Flood Hazard Mapping under SSP Emission Scenarios Integrating HEC-HMS and HEC-RAS Modeling in Afiya River Catchment, Southern Ethiopia

The occurrence, strength, and geographical spread of flooding events are greatly affected by climate change. Rising temperatures, changing precipitation patterns, and increased extreme weather events are likely to increase the severity and frequency of flood risk. The study is to assess flood risk mapping for the Afia River Basin using projected climate change scenarios SSP2–4.5 and SSP5–8.5 for the mid-2050s (2041–2070) and late 2080s (2071–2100). Using HEC-HMS and HEC-RAS, flood scenarios and mapped flooded areas for different return intervals (50 and 100 years), were modelled. The results show notable differences in flood risk levels between the scenarios. The total expected flooded area over the 50-year period in the 2050s is projected to be 117.92 ha in SSP2–4.5 and 129.13 ha in SSP5–8.5. The flooded area increases to 155.01 ha and 165.15 ha for the 100-year return period. By the 2080s, these areas further expand, with 50-year return periods showing inundation areas of 151.84 ha for SSP2–4.5 and 158.27 ha for SSP5–8.5, and 100-year return periods reaching 178.72 ha and 186.50 ha detailed assessment of flood depths reveals that in the 2050s, low hazard zones (D < 0.6 m) range from 86.35 to 96.60 ha, while very high hazard zones (D > 3.5 m) span from 4.95 to 4.98 ha. By 2080s, low-hazard areas increase to 114.42 and 119.98 ha, with very high-hazard areas extending from 6.10 to 6.39 ha. The combination of HEC-HMS and HEC-RAS modeling offers a strong platform for simulating and studying potential flood scenarios.