Modeling Climate and Anthropogenic Controls on Groundwater Recharge, Baseflow, and Spring Discharge in a mountainous volcanic Aquifer in the Mediterranean Area (Northern Etna, Italy)

Groundwater-fed river systems in mountainous regions are particularly vulnerable to the combined effects of climate variability and groundwater abstraction. Yet, quantitative assessments are often hindered by limited data availability, especially when the water table lies deep below the topographic surface. This study investigates groundwater–surface water interactions in the Northern Etna volcanic aquifer (Sicily, Italy), a UNESCO World Heritage Site that sustains the Alcantara River baseflow and supplies water for civil and agricultural uses.

A regional groundwater flow model was developed using MODFLOW 6, adopting an equivalent porous-medium representation of the fractured basalt aquifer under data-scarce conditions. The model was calibrated using PEST under steady-state conditions, using hydraulic head observations, and validated in transient mode against monthly discharge measurements from a major drainage gallery over the period 2009–2022. Scenario simulations were performed to quantify the effects of current groundwater abstractions and projected climate-driven recharge changes.

Model results show that current groundwater abstractions reduce spring discharge by approximately 23–37% (mean ≈30%). No significant long-term trend in baseflow is observed over the 2009–2022 period, suggesting that historical baseflow variability reflects the integrated aquifer response to recharge, storage and abstraction processes rather than a sustained climatic forcing.

Conversely, simulations driven by EURO-CORDEX climate projections reveal a substantial future decline in groundwater availability. Drainage gallery discharge is projected to decrease up to 23% in the near future (2021–2050) and up to 40% in the far future (2041–2070), depending on the emission scenario. These results highlight increasing stress on groundwater resources and reduced aquifer–river connectivity during prolonged droughts, with potentially severe impacts on groundwater-dependent ecosystems.

Despite inherent limitations related to data scarcity and necessary conceptual assumptions, this study demonstrates that regional numerical modeling can provide robust, management-relevant insights into mountainous aquifer systems. The proposed framework supports adaptive groundwater management strategies aimed at preserving river baseflow and ecosystem services under changing climatic conditions.