Regional-scale assessment of climate-driven hydrological balance changes and implications for coastal aquifer recharge in south-eastern Sicily

Climate change is progressively altering the hydrological regime of Mediterranean coastal regions, with direct implications for groundwater recharge and the vulnerability of coastal aquifers to saltwater intrusion. This study assesses changes in the hydrological balance of south-eastern Sicily, with a focus on the Ragusa province, adopting a regional-scale approach rather than a single-basin analysis.

Historical climate data and future projections of temperature and precipitation were analysed to estimate the spatial and temporal evolution of the main components of the hydrological balance. Results indicate a marked decrease in effective precipitation, together with increasing temperatures and evapotranspiration. Under the high-emission RCP8.5 climate scenario, regional-scale groundwater recharge is projected to decline by approximately 40–45% from 2071–2100 relative to 1971–2000, with substantial spatial variability.

The strongest reductions are observed in coastal and low-lying areas, where the diminished freshwater input may significantly affect aquifer equilibrium. Such a deterioration of the regional hydrological balance represents a critical predisposing factor for saltwater intrusion, particularly in areas already subjected to intense groundwater abstraction.

These findings highlight the relevance of regional-scale hydrological balance assessments for identifying areas of increased vulnerability and for supporting sustainable groundwater management strategies in Mediterranean coastal environments under changing climatic conditions.