Flood hazard mapping under a climate change scenario in a Ribb catchment of Blue Nile River basin, Ethiopia

Abstract

The present study was carried out to identify the extent of flood hazard on the Fogera floodplain in the Ribb catchment of the Blue Nile River basin in Ethiopia. A coupled 1 dimensional (D) and 2D hydrodynamic model (i.e., MIKE FLOOD) was used to simulate the flood inundation extent and flooding depth under climate change scenario in the study area. MIKE FLOOD coupled with a SWAT was used to simulate the floods hazard maps under short-term (2030s) and long-term (the 2060s) future climate projections for the RCP4.5 scenario. The results were revealed that the future minimum and maximum temperature can be increased to 1.99 °C and 2.65 °C, respectively. The average annual rainfall can be increased in the future. The dimensionless inflow hydrograph was best fitted with Gumbel distribution for the 100 years return period. This was derived from an output of the hydrological model and then fed into MIKE FLOOD to generate the flood hazard maps. The intensity of annual floods was indicated an increasing trend under the RCP4.5 scenario. The model was calibrated using the historical hydro-meteorological data, measured River cross-section data, and Lake Tana water level. The result of flood frequency analysis showed that a flow value of 100 year return period can be expected to 290 m3/s, 346 m3/s, and 367 m3/s for historical, short-term, and long-term time periods, respectively. The prepared flood hazard map indicated that the flooded area can be expected to 57.72 km2, 59.3 km2, and 61.01 km2 for the base period, 2030s, and 2060s, respectively, while the depth of inundated flood flow in the study area may be anticipated to a depth of 4.23 m, 4.68 m, and 4.96mfor similar time periods, respectively. Therefore, this study will be helpful for the decision makers to take the decision about the planning for the flood mitigation measures in the study region.