From dry Wadi bed to flashflood: decoding climate-driven flood hazards in arid environments, Saudi Arabia
摘要
Flooding increasingly endangers the arid Wadi Ibrahim catchment that drains central Makkah. This study quantifies the evolving flood hazard under climate change by coupling CORDEX-downscaled rainfall (RCP 4.5 and RCP 8.5) with high-resolution two-dimensional HEC-RAS Rain-on-Grid modelling for 50-, 100- and 200-year return periods. Simulations adopt a dry-bed initial state and 48-h horizon to capture the ephemeral flash-flood cycle typical of the region. Results show a pronounced intensification of flood metrics. Present-day flood volumes rise from 18.9 × 106 m3 (50-year) to 24.8 × 106 m3 (200-year); these volumes almost double under RCP 4.5 and triple under RCP 8.5, reaching 44.5 × 106 m3 and 86.1 × 106 m3, respectively. Average inundation depth increases from 0.2 m today to 0.6 m (RCP 4.5) and 0.8 m (RCP 8.5). Spatially, high-hazard zones (> 2 m depth) expand from 7.2–9.8 km2 under current conditions to 5.3–12.0 km2 under RCP 4.5 and 9.5–16.6 km2 under RCP 8.5. Peak discharges for the 100- and 200-year events exceed the established Saudi Arabian envelope curve, evidencing non-stationary extremes. These findings highlight the need to update design standards and prioritize adaptive strategies, such as enlarged culverts, detention basins, and real-time early-warning systems; to safeguard lives, the Grand Mosque environs, and critical infrastructure against escalating flood hazards in a warming climate.