Climate change is a growing concern for water resource management. Among water bodies that could be most affected by changes in future climate, great attention must be paid to the aquifers, which many cities and agricultural activities rely on for the necessary freshwater. This work aims to evaluate the impact of climate change on a Tunisian aquifer, one of the pilot sites investigated in the InTheMED project, part of the PRIMA program of the European Union. First, historical temperature and precipitation data at daily scale and groundwater levels at monthly scale recorded in the period 1976-2020 were collected. Then, a two-dimensional finite-difference numerical model of the aquifer was developed and calibrated using MODFLOW. The groundwater numerical model reproduces the whole basin, from the recharge area to the outlet in the Mediterranean Sea. The area is agricultural intensive with a high demand for water. For this reason, the model required a calibration of hydraulic conductivity, recharge and pumping rate. After the calibration, the numerical model was able to estimate the groundwater flow and groundwater levels across the entire basin. To estimate the future climate, different combination of General Climate Models (GCMs) and Regional Climate Models (RCMs) were analyzed. In particular, 17 GCM-RCM combinations of the EURO-CORDEX initiative and according to two Representative Concentration Pathways, the RCP4.5 and RCP8.5 scenarios, were used. Daily mean temperature and precipitation projections, for the period 2006- 2100, were downscaled and bias corrected with reference to the meteorological historical data. These data were then used as input for the calibrated groundwater flow model, keeping water withdrawals from existing wells at 2020 values. The results are presented with reference to the local variations of the water table between the historical and future periods and to their uncertainty due to the variability of the projections of the 17 GCM-RCM combinations. This work was developed under the scope of the InTheMED project. InTheMED is part of the PRIMA programme supported by the European Union’s HORIZON 2020 research and innovation programme under grant agreement No 1923.

This work was developed under the scope of the InTheMED project. InTheMED is part of the PRIMA programme supported by the European Union's HORIZON 2020 research and innovation programme under grant agreement No 1923.