Water supply and demand balancing and forecasting in a semi-arid region of Algeria using the WEAP model: a case study of El Bayadh province

El Bayadh province, situated in southwestern Algeria, faces significant environmental challenges, including desertification, land degradation, and natural water scarcity, owing to its arid and semi-arid climate, which impedes the achievement of water-related Sustainable Development Goals. In such regions, decision-makers need methodologies that will allow them to develop a shared vision for the future of water resources, prepare for uncertainties, and adapt to ever-evolving challenges. This paper aims to assess water availability and demand under multiple scenarios that could plausibly unfold in the future, considering uncertain factors, such as climate change, policy options, technological development, and human behavior change, using the Water Evaluation and Planning System (WEAP) model. The study findings indicate a significant water supply–demand gap, resulting in substantial unmet water demand. Furthermore, the results demonstrate that water scarcity already impacts some agricultural areas. The results highlight the need to develop long-term strategies for the worst-case scenario and enhance preparedness for all response measures. Several adaptive solutions are proposed through this study, which can help water managers handle complex and interlinked water challenges.