Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 8/31/2007
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: The unique winter climate of the Northwestern Wheat and Range Region (NWRR) of the Pacific Northwest USA creates a challenge for modeling snow accumulation and melt and interaction with soil freezing and thawing. The climate has sometimes been described as Mediterranean with 55 to 65 % of the annual precipitation occurring between November and April. Mean temperature at Pullman, Washington is -2 °C in December and -1 °C in January, the two coldest months. The mixed winter rain and snow season, and intermittent freeze and thaw of soils are not well approximated by simple temperature-driven winter hydrology models. During thawing periods, soil strength is reduced and storm events can easily detach and transport the soil. Steep slopes combined with continued use of aggressive tillage practices can lead to severe erosion. To better understand the winter hydrologic and erosion processes in the Pacific Northwest (PNW), a combination of field experimentation and mathematical modeling was implemented. The specific objectives of our study were to evaluate (i) the effect of two widely different managements, continuous tilled fallow and no-till seeded winter wheat, on snowmelt, soil freeze and thaw, and runoff and erosion processes, and (ii) the performance of the USDA’s WEPP (Water Erosion Prediction Project) model with energy-based winter routines in predicting erosion and hydrologic processes. WEPP model was run for the time period of 2003–2006. Snow depth, soil freeze and thaw depths, surface runoff and sediment were collected for three paired field plots under continuous tilled fallow and no-till seeded winter wheat. For two selected plots, soil moisture and temperature were continuously monitored at several depths. Suitability and performance of the modified WEPP model was assessed. The WEPP model with energy-based winter routines could reasonably reproduce the snow, frost and thaw depths, and runoff.