Managed aquifer recharge in confined multi-layer aquifers: a scalable framework for drought resilience in central Europe

Managed Aquifer Recharge (MAR), particularly Aquifer Storage, Transfer and Recovery (ASTR), can enhance groundwater resilience in confined multi-layer aquifers under drought stress. We develop an integrated and scalable framework to assess ASTR feasibility by combining (i) meteorological and groundwater drought analysis using the Standardized Precipitation Evapotranspiration Index (SPEI) and Standardized Groundwater Index (SGI), (ii) GIS-based multi-criteria decision analysis (MCDA) for recharge site suitability, and (iii) dynamic assessment of surface-water availability using ecological flow thresholds. Applied to the water-stressed Berlin-Brandenburg region, one of Germany's driest areas, where water supply relies heavily on induced bank filtration and faces emerging deficits. Results show that groundwater levels respond to climatic variability, supporting climate- informed ASTR planning. The MCDA identified 62.8 % of the area (2154 km 2 ) as viable for ASTR. Flow-threshold analysis at 27 gauges showed that specific high-potential downstream sites could provide mean annual recharge volumes of 1.6–4.3 Mm 3 , offsetting 6 %–79 % of local extractions at those locations, although these volumes decreased substantially (40 %–100 %) during severe drought years (e.g., 2018), highlighting the importance of capturing wet-period surpluses for reliable ASTR operation. At the catchment scale, total mean annual available recharge is 18.2–23.0 Mm 3 . Literature-based cost estimates (EUR 0.30–0.60 m −3 ) are substantially lower than regional drinking-water production costs (EUR 1.80 m −3 ), suggesting potential for substantial cost savings relative to conventional water supply, though precise economic benefits require site-specific validation.