Figure 6 shows the distribution of two of these parameters, percent sand and percent clay. D. Routing Network and Calibration Basins VIC solves each grid cell in the basin independently, the runoff and baseflow results are then input to an external routing model. This model uses a specified routing network to determine the discharge at the basin outlet, and at user defined locations within the basin. These discharge simulations can then be compared against records from gauging stations. The routing network for the Upper Mississippi is shown in Figure 7 .
Colored nodes indicate the locations of calibration subbasins.
Point Model Tests Point model tests of the frozen soil model were conducted using data collected at the University of Minnesota Rosemount Agriculture Experiment Station. Figure 8 compares the VIC simulation with observations for the winter of 1994-95. Point model comparison of model simulation versus observations for the Rosemount, MN field site. 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.