A Geospatial Analysis of Flood Risks and Vulnerability in Ogun-Osun River Basin, Nigeria

Abstract

The frequency and intensity of flood disasters have become serious issues in the development process as flood disasters have caused serious environmental damage, loss of human lives and wanton destruction of economic assets globally. Loss of human lives and development assets, rising costs of reconstruction efforts and associated hardship are putting the issue of disaster reduction and risk management higher on the policy agenda of affected governments, multilateral agencies and NGOs. The starting point of concrete flood disaster mitigation efforts is to identify the areas with higher risk levels and fashion out appropriate preventive and response mechanisms.

This paper proposes a GIS-based model for identifying flood-prone areas for the purpose of planning for disaster mitigation and preparedness, using a river basin as a unit of analysis. This model uses a number of physical, demographic and landuse data to identify areas and settlements that are vulnerable to flooding. Based on this multi-criteria model, areas, settlements and populations with varying degrees of vulnerability to flooding were identified and mapped. The model results showed that over 1,200 settlements harbouring over 13 million people are at grave risk of flooding. These vulnerable settlements and populations are mostly located within the coastal stretch, river valleys and urbanized parts of the study area. While the model proves to be usable for planning purposes, inclusion of population data at a finer level (Enumeration Areas) would improve the performance of this model by providing a near accurate estimation of population at risk as well as their spatial spread.