Can reservoir and groundwater storage buffer the impacts of climate-induced declines in snowpack storage for agriculture and the environment? Insights from the Walker River Basin

Abstract

Climate-induced declines in snowpack storage have profound consequences for snowmelt-dependent river basins globally, including those in the western United States. These basins face the risk of economic losses in agriculture and environmental damage due to disrupted instream flows. To mitigate these potential losses, two strategies are commonly employed: enhancing built reservoir storage capacity and increasing groundwater use during the irrigation season. However, implementing these strategies carries the risk of exacerbating instream flow disruptions and compromising the sustainability of aquifers. This article develops a hydro-economic optimization model of Nevada's Walker River Basin (WRB) and uses it to examine the impact of storage capacity and groundwater management on mitigating economic losses in agriculture caused by altered snowmelt-driven inflows. The model accounts for environmental constraints on instream flows that limit water availability for agricultural use. Results show that the WRB is projected to experience a decline in irrigated farm acreage and agricultural output due to reduced snowpack storage. The findings also indicate diminishing returns on reservoir capacity investments, while highlighting the increased value of these investments when groundwater pumping is constrained due to aquifer sustainability concerns. Results show that upgrading existing reservoir capacity by not more than 1.5% in a free water leasing market could protect upwards of 94% and 83% of baseline agricultural income when the basin faces future climate-induced early season snowmelt-driven flow timing, and reduced streamflow, respectively, while managing the basin for hydrologic and environmental constraints.