Screening the Future Security of Groundwater-based Water Supply on the Scale of a Regional Water Supplier

Abstract Climate change alters the hydrological cycle, which may impair the replenishment of aquifers. Water suppliers need tools to examine whether available regional groundwater resources will sustainably meet the demands under future conditions. We present a screening framework that can be easily and quickly implemented - thanks to low model and data requirements. It uses a new indicator, the groundwater use index ( $$GWUI_N$$ ), relating the water demand of a month to the groundwater recharge in the catchment averaged over N preceding months. The framework was applied to a region in southwest Germany to assess possible changes of regional water resources by 2070 for a diversity of climate projections. We identified the main drivers of water demand and projected possible future development paths. Future groundwater recharge was estimated by means of a distributed soil-water-budget model informed by climate data of respective projections. Historical data were analyzed to determine appropriate averaging periods N for evaluating the $$GWUI_N$$ . Our assessment reveals that water supply is not secure. Despite the rather humid climate in the region, the absence of any irrigation agriculture, and a substantial share of water demand being covered by a long-distance water supplier, results for climate projections that agree with observed historical precipitation of the past 25 years indicate future demand-to-availability ratios that signal water stress for the supplier.