Spatial assessment of groundwater variability and drought impacts on ATES system suitability in Spain

Study region This study is conducted across groundwater bodies within mainland Spain, as defined under the European Water Framework Directive. Study focus We conduct a preliminary, national-scale assessment of groundwater-body suitability for Aquifer Thermal Energy Storage (ATES) in Spain from a water-energy nexus perspective. The methodology is based on two complementary indicators derived from long-term piezometric records: (i) a Drought Stress Response Index (DSRI), reflecting aquifer reliability, resilience, and vulnerability over decadal time scales, and (ii) groundwater-level variability and long-term trends as proxies for hydraulic stability. Together, these indicators support a first-order screening of groundwater bodies from less suitable to more suitable conditions for ATES operation. New hydrological insight of the region The analysis of drought-response indicators reveals clear spatial patterns in aquifer vulnerability, resilience, and reliability across Spain, with only weak correlations with mean groundwater levels. Groundwater-level amplitude and trend analyses indicate that unstable conditions are concentrated in southern and eastern Spain, whereas northern regions generally exhibit more stable regimes. Building on these indicators, the results reveal pronounced spatial contrasts in ATES suitability, with generally more favorable conditions in northern regions and lower suitability in large parts of southeastern Spain, while extensive areas with intermediate suitability are also identified. Based on this national-scale screening, the study provides a preliminary assessment of ATES suitability for the main Spanish urban areas, offering an initial indication of where groundwater conditions are more or less favorable for ATES deployment.