Impact of Droughts on Water Supply in US Watersheds: The Role of Renewable Surface and Groundwater Resources

We use a simplified water supply system model based on the water availability assessment via the Variable Infiltration Capacity (VIC) hydrologic model to analyze water supply droughts (WSDs), which are periods with deficient water supply. The model is applied to 27 representative watersheds of the contiguous U.S. to explore how different management strategies can be more effective in mitigating WSDs in watersheds with different drought propagation mechanisms. We find that water supply deficits during droughts (WSDDs) are generally the highest in the Great Plains watersheds, followed by the western U.S. watersheds, and lowest in the eastern U.S. watersheds. We show that different measures can be adopted to mitigate WSDs in different regions. Specifically, in the western U.S. watersheds, the conjunctive use of surface and groundwater can reduce WSDD, that is, increasing surface water utilization and using groundwater recharged through winter precipitation to supplement surface water supply during droughts. In the Great Plains region, water demands need to be brought down to sustainable levels; meanwhile switching from groundwater to surface water supply can significantly reduce WSDD as the alluvial aquifers in this region provide a stable baseflow, which can act as a steady source of water supply during droughts. In the eastern U.S. watersheds, the depletion of limited storage capacity during droughts can lead to WSDD for short periods of time, which highlights the need for expansion of storage capacity in this region.