IMPROVING FROST-SIMULATION SUBROUTINES OF THE WATER EROSION PREDICTION PROJECT (WEPP) MODEL.

Erosion models play an important role in assessing the influence of human activities on the environment. For cold areas, adequate frost simulation is crucial for predicting surface runoff and water erosion. The Water Erosion Prediction Project (WEPP) model is a physically based erosion prediction software program developed by the USDA. One of the major components of WEPP is the simulation of winter processes, which include snow accumulation and melt as well as soil freeze and thaw. WEPP is successfully used in the evaluation of important natural resource issues throughout the U.S. and in a number of other countries. However, previous studies revealed problems in the winter component of the WEPP model, especially the routine for frost simulation. The main purpose of this study was to improve the WEPP model (v2006.5) by changing the soil profile discretization and computation of key thermal and hydraulic parameters in the frost simulation routines so that the model can adequately simulate soil freeze-thaw and winter runoff and erosion. WEPP v2006.5 and the modified version (v2010.1) were applied to experimental plots in Pullman, Washington, and Morris, Minnesota. The simulated snow and frost depths as well as runoff and sediment yield were contrasted and compared with field observations, the results from v2010.1 showed substantial improvement compared to those from v2006.5. [ABSTRACT FROM AUTHOR]