Impacts of Groundwater Decline on Aquifer Thermal Energy Storage Suitability in Spain

Aquifer Thermal Energy Storage (ATES) systems are among the technologies needed to decarbonize the heating and cooling of buildings. This study assesses the suitability of ATES systems of Spanish aquifers that are prone to groundwater level decline. The focus of this study is on aquifers that are affected by recurrent droughts and where groundwater availability and stability are critical constraints. These aquifers are identified and selected for detailed analysis within the framework of this study.Aquifer suitability is evaluated using thermal recovery efficiency as the primary performance indicator for ATES feasibility. The assessment is conducted under both present and future energy demand and groundwater level scenarios, accounting for projected changes in groundwater (phreatic) levels and external temperature conditions associated with climate change. Subsurface conditions are first characterized, including aquifer and aquitard properties and the degree of aquifer saturation.Future groundwater level scenarios are estimated using an established conceptual relationship between reductions in aquifer recharge and corresponding declines in groundwater levels, applied here using aquifer recharge projections for 2050. In parallel, future thermal demand scenarios for 2050 are derived for residential and tertiary buildings based on projected scenarios with changes in external air temperatures. These projections result in spatially maps of groundwater level change and thermal demand, which are subsequently used as inputs for ATES performance simulations.Coupled groundwater flow and heat transport modeling is then applied to simulate current and future thermal recovery efficiencies, enabling a direct comparison of ATES performance under evolving hydro-climatic conditions. Preliminary results include national-scale prediction maps of groundwater level decline and future thermal demand, highlighting regions where ATES suitability may decrease or remain viable under future groundwater level decline conditions.This work represents an extended integrated assessment of ATES suitability in Spain, explicitly linking groundwater availability, climate-driven changes, and thermal recovery efficiency. The proposed framework is expected to provide a decision-support tool that reduces uncertainty, helping private stakeholders and decision-makers to better understand where ATES systems may remain viable or become constrained under declining groundwater level conditions, and why, thereby potentially strengthening confidence in the responsible deployment of ATES in water-stressed regions.