Flash floods are a significant risk in arid regions, especially in the Mekerra Basin of Northwestern Algeria, where rapid urbanization and climatic variability contribute to increasing flood vulnerability. This study integrates the Analytic Hierarchy Process (AHP) with Geographic Information Systems (GIS) to assess flood risk susceptibility in the basin. Eight key factors including, elevation, slope, drainage density, distance from rivers, flow accumulation, land use, topographic wetness index (TWI), and maximum daily rainfall were evaluated to calculate a Flood Susceptibility Index (FSI), categorizing the basin into flood risk levels. The findings show that 52.30 % of the basin is at moderate risk, while 42.37 % is at low risk. High-risk zones, representing 4.72 % of the area, are mainly located near the main wadi, where low-lying terrain, dense drainage networks, and urbanization contribute to increased flood vulnerability. The model achieved an 81 % accuracy when validated against historical flood data from 1986 to 2007, using a comparison of predicted flood-prone areas with observed flood occurrences. High-risk zones near the main wadi require immediate mitigation, such as reinforced infrastructure, while moderate-risk areas need targeted flood measures like improved drainage systems. Low-risk areas should focus on long-term strategies, including land-use planning and maintaining green spaces. The results highlight the combined impact of human activities and natural factors on flood risk, underscoring the importance of improving infrastructure and land-use planning, particularly in urban areas like Sidi Bel Abbes a major city in the basin. These findings underscore the need for targeted flood mitigation in urban areas and offer guidance for policymakers in improving infrastructure, land-use planning, and resilience against floods in the Mekerra Basin and similar regions.