Snow cover serves as an insulation layer, so changes in frost depth are slower under thicker snow packs. Therefore the better simulations of snow cover will yield better simulations of frozen soils. Due to the size of the Upper Mississippi it was broken into five subbasins to help with the calibration. A. Sub-Basin Calibration Runs Figure 9 shows weekly outflow from the gauged catchments of the Illinois the Minnesota, and the Mississippi above Anoka. These subbasins were selected for further analysis because they have the best calibrations at this time.
Black lines indicate observations, red dashed line indicate simulations.
Simulations run without frozen soil model. Baseflow from the frozen soil model is lower during the winter, since less of the mid-winter melt infiltrates. During spring melt the frozen soil model produces narrower peaks, since more of the melt water runs off directly and does not contribute much to baseflow. The frozen soil model has less of an effect in the Illinois since that basin is warmer and receives less snow. Simulated outflow for three of the calibration subbasins.