Implications of observed changes in high mountain snow water storage, snowmelt timing and melt window

Study Region: Upper Rio Grande Basin, United States. Study Focus: Both measured and modeled hydrologic studies report warming-related changes in the hydrologic cycle. However, studies using measured data often rely on April 1 snow water equivalent (SWE) instead of peak SWE. To understand climate-related hydrograph shifts we investigate trends in maximum SWE, timing of maximum SWE and snow depletion and length of the snowmelt window using measured data with both linear regression and Mann-Kendall methods to provide an integrated understanding of the trends. New Hydrological Insights for the Region: Of 16 locations with the longest data record (1980-2018) in the region, more than half had significant declines in maximum SWE. Regional trends using all sites collectively showed a decline in maximum SWE of -0.4 cm/year. Maximum SWE was earlier at 10-13 of 16 sites, depending upon method. Trends at individual locations show a wide range in maximum SWE advancement (18-48 days). Regional maximum SWE advanced three weeks. Snowpack depletion was similarly early at more than half the sites. Although snowmelt occurs earlier, there was no change in the snowmelt window (days between peak SWE and no snow). The reduced maximum SWE may relate to reduced snowfall, increased sublimation or lower albedo associated with dust. We describe the ecological and social impacts of these observed shifts in snow amount and runoff timing for headwaters communities, water compacts, mountain ecosystems, and riparian vegetation.