Groundwater depletion and saltwater intrusion under climate change

Coastal aquifers, such as the Grombalia aquifer in northeastern Tunisia, represent strategic freshwater resources that are increasingly stressed by intensive groundwater abstraction and climate change. These combined pressures exacerbate groundwater level decline and can accelerate saltwater intrusion, posing a serious threat to long-term sustainability of the aquifer. A comprehensive assessment of both piezometric evolution and salinity dynamics is therefore essential to support effective groundwater management. This study investigates the current state and future evolution of groundwater levels and salinity in the Grombalia coastal aquifer using a three-dimensional, variable-density numerical modeling framework. A SEAWAT model, coupling MODFLOW for groundwater flow with MT3DMS for solute transport, was developed to simulate freshwater–saltwater interactions. The model was calibrated against observed piezometric heads to ensure an accurate representation of groundwater flow dynamics, after which salinity distributions and freshwater–saltwater intrusion processes were analyzed. A 20-year transient simulation was first performed to reproduce historical groundwater level fluctuations and saltwater intrusion patterns, providing a robust baseline for future assessments. Then, scenario-based simulations extending to 2095 were carried out by forcing the groundwater model with climate change–driven recharge projections obtained from an ensemble of regional climate models (RCMs). Prior to their use, these projections were bias-corrected using local observational data to enhance their reliability at the aquifer scale. The simulation results reveal that climate change exerts a stronger influence on groundwater level decline than on the direct advancement of saltwater intrusion. Projected reductions in recharge under future climate scenarios lead to a substantial lowering of piezometric heads, which in turn indirectly promotes the inland migration of the saltwater wedge and increases chloride concentrations in key pumping wells. These findings highlight the critical role of recharge variability in controlling both groundwater availability and salinization processes in coastal aquifers. 

This work was supported by the PRIMA programme under grant agreement No. 1923, project Innovative and Sustainable Groundwater Management in the Mediterranean (InTheMED). The PRIMA programme is supported by the European Union.