Detection of earlier snowmelt in the Wind River Range, Wyoming, using Landsat imagery, 1972-2013

In the western United States snow has been melting earlier in recent decades due to warmer winter and spring weather. This is particularly noticeable in the Pacific Northwest and coastal areas, yet has been less obvious in locations farther inland. Using the historical Landsat image archive, snow cover was mapped in the Wind River Range (WRR) in northwestern Wyoming, from 1972-2013. The objective of this work was to estimate the temporal change in the rate of snowmelt in the Fremont Lake basin of the WRR for the 42-year study period. Much of the streamflow in Wyoming originates from melting snow in the WRR. Streamflow is a significant contributor to the water resources for the north-central part of the state and has tremendous societal and economic impacts especially during the prolonged drought that is affecting the western U.S. Consistent with the ongoing and severe drought, data from the Pine Creek Above Fremont Lake gauge show a striking reduction in cumulative stream discharge in the 2000s vs. the decades of the 1970s, 1980s and 1990s. Snow-cover depletion curves derived from snow maps created from Landsat imagery were generated for the period 1972-2013. MODerate-Resolution Imaging Spectroradiometer (MODIS)-derived standard snow-cover maps were also used to generate snow-cover depletion curves, from 2000-2013, to provide an accuracy assessment of the Landsat technique. Landsat-derived mean snow-cover depletion curves from 2000-2013 and from the three previous decades, show that snow cover in the Fremont lake basin is melting 16 +/- 10 days earlier, on average, in the 2000s compared to the period from 1972-1999. Increasing spring and summer nighttime air temperature is the likely driver of the earlier snowmelt documented in the Landsat record. (C) 2015 Published by Elsevier Inc.