Flood susceptibility evaluation of arid coastal basins along the Northwest Coast of Egypt

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Abstract

Flash floods are among the most critical natural hazards in arid regions, where limited infiltration capacity and intense episodic rainfall generate rapid runoff and severe flooding. Egypt’s Northwest Coast, particularly the Sallum–Alexandria corridor, faces growing flood risks under changing climatic conditions, posing challenges to sustainable water and land management. In this study, we present an integrated assessment of flood hazard severity and geomorphological susceptibility across seven major arid coastal basins (>500 km²) using an integrated framework of Geographic Information Systems (GIS), remote sensing (RS), and hydrological and hydraulic modeling. Basin morphometry was derived from SRTM-based DEMs and analyzed through WMS 11.0 to extract 45 parameters describing geometry, drainage, relief, and texture. Rainfall trend analysis (1979–2020) demonstrated a significant increase in precipitation intensity over the last decade, with HYFRAN-PLUS employed to estimate 100-year return periods. Hydrological simulations revealed Basin 2 (Wadi El-Harika) produced the highest peak discharge (800 m³/s), while Basins 6 and 7 generated minimal runoffs. Conversely, hydraulic modeling indicated that Basins 5, 6, and 7 experienced the greatest inundation depths (up to 30 m), highlighting a disconnect between runoff volume and flood severity due to local topographic and drainage conditions. The results emphasized the need for basin-specific analysis and demonstrated that flood hazard severity could not be inferred from runoff magnitude alone. The proposed integrated framework provided a robust physical basis for flood hazard and geomorphological susceptibility assessment in arid coastal basins and offers a foundation for future flood risk or vulnerability analyses through the incorporation of exposure and adaptive capacity indicators.

Keywords

climate change / flash floods / hydrological and hydraulic modeling / flood hazard assessment / geomorphological susceptibility / arid and semi-arid basins / northwest coast of Egypt

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