The Mediterranean region is highly vulnerable to climate variability, with profound implications for water security. This study assesses the impact of four decades (1983-2023) of climatic fluctuations on land use and groundwater resources in the Wadi Fekan sub-watershed, northwest Algeria. Using standardized indices (SPI, CMI) and break detection tests on data from 11 rainfall stations, we identified a pivotal climatic shift between 1999 and 2006. This break initiated a wetter regime, leading to a 31.7% increase in rainfall. The resulting increase in runoff led to a measurable expansion of the main riverbed (+0.045% in land-use class). Concurrently, the alluvial aquifer experienced substantial recharge, with volumes rising from 17.997 km3 (2003-2013) to 25.615 km3 (2013-2023). However, spatial analysis revealed a paradox: despite overall wetter conditions, aridity intensified in the basin's center due to a Foehn effect, and the aquifer's net water balance remained negative over the study period. This indicates that groundwater overexploitation during prior droughts created a hydrologic deficit that recent rainfall has not fully offset. These findings demonstrate the persistent vulnerability of semi-arid aquifers to climatic stress and anthropogenic pressure, underscoring the critical need for sustainable management strategies that address both climate variability and historical overuse to mitigate future water crises.