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ARS Home » Pacific West Area » Pullman, Washington » Northwest Sustainable Agroecosystems Research » Research » Publications at this Location » Publication #189230
Title: SPAW AND WEPP SIMULATIONS OF OBSERVED SNOW ACCUMULATION AND MELT

Author
item ANDERSON, T - UNIVERSITY OF IDAHO
item McCool, Donald

Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 9/2/2005
Publication Date: 12/2/2005
Citation: Anderson, T., McCool, D.K. 2005. SPAW and WEPP Simulations of Observed Snow Accumulation and Melt. ASAE Pacific Northwest Section Meeting. September 22-24, 2005, Lethbridge, Alberta, Canada. Paper No. PNW05-1016. Available: http://asae.frymulti.com/request.asp?search=1&JID=8&AID=20056&CID=smppnr&v=&i=&T=1

Interpretive Summary: Snow melt erosion in the Revised Universal Soil Loss Equation Version 2 (RUSLE2) is sometimes estimated using empirical relationships developed from erosion and climate data collected in freeze/thaw dominated areas of the Inland Pacific Northwest. However, improved techniques are needed to estimate snow accumulation and melt and resulting erosion on snow melt dominated cropland in western states and other areas of the US. Two models, SPAW and WEPP, were tested for ability to model snow accumulation and melt events. Daily climate data collected over a 30-year period from four weather stations in cold cropland areas of the western US was used in SPAW and WEPP to simulate snow accumulation and melt. SPAW routine is based on average air temperature, with accumulation occurring at 32 and melt at 33 degrees F. Simulated snow depths were generally less than observed and snow pack was predicted to melt before observed. Adjusting accumulation and melt temperatures improved the match with observed data. WEPP routine is based on maximum air temperature, with accumulation occurring at 0 degrees C, and melt occurring at -2.8 degrees C when other conditions are met. Simulated snow depths also tended to be less than observed, and like SPAW, melted more rapidly than observed. Both SPAW and WEPP missed important snowfall events, usually when the daily minimum air temperature was just below freezing. A modified WEPP routine based on minimum air temperature captured these missing events, estimated snow depths closer to observed, and prolonged the time of snow cover better than WEPP. SPAW with adjusted parameters was the best of these models for estimating snow accumulation and melt on high elevation non-irrigated cropland of the western US and to provide input databases for RUSLE2.

Technical Abstract: Snow melt erosion in the Revised Universal Soil Loss Equation Version 2 (RUSLE2) is estimated using empirical relationships developed from erosion and climate data collected in freeze/thaw dominated areas of the Pacific Northwest. Improved techniques are needed to estimate snow accumulation and melt and resulting erosion on snow melt dominated cropland in western states and other areas of the US. The SPAW and WEPP models were tested for ability to model snow accumulation and melt events. Daily climate data collected over a 30-year period from four weather stations in cold cropland areas of the western US was used in SPAW and WEPP to accumulate and melt snow. The SPAW routine is based on average air temperature, with accumulation occurring at 32 and melt at 33 degrees F. Simulated snow depths were generally less than observed and snow pack was predicted to melt before observed records indicate. Adjusting accumulation and melt temperatures improved the match with observed data. The WEPP routine is based on maximum air temperature, with accumulation occurring at 0 degrees C, and melt occurring at -2.8 degrees C when other conditions are met. Simulated snow depths also tended to be less than observed, and like SPAW, melted away quicker than observed data indicate. Both SPAW and WEPP missed important snowfall events, usually when the daily minimum air temperature was just below freezing. Simulations using a modified WEPP winter routine based on minimum air temperature captured these missing events, estimated snow depths closer to observed, and prolonged the time of snow cover better than did WEPP. SPAW with adjusted temperature parameters was the best of these models for estimating snow accumulation and melt on high elevation non-irrigated cropland of the western US and to provide input databases for RUSLE2.