GIS tool to cpmpare simulated and remotely sensed snow-cover observations

A GIS (geographic information system)-based Snow-Cover Comparison Tool (SCCT) is being developed for useby watershed modelers and other analysts to make comparisons between simulated and remotely sensed snow cover. In the past, watershed-model simulations have been calibrated almost entirely by comparison of simulated with observed streamflow variations. Watershed-model calibrations can be improved by verifying that snowpack distributions and conditions within the basin are simulated accurately, but this requires careful registration of observations to model land units. The SCCT facilitates these additional comparisons. NOAA' s satellite-based snow-cover images on 1,101 meter grid cells are compared here with simulations, on 100-meter grid cells, of snowpacks in the Merced, American, and Carson Rivers of the Sierra Nevada on selected dates. Statistical analyses of disagreements between observed and simulated snow cover show a strong dependence of model error on altitude. Comparison maps, produced by the SCCT, make the spatial distributions of these errors easy to visualize.