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ARS Home » Pacific West Area » Pullman, Washington » Northwest Sustainable Agroecosystems Research » Research » Publications at this Location » Publication #197967

Title: SUCCESS OF SPAW AND WEPP IN SIMULATING ACCUMULATION AND MELT OF SNOW.

Author
item Mccool, Donald
item Anderson, Todd
item Walter, M
item Williams, John

Submitted to: International Symposium on Soil Erosion and Dryland Farming
Publication Type: Proceedings
Publication Acceptance Date: 5/12/2006
Publication Date: N/A
Citation: N/A

Interpretive Summary: Lack of a method to account for snowmelt runoff and erosion in the Revised Universal Soil Loss Equation Version 2 (RUSLE2) hampers use of this popular erosion model in areas where there is a period of melting of snow accumulated during the winter. We tested the SPAW and WEPP models for their ability to provide snow accumulation and melt data from which we could develop erosivity databases for RUSLE2. Initial tests were based on daily climate data collected over a thirty-year period from four weather stations in cold or high elevation cropland areas of the western U.S. and was then expanded to include climate data from areas in the northern Great Plains. Snow depths predicted with SPAW were generally less than observed and the snow pack was predicted to melt before observed. Adjusting the accumulation and melt temperatures in SPAW allowed for a much better match to the observed data. The default routine in WEPP is based on maximum daily air temperature, with accumulation occurring when temperatures are at 0 degrees Celsius or below, and melt occurring when temperatures are above -2.8 degrees Celsius and other conditions are met. Simulated snow depths with WEPP also tended to be less than observed, and like SPAW, snow melted more quickly than the historical data indicated. Both SPAW and WEPP missed significant snowfall events in their simulations, usually when the daily minimum air temperature was just below freezing. Because of the ease of adjusting accumulation and melt temperatures in SPAW, and some idiosyncrasies of WEPP, better results were obtained with SPAW. The SPAW model can be used to estimate snow accumulation and melt, and develop winter erosivity databases for RUSLE2. This will enable the use of RUSLE2 in areas with snowmelt erosion.

Technical Abstract: Lack of a method to properly account for snowmelt runoff and erosion in the Revised Universal Soil Loss Equation Version 2 (RUSLE2) hampers use of the model in areas where there is a period of melting of snow accumulated during the winter. We tested the SPAW and WEPP models for ability to provide snow accumulation and melt data we could use to develop the erosivity databases needed by RUSLE2. Initial tests were based on daily climate data collected over a thirty-year period from four weather stations in cold or high elevation cropland areas of the western U.S. and was then expanded to include climate data from areas in the northern Great Plains. Snow depths predicted with SPAW were generally less than observed values and the snow pack was predicted to melt before observed records indicated. Adjusting the accumulation and melt temperatures in SPAW allowed for a much better match to the observed data. The default routine in WEPP is based on maximum daily air temperature, with accumulation occurring when temperatures are at 0 degrees Celsius or below, and melt occurring when temperatures are above -2.8 degrees Celsius and other conditions are met. Simulated snow depths with WEPP also tended to be less than the observed depths, and like SPAW, snow melted more quickly than the historical data indicated. Both SPAW and WEPP missed significant snowfall events in their simulations, usually when the daily minimum air temperature was just below freezing. Because of the ease of adjusting accumulation and melt temperatures in SPAW, and some idiosyncrasies of WEPP, better results were obtained with SPAW. The SPAW model can be used to estimate snow accumulation and melt and develop winter erosivity databases for RUSLE, enabling its use in areas with snowmelt erosion.