Satellite-Monitored Snow Cover in Western North America: A Comparison of Water Year 2015 to Median Conditions

Snow covered area (SCA) is readily monitored via satellites, and can illustrate complex spatial patterns of accumulation and melt that cannot be captured via point measurements.  Along with its important relationship to total water supply, snow also insulates surface soil horizons, provides protection for plant root systems during freezing events, and can delay the onset of soil drying and the fire season.  Traditional snow course and snow pillow measurements illustrated that the water year of 2015 saw snow levels that were substantially below normal in much of western North America.  However, the determination of a 'normal' SCA pattern (and the subsequent determination of what is abnormal) for a region requires the processing and analysis of vast amounts of spatial data, and is often not logistically feasible.  Using emerging technologies for processing massive spatio-temporal data, we calculated the near-term (2000-2015) normal monthly snow covered area at 500 m spatial resolution for more than 4.2 million km2 to illustrate how the water year of 2015 departed from typical conditions in the eight major hydrologic basins of western North America. Over the 96 months/basins available for analysis, 27 new monthly minimums for SCA were recorded in the water year of 2015. The most severe departures from the near-term normals were in the more coastal and southern basins. (KEYWORDS:  Remote sensing, snow covered area, climatology, snow drought)