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.
