Flash flood and erosion hazards in Wadi Al-Sirhan catchment, northern Saudi Arabia

Abstract

Wadi Al-Sirhan, the largest catchment in Saudi Arabia, is a semi-arid basin that is highly susceptible to damaging flash floods and soil erosion because of its dry climate, strong convective storms, and limited vegetation. This study applies an integrated GIS-based morphometric and multi-criteria assessment to recognize and prioritize risk-prone areas within the proposed catchment. We conducted a thorough morphometric study of the entire basin and its 70 sub-catchments using a 30-m SRTM DEM, computing 24 parameters related to drainage, relief, and shape to assess hydrological behavior. For each sub-catchment, a Flash Flood Risk Index (FFRI) and a Compound Factor (CF) for soil erosion were then calculated using a rank-based multi-criteria approach to nine key morphometric characteristics affecting runoff and erosion. The Wadi Al-Sirhan catchment presents a low drainage density of 0.32 km/km ² , characteristic of arid regions, which provides rapid runoff generation and heightened flood and erosion susceptibility. Significant internal heterogeneity was discovered, nevertheless, with sub-catchments in the center and western regions (such as SC-32 and SC-33) showing extremely high sensitivity because of their Steep slope, high drainage density, and high stream frequency. According to prioritization, 52.0 % of the catchment area is highly vulnerable to soil erosion, and 88.6 % of the territory is at high to very high risk of flash floods. In 28 % of the land, there is a noticeable convergence of both hazards. The results support urgent conservation efforts in high-priority sub-catchments and provide a solid scientific basis for targeted risk mitigation, sustainable land management, and resilient infrastructure planning in northern Saudi Arabia.