FLOOD HAZARD MAPPING UNDER CLIMATE CHANGE USING MIKE FLOOD: RIBB CATCHMENT, ETHIOPIA

Abstract

Climate change is expected to increase both the magnitude and frequency of extreme precipitation events, which may lead to more intense and frequent river flooding. This flooding may cause tremendous impact on life, property and historical sites. Therefore, this paper tries to show the extent of flood hazard on Fogera floodplain. A coupled 1D-2D hydrodynamic model, MIKE FLOOD was used to simulate the flood inundation extent and flooding depth in Ribb catchment, Ethiopia. This study was conducted to investigate the flood extent and depth in the area for different flow conditions derived from the historical flow data of the Ribb River in Fogera floodplain. MIKE FLOOD hydrodynamic modelling coupled with a hydrological model, SWAT was used to simulate the floods hazard maps under near-term and mid-term future climate scenarios. Near-term and mid-term future climate scenarios constructed from the bias corrected outputs of GCMs for 2030’s and 2060’s. The output from this research shows that catchment will get warmer and wetter in future. Both the minimum and maximum temperature of the catchment projected to increase in future. Similarly, average annual rainfall is also projected to increase in future is insignificant, higher in near-term and lower in mid-term in the future. The dimensionless inflow hydrographs for 100 years return flood were derived from an output of SWAT that were then fed into MIKE FLOOD model to generate the flood hazard maps in the catchment. The intensity of annual floods has shown an increasing trend for RCP 4.5 scenarios compared to the baseline period. The model was set up and calibrated from historical hydrometeorological data as well as measured river cross section data and Lake Tana water level. The result of Flood frequency analysis showed that a flow value of 290 m 3 /s for historical, 346 m 3 /s for near-term and 367 m 3 /s for mid-term for return periods of 100 years. According to the food map, the flooded area are 57.72 km 2 for base period, 59.3 km 2 for 2030’s and 61.01 Km 2 for 2060’s and a depth of 4.23m for base period, 4.68m for 2030’s and 4.96m for 2060’s inundated by the flood