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Barnhart, Theodore B ¹ ; Livneh, Ben ² ; Gochis, David J ³ ; Molotch, Noah P ⁴

¹ University of Colorado, Boulder
² University of Colorado, Boulder
³ National Center for Atmospheric Research
⁴ University of Colorado, Boulder

Snowmelt is the primary source of surface water in the western United States and for approximately one sixth of the global population. Climate change is altering the magnitude of the mountain snowpack and the timing and rate of snowmelt. The Colorado Front Range imports water from the western slope of the Southern Rocky Mountains using twelve basin pairs on either side of diversions, which supply 23 trans-basin diversions in total. We ask if the basins contributing water to and receiving water from trans-basin diversions have different streamflow sensitivities to changes in snowmelt. We use the Variable Infiltration Capacity (VIC) model run at 1/16 of a degree from 1950-2013 using a gridded meteorological data set to simulate snow water equivalent and discharge for the pixels within these twelve basins. Interannual variability in these data sets are used to compute the sensitivity of discharge to changes in snowmelt dominated water flux, snowmelt rate and rainfall rate, to the soil for each grid cell in the domain. High-elevation grid cells show the greatest runoff ratio sensitivity to changes in snowmelt rate while low-elevation grid cells show the least sensitivity. High-elevation grid cells also have the strongest and most significant relationships. When the grid cell relationships are aggregated to the watershed level five of twelve catchment pairs have greater sensitivity on the contributing side while the remaining seven catchments do not show significant differences in sensitivity. Snowmelt dominated water flux is expected to decline with climate change, which will likely decrease proportional runoff more drastically in basins contributing to trans-basin diversions, which could strain trans-basin water transfer agreements.