Panacea to the catastrophe through mapping in anticipation of mitigating the flood magnitude along Wabi Shebele River Basin of Somalia

Somalia had experienced extreme flash floods in the recent years across the arid regions causing tremendous loss in lives and properties. However, the flood magnitude, depth, and frequency of occurrence is not yet quantified due scarce datasets. In this study, integration of observed and Climate Hazards Infrared Precipitation (CHIRP) satellite rainfall products along with various remote sensing raster data were used to improve hydrological model simulation outputs. The Hydrologic Engineering Center namely HEC-HMS and HEC-RAS models were used to simulate the rainfall-runoff processes and flood inundation, respectively using land use, soil, slope and Digital Elevation map (DEM) datasets. The HEC-HMS model calibration and validation of simulated flows generated by the model predicted good agreement with the observed flow with values of 0.79, 0.74 and 0.78, 0.78 for NSE, RVE, R2, and PEPF, respectively. The HEC-RAS model result indicates that the maximum flood depth and velocity were obtained at the floodplain area. The peak flood at 50, 100, and 200-year return period using General Extreme Value (GEV) distribution best-fit revealed 384m3s-1, 409m3s-1, and 434m3s-1, respectively. The 100-years peak flood discharge in a specific part of the river revealed a flood depth of 7.53m. The provision of levee mitigation measures revealed reduction of the flood extent by 35% and suggested as possible flood protection measures for the study area.