Snow Estimation—A GIS Application for Water Resources Forecasting

by Ann McManamon, Hydrologic Research Lab, Silver Spring, United States,
Gerald N. Day, Hydrologic Research Lab, Silver Spring, United States,
Thomas R. Carroll, Hydrologic Research Lab, Silver Spring, United States,

Document Type: Proceeding Paper

Part of: Engineering Hydrology


In the Western United States approximately 75 percent of the annual runoff results from snowmelt. Observations of the snow cover provide an important source of information for forecasting seasonal water supply months in advance. The National Weather Service River Forecast System (NWSRFS) snow model relies on estimates of mean areal precipitation and mean areal temperature to compute estimates of current snow cover conditions. Because of the difficulty in accurately estimating precipitation in the mountains, it is essential that snow water equivalent observations be used to update model simulated snow cover conditions to ensure that forecasts of future water supply are accurate. This paper describes a software system that interpolates point observations to produce gridded estimates of snow water equivalent. The system uses the GRASS Geographical Information System (GIS) to store, analyze, and display point, line and gridded data. The GIS permits the analysis of multiple data layers such as elevation, seasonal precipitation, and derived data layers, e.g. slope and aspect. The outputs of the system include gridded estimates of snow water equivalent, as well as estimates of the areal snow cover conditions needed by the snow accumulation and ablation model that is part of NWSRFS. Updating the simulated snow conditions has been demonstrated to provide significant improvements in streamflow forecasting in areas with significant snow cover.

Subject Headings: Water resources | Hydrologic models | Water supply | Model accuracy | Snow | Geographic information systems | Forecasting | Water supply systems | United States

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