Assessment of climate-driven flood risks and damages in the Kashkan River floodplain

Flood losses in semi-arid Iran are expected to increase under climate change, yet quantitative projections remain limited for many interior basins. This study develops an integrated framework combining statistically downscaled CMIP6 projections, a hybrid HEC-HMS and LSTM rainfall-runoff model, non-stationary flood frequency analysis, one-dimensional HEC-RAS hydraulic modeling, and the DamageScanner module to appraise potential future fluvial flood economic damage and risk in the Kashkan River basin. Changes in flood frequency, intensity, inundation extent, and economic damages were assessed under SSP1-2.6 and SSP5-8.5 for near (2030-2060) and far future (2060-2090). The findings indicate increasing flood hazard under both scenarios, with stronger increases under SSP5-8.5, particularly after mid-century. Annual maximum cumulative precipitation is projected to increase by up to 46% by the late century. This hydro-climatic shift is associated with an increase in maximum river discharge of approximately 66% in the near future and 107% in the far future under SSP5-8.5 compared to the historical baseline. Consequently, the projected flood hazards are expected to cause substantial economic losses; Expected Annual Damage (EAD) is estimated to grow from a 2015 baseline of about US$1 million to US$7.5 million under SSP1-2.6 and US$18 million under SSP5-8.5 by 2090. Losses are heavily concentrated along the densely settled east bank of Pole-Dokhtar. These findings support the integration of flood hazard and damage maps into spatial planning and the prioritisation of riverside hotspots for adaptation investment.