Flood susceptibility mapping in a data-scarce arid catchment of Southwestern Saudi Arabia

Flood susceptibility assessment in data-scarce arid catchments is constrained by limited hydrological observations and incomplete historical flood inventories. This study developed a Geographic Information System (GIS)-based Fuzzy Analytic Hierarchy Process (FAHP) framework to map flood susceptibility across the Najran Basin, Saudi Arabia. Eight conditioning factors were integrated: elevation, slope, drainage density, rainfall, land use and land cover, soil type, the Normalised Difference Vegetation Index, and the Topographic Wetness Index. The pairwise-comparison structure was established through a synthesis of published AHP and FAHP studies and subsequently converted into triangular fuzzy judgements. Drainage density, slope, and elevation received the highest final weights and together accounted for approximately 69.6% of the total weighting. The continuous flood susceptibility index was classified into seven categories, with High and Very High susceptibility concentrated mainly along the Wadi Najran corridor and within the low-gradient urbanised areas of the central and eastern basin. Validation used 35 documented flood-prone locations compiled from municipal reports for 2010–2024. The Success Rate analysis produced an AUC of 0.883, indicating strong spatial agreement between the ranked susceptibility surface and the available flood-location inventory. The resulting map provides a basin-scale susceptibility baseline for spatial screening and the prioritisation of more detailed flood investigations in a data-scarce arid environment.