The Role of Cold Season Processes On Soil Erosion in the Great Lakes Region.

The effect of cold season processes on soil erosion is becoming increasingly important for sustainable management of soil resources, especially in regions where agricultural land use is dominant.  The recently developed VIC-WEPP model integrates the macro scale Variable Infiltration Capacity (VIC) hydrological model with the process-based Water Erosion Prediction Project (WEPP) model.  The coupled model can estimate soil loss for multi-state regions and river basins. This paper quantifies the impact of cold season processes including snow melt and soil freeze-thaw on soil erosion in three states in the Great Lakes region: Michigan, Minnesota, and Wisconsin. The coupled model was calibrated and evaluated for cold season erosion processes using runoff, frost depth, snow depth, and sediment data from the Palouse Conservation Field Station near Pullman, Washington, collected between 1984 and 1990. Soil frost’s quantified effects on runoff, soil moisture and erosion were studied through the application of the Coupled model in two small watersheds with and without having the representation of soil frost accounted for. Before scaling up to the full three state domains with the coupled model, comparisons were conducted to soil loss simulated by the coupled model with estimations of the full WEPP model. Finally the coupled VIC-WEPP model was applied to the three state domains to study the effects of soil freeze – thaw process on soil erosion and on trends of soil erosion related to the cold season process over 51 year period from 1949 to 2000 taking spatial and temporal variability of cold season processes into consideration. Using static land use based on modern conditions and observed climatic dataset, soil loss, soil erodibility within the three states was studied during extreme climatic years, like cold-wet, dry-warm which have a strong impact on soil frost depth.