Flood Hazard Vulnerability And Risk Assessment Using Multi Crite Ria Decision Analysis And Gis. A Case Of Shabelle River Basin South Ern Somalia.

Abstract

River floods are the most common and costly natural disaster, affecting nearly every country on the planet. Flooding along the Shebelle River in Southern Somalia has been a major challenge for community development organizations in the region. Such study will contribute decision making and prevention of flood hazards in the areas susceptible to it and improvement of the living environment of Shebelle river basin. The general objective of this study was to assess flood hazard vulnerability and risk using GIS-based Multi-Criteria Decision Analysis in Shebelle river basin. The seven different map layers was used to create flood hazard map(elevation map, slope map, drainage map, distance to river, rainfall map, soil map and geology map) was created, then raster layers, reclassifying raster layers, weighted sum and finally flood hazard map. The results obtained shows that 10.92%, 24.97%, 29.13%, 21.93% and 13.04% corresponds with very low, low, moderate, high and very high flood hazard areas. For flood vulnerability five different map layers was used (Land use/land cover, population density, distance to road, Global Man-Made Impervious Surfaces and Human Built-up Area Settlement Extent) to create flood vulnerability map. The results obtained shows that 45.98%, 29.28%, 12.67%, 11.42% and 0.65% corresponds with very low, low, moderate, high and very high flood vulnerable areas. Furthermore flood risk map was developed using the results obtained from flood hazard and vulnerability map. Based on degree to flooding, the importance of selected parameters were ranked to five flood hazard and vulnerability category, namely very low flooding, low flooding, moderate flooding, high flooding and very high flooding. The weight coefficients were determined for each parameter by Analytical Hierarch Process (AHP) and sum of ranked spatial information result the final flood hazard and vulnerability map of study area. The most important flood occurrence parameters are elevation (40.4%) and slope (22.6%). The results obtained shows that 27.6%, 30.9%, 23.6%, 12.1% and 5.7% correspond with very low, low, moderate, high and very high flood risk areas respectively for Shebelle river basin. Most of the basin are under very low, low and moderate flood risk, some small parts are under high and very high flood risk. Flood hazard, vulnerability and risk maps should be provided and distributed the authorities responsible for flood protection so that people are aware flood risk locations.