Satellite Snowcover Perspective on the Drought: Colorado and Rio Grande Basins

Estimating snowcover properties at a basin scale, particularly snow water equivalent (SWE), remains a challenge. We have used a combination of remote sensing and ground-based data to estimate snow covered area (SCA) and SWE for portions of the Southwestern U.S. for an eight-year period, 1995-2002. Two immediate applications for this product were to: i) evaluate the seasonal and interannual variability in snowcover patterns, and ii) provide snowpack information for evaluating hydrologic models of snowmelt runoff and other components of the water balance. Fractional snow covered area (SCA) maps with a 1-km2 grid were developed from AVHRR scenes using a three-part cloud masking procedure and spectral unmixing algorithm. A 1-km2 SWE product was developed for the same area using interpolation of ground-based SNOTEL data, followed by masking with the SCA scenes. The fractional SCA product showed areas with persistent snowcover to be relatively reproducible from year to year, corresponding to higher elevations. However, there were different January through June patterns of snowcover persistence during recent drought years as compared to previous years. The annual maximum snow extent, or area with any snowcover during the year, exhibited significant interannual variability, and was not well correlated with maximum SWE. The current products are available on a set of CD's (see http://resac.hwr.arizona.edu). Abstract only.