In semiarid regions, population growth, urbanization, industrialization, agricultural expansion, and climate change exert increasing pressure on water resources. The Merguellil watershed in central Tunisia faces frequent droughts and extensive downstream agricultural activities, making sustainable water resource management critical. The watershed's water resources include the El Haouareb dam, which satisfies a small portion of public irrigation, and four aquifers (Kairouan, Bouhafna, Haffouz, and Ain_elBeidha), which supply the private irrigated area, drinking water, and transfers to coastal regions. To analyze the current and future (up to 2050) water balance, a Water Evaluation and Planning System (WEAP) model was developed, incorporating a constrained optimization algorithm to allocate water among competing demands in a basin. Agricultural water demand was estimated using MODIS satellite imagery to determine crop coefficient (Kc). The baseline scenario (2000-2020) revealed a gradual groundwater storage decline of 500 million m3 per year. Future scenarios included a climate change scenario (RCP4.5), two anthropogenic scenarios (2% annual increase in irrigated area and progressively decreasing water transfers to coastal regions), and management scenario (interconnection of the El Haouareb and Sidi Saad Dams). Results indicate that anthropogenic scenarios exacerbate groundwater depletion, reducing storage to 2 billion m3 by 2050, surpassing the impact of climate change. In contrast, the management scenario improved groundwater recharge and irrigation efficiency, highlighting the importance of integrated strategies. These findings emphasize the need for sustainable water management to mitigate water scarcity in the region.