Morphometric and Geospatial Analysis for Flash Flood Susceptibility Assessment in Wadi Al-Disha, Northern Saudi Arabia: Insights from a Dual Model

Abstract

Flash floods represent an extreme hydro-geomorphological hazard in the arid and semi-arid regions in northwestern Saudi Arabia, presenting major risks to significantly expanding urban regions, infrastructure, and sustainable development projects of Saudi Vision 2030. The present study assesses the flood susceptibility of the Wadi Al-Disha catchment (4212.81 km2) using a high-resolution 12.5 m spatial resolution ALOS-PALSAR digital elevation model (DEM). A dual-model approach, combining the scale-dependent Morphometric Ranking Method and the scale-independent El-Shamy approach, was applied over district 18 sub-catchments to investigate, analyze, and calculate 15 hydro-morphometric effective parameters. The Ranking Method model assigned sub-catchment SC-18 to the high-flood susceptibility zone, SC-4 as a low-flood susceptibility unit, and the rest of the 15 sub-catchments as moderate risk, with SC-9, the largest sub-catchment, scoring highest among the moderate rank, just below the high-susceptibility rank threshold. On the other hand, the El-Shamy Approach model defined SC-3 and SC-8 as high-flood susceptibility classes, while the remaining 16 sub-catchments reflect moderate-flood susceptibility classes. This proposed assessment is a physically-based susceptibility evaluation extracted from terrain morphometry; it does not consider socio-economic exposure or hydrological (rainfall–runoff) information, which we identify explicitly as scope boundaries below. Comparative validation with a regional study states that a bifurcation ratio indicates that tectonic rifting impacts bifurcation parameter values (Rb>4.0), forcing the El-Shamy Approach model to underestimate susceptibility in structurally complex, high-relief landscapes. To underestimate the impact of these flood susceptibilities and secure sustainable infrastructure in the very close Prince Mohammed bin Salman Royal Reserve, the study suggests designing targeted dams in rapid-velocity headwaters and creating an early warning system on the plateaus upstream.