Groundwater depletion under climate and human pressures: MODFLOW modeling and prospective scenarios for central Tunisia

Groundwater resources in arid and semi-arid regions face mounting pressure from population growth and agricultural intensification. In central Tunisia, the Sidi Bouzid North (SBN) basin relies critically on its shallow aquifer system to meet water demands. This study develops a numerical groundwater flow model using MODFLOW, calibrated over a 29-year period (1990-2019), to assess the current state of the aquifer and simulate its future evolution. Steady-state and transient calibrations yielded correlation coefficients of 0.97 and 0.95, respectively, confirming the model's reliability. The 2019 water balance reveals a structural deficit of 17.24 Mm3/year, reflecting increasing overexploitation since 1990. Two prospective scenarios were developed for 2050: a climate scenario incorporating an 18% rainfall reduction based on national climate projections, and an anthropogenic scenario combining reduced recharge with a continuation of the current exploitation trend. The climate scenario produces a modest average piezometric decline of 0.3 m, whereas the anthropogenic scenario results in a far more severe drop of 1.8 m, six times greater, underscoring that human pressure is the dominant driver of aquifer degradation. Peripheral basin areas are identified as the most vulnerable to drying. These findings call for urgent action, including withdrawal reduction, artificial recharge, and enhanced piezometric monitoring, to ensure sustainable groundwater management in this water-stressed region.