San Joaquin Valley Irrigation District Vulnerability to Groundwater Overdraft Based on Surface Water Allocation and Consumptive Water Use

California's San Joaquin Valley is a global leader in food production, but is highly vulnerable to hydroclimatic variability and water scarcity. Historically, local irrigation districts have relied on groundwater to augment surface water supply, but overdraft and degradation have resulted in new regulatory limits on groundwater use through the Sustainable Groundwater Management Act (SGMA). Each irrigation district (ID) is unique, with a complex combination of history, customer base, surface water portfolio, size, location, political capital, and socioeconomic status. As such, each ID is uniquely vulnerable to imposed groundwater scarcity and hydroclimatic shocks. The objective of this study is to spatially resolve how ID surface water allocations and consumptive water use contribute to groundwater overdraft vulnerability and its implication for sustaining agricultural production and local communities in an uncertain future. It also quantifies total applied water (TAW), consumptive water use (CWU) and groundwater overdraft per ID for the 2014 drought year by using crop classification data and a water footprint model to calculate CWU within ID boundaries and assumes that California appropriative water right's allocation data are representative of TAW for each irrigation district to deduce groundwater reliance. If TAW amounts are insufficient to meet CWU demands, then IDs are groundwater reliant and potentially vulnerable to system shocks. Increased deficit is inversely proportional to vulnerability and, when coupled with socioeconomic status, is indicative of area requiring additional support via SGMA provisions. This study can assist policy decision-makers and stakeholders of IDs that are prone to not meeting SGMA targets by 2040 and to identify components of the food-water system capable of reducing overall vulnerability.