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GSFLOW and MODSIM-GSFLOW model used to evaluate the potential effects of increased temperature on the Carson Valley watershed and agricultural system in eastern California and western Nevada

June 18, 2021

The USGS developed an integrated river operations-groundwater model using GSFLOW and MODSIM GSFLOW to simulate streamflow derived from snowmelt, the distribution of surface water based on the existing prior appropriations water doctrine, supplemental pumping in response to surface water shortfalls, and the resulting surface water-groundwater interactions in the Carson Valley in California and Nevada. The model was used to evaluate the effects of increases in atmospheric temperature on snowmelt, streamflow timing, water availability, surface water and groundwater use, and agricultural evapotranspiration. The upper watersheds of the East Fork and West Fork of the Carson River were simulated using GSFLOW. The Carson Valley agricultural system was simulated using GSFLOW-MODSIM. The iterative ensemble smoother approach in PEST++ was used to adjust parameters, including irrigation rates and efficiencies, until an adequate match was obtained between simulated values and historical observations of streamflow, agricultural evapotranspiration, and groundwater head from 2000 to 2005. Earlier snowmelt and streamflow results in more water passing through the agricultural valley before the start of the irrigation season. Resulting surface water irrigation shortfalls, water distribution based on prior appropriations, return flows, and supplemental pumping results in a complex pattern of water deliveries and crop consumption. This USGS
data release contains all of the input and output files for the simulations described in the associated journal article. (https://doi.org/10.1029/2020WR027924).