Winter Hydrologic and Erosion Processes in the U.S. Palouse Region: Field Experimentation and WEPP Simulation

Soil erosion by water is detrimental to soil ferƟ lity, crop yield, and the environment. For cold areas, knowledge of winter hydrologic processes is criƟ cal to determining land-use and management pracƟ ces for reducing soil loss and protecting land and water resources. Adequate understanding of winter processes is also essenƟ al to developing models as eff ecƟ ve predicƟ ve tools. This study evaluated the eff ects of two contrasƟ ng Ɵ llage pracƟ ces on winter hydrologic and erosion processes, and the suitability of the Water Erosion PredicƟ on Project (WEPP) model with a newly implemented energy-budget-based winter rouƟ ne for quanƟ fying these processes. Research plots subject to two Ɵ llage treatments— conƟ nuous Ɵ lled bare fallow (CTBF) and no-Ɵ ll (NT) seeding of winter wheat (Tri�u cum aes�u vum L. cv. Madsen) aŌ er spring barley (Hordeum vulgare L.)—were established at the USDA-ARS Palouse ConservaƟ on Field StaƟ on, Pullman, WA. The plots were monitored for runoff , erosion, soil temperature, water content, and depths of snow and freeze– thaw during October to May of 2003–2004 through 2006–2007. The NT plot generated negligible runoff and erosion (0.5 mm, 0.2 Mg ha −1 ) compared with CTBF (323 mm, 547 Mg ha −1 ). Frost occurred more frequently and was deeper in CTBF, probably due to its lack of residue and shallower snow depth. The modifi ed WEPP model could reasonably reproduce major winter processes, yet it cannot represent all the complicated winter phenomena observed in the fi eld. ConƟ nued eff orts are needed to further improve the ability of WEPP to properly account for soil freeze–thaw and thus transient soil hydraulic properƟ es and hydrologic and erosion processes.