Flood Risk to Roads in Aden, Yemen: From Exposure to Expected Annual Damage

This study quantifies flood risk to the road network of Aden Governorate, Yemen, under present and future climates using the NISMOD workflow (snail toolkit) and open data, and identifies where adaptation investment pays. Of the 522.98 km mapped network, 139.04 km (26.59%) lies within the 100-year flood hazard area, concentrated on the N4 corridor and the coastal plain. Expected annual damage (EAD) under current climate is 1.96M USD/yr for coastal flooding (WRI Aqueduct), 0.9-1.1M USD/yr for wadi-flash flooding (JRC), while riverine flooding is zero across all three GCMs - confirming empirically that Aden has no big-river risk. Coastal EAD rises by 16% (2030, RCP4.5) to 69% (2080, RCP8.5), reaching 3.32M USD/yr; damage deeper than 2 m drives about 80% of losses and nearly doubles by 2080. Screening six adaptation options (Hickford et al. 2023) shows network-wide protection is uneconomic (BCR < 1), whereas targeting the top-20% EAD corridors - four segments carrying 97% of fluvial risk - flips the economics: swales (BCR 14.9, NPV +8.1M USD) and drainage rehabilitation (BCR 4.5, NPV +7.1M). The outputs recommend targeted investment (~7.8M USD, repaid in about seven years of avoided losses), phased corridor protection and early warning, and provide a reproducible open workflow transferable to other Yemeni cities and to teaching. This record contains the full report and the presentation.