Spatial Decoupling of Climatic Recharge Opportunity and Groundwater Response in an Alluvial Fan: Implications for Regional Managed Aquifer Recharge Screening

Groundwater recharge constrains sustainable aquifer use yet cannot be directly measured across entire basins. Recharge is often represented as a single recharge-potential surface, which can conflate favorable recharge conditions with the subsequent aquifer response. Here, we present a dual-indicator framework that explicitly separates climatic recharge opportunity from groundwater response. A climatic water-balance proxy (RWB) was used to represent recharge opportunity, whereas median annual groundwater-level fluctuation (MedAF) provided an independent observation-based indicator of regional aquifer response. Machine-learning models were used to emulate the spatial organization of RWB and to classify MedAF using climatic, soil-hydraulic, terrain, hydrogeomorphic, and land-cover predictors, with rigorous spatial validation. Applied to the Dél-Békés sector of the Maros alluvial fan (Hungary), both models achieved areas of applicability exceeding 95% of the basin, although observational support for MedAF varied with proximity to the 57 monitoring wells. Despite their physical connection, the two indicators showed limited spatial correspondence, agreeing across only 35.7% of the area. SHAP attribution for the RWB emulator emphasized soil-hydraulic, hydrogeomorphic, and land-cover predictors, whereas the MedAF classifier was associated more strongly with climatic and topographic predictors. Applicability-constrained screening identified 100 candidate managed aquifer recharge (MAR) sites covering 18.03 km2. By separating recharge opportunity from groundwater response, the framework provides a potentially transferable strategy for regional groundwater assessment and first-stage MAR screening, helping prioritize areas for subsequent site-specific investigation in heterogeneous alluvial aquifers.