-basin water transfers), the development of reliable ensemble streamflow predictions (ESP) at downstream locations requires characterization and incorporation of the expected streamflow alterations from natural conditions and their associated uncertainty.  Streamflow alterations can be incorporated if, as part of the ESP forecast generation process, water use and regulation activities are represented with sufficient accuracy.  This approach can be effective in watersheds where flow alterations occur due to large, main stem river projects and well documented water use activities, but it becomes impractical where flow alterations result from many small and/or medium scale storage projects and water use activities distributed throughout the watershed.  In the latter cases, comprehensive information on reservoir filling and depletion, water withdrawals and returns, and/or water transfers is both not readily available and subject to change from year to year, adding bias and uncertainty to the flow forecasts. This research project develops and demonstrates procedures to characterize the aggregate flow alteration biases and uncertainty in watersheds in the latter category and incorporate them in ensemble streamflow predictions at downstream points.

Project Scope and Activities

This research project develops and demonstrates a new method to characterize the aggregate flow alteration biases and associated uncertainty in watersheds with important but largely undocumented water use and regulation activities.

The approach includes procedures to (a) detect the presence of significant upstream regulation and water use influences; (b) correct the ensemble streamflow predictions and associated uncertainty for any biases during periods when upstream regulation and water use influences are detected; and (c) assess the forecast reliability improvements. Validation results are reported for three California watersheds. The forecast adjustment approach has been developed for operational use in routine forecast operations of the U.S. National Weather Service River Forecast Centers.   

Related Publications

1.    Georgakakos, A.P., H. Yao, and K.P. Georgakakos, “Upstream Regulation Effects on Ensemble Streamflow Prediction,” Journal of Hydrology, in press, 2014.

Acknowledgements

This project was funded by the Hydrologic Research Laboratory of the National Weather Service and was carried out jointly by the Hydrologic Research Center (HRC; California) and the Georgia Water Resources Institute (GWRI; Georgia) in collaboration with the NWS River Forecast Centers.