Purpose
The purpose of this paper is to prepare flood hazard map and show the extent of flood hazard under climate change scenarios in Woybo River catchment. The hydraulic model, Hydrologic Engineering Center - River Analysis System (HEC-RAS) was used to simulate the floods under future climate scenarios. The impact of climate changes on severity of flooding was evaluated for the mid-term (2041–2070) and long-term (2071–2100) with relative to a baseline period (1971–2000).
Design/methodology/approach
Future climate scenarios were constructed from the bias corrected outputs of five regional climate models and the inflow hydrographs for 10, 25, 50 and 100 years design floods were derived from the flow which generated from HEC-hydrological modeling system; that was an input for the HEC-RAS model to generate the flood hazard maps in the catchment.
Findings
The results of this research show that 25.68% of the study area can be classified as very high hazard class while 28.56% of the area is under high hazard. It was also found that 20.20% is under moderate hazard and about 25.56% is under low hazard class in future under high emission scenario. The projected area to be flooded in far future relative to the baseline period is 66.3 ha of land which accounts for 62.82% from the total area. This study suggested that agricultural/crop land located at the right side of the Woybo River near the flood plain would be affected more with the 25, 50 and 100 years design floods.
Originality/value
Multiple climate models were assessed properly and the ensemble mean was used to prepare flood hazard map using HEC-RAS modeling.
Flood susceptibility mapping plays a key role in planning flood mitigation. Floods may not be avoidable due to future climate changes. The Bilate catchment in Ethiopia is vulnerable to flood disasters and it is used as a case study in this project. The analytical hierarchy process (AHP) under multi-criteria decision analysis (MCDA) is used to develop the flood susceptibility map of the Bilate catchment. It was accordingly found that factors such as slope, rainfall, land use/land cover (LULC), elevation, topographic wetness index (TWI), soil type (ST), sediment transport index (STI), drainage density (DD), stream power index (SPI), and distance from the river (DR) have significant effects on the flood intensity in the Bilate catchment. The output maps were developed using ArcGIS. The prepared flood susceptibility map was classified into five classes such as very low, low, moderate, high, and very high covering 9.3, 32.6, 41.2, 10.8, and 6.1% of the area, respectively. The flood susceptibility map reported in this research is a great resource for relevant parties, including government and non-governmental organizations, to evaluate the impacts of flooding in the Bilate catchment and throughout the nation. The flood identified in this research may also be used as a reference to flood-related studies.
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