Relationship between MODIS-Derived Snow Cover and Snowmelt Timing in the Wind River Range, Wyoming, 2000 to 2010

Earlier onset of springtime weather including earlier snowmelt has been documented in the western United States over at least the last 50 years. Because the majority (more than 70 percent) of the water supply in the western U.S. comes from snowmelt, analysis of the declining spring snowpack has important implications for streamflow management. For this work, ten years of Moderate-Resolution Imaging Spectroradiometer (MODIS) snow-cover, cloud-gap-filled (CGF) snow-cover map products and 30 years of stream discharge and meteorological station data are studied of the Wind River Range (WRR), Wyoming. Streamflow data from five streams in the WRR drainage basins show lower annual discharge and earlier snowmelt in the decade of the 2000s than in the previous three decades, though no trend of either lower streamflow or earlier snowmelt was observed within the decade of the 2000s. Results show a statistically-significant trend at least at the 95 percent confidence level of increasing weekly maximum air temperature for three out of the five meteorological stations studied in the decade of the 1970s, and also for the 40-year study period as a whole. MODIS-derived snow cover (percent of basin covered) measured on 30 April explains over 89 percent of the variance in discharge for maximum monthly streamflow in the decade of the 2000s using Spearman rank correlation analysis. Observed changes in streamflow may be related to increasing weekly maximum air temperature measured during the 40-year study period. The strong relationship between snow-cover extent and streamflow indicates that MODIS data are useful for predicting streamflow, leading to improved reservoir management.