Spatial Multi-Criteria Evaluation of Proportional Accountability of Flood Causal Factors and Vulnerable Areas in Makurdi, Benue State, Nigeria

Abstract

There have been considerable reports on flood frequency, vulnerability and risk especially on Makurdi. However, not much has been known about the proportional contribution of the causal factors and distribution among vulnerable areas. This aspect remains fundamental in flood disaster and risk management decisions and actions. It is on this premise that this study applied the spatial multi-criteria evaluation technique (SMCE). The four (4) broad categories of flood causative factors: Climatic (rainfall) , soil (textural distribution of clay and sand content), morphometric (slope, linear and areal) and Land Use / Land Cover (built-up land, bare land, farm land, vegetated land, wetland and water bodies/broad river) were used for the analytic hierarchy process and weighted sum overlay technique. The analysis revealed percentage contributions of the most effective flood causing factors as follows: Rainfall (44.89%), morphometry (34.02%), Landuse / Landcover (12.8%) and soil (6.28%). The weighted sum overlay result shows that low flood vulnerability areas occupy 43.11% (460.782 km 2 ), moderate flood vulnerability areas 31.13% (332.717 km 2 ) and high flood vulnerability 25.75% (275.238 km 2 ). Since this study identified rainfall as the major determinant of flooding it recommends that annual and seasonal rainfall predictions should be enhanced in Makurdi. Also, the area with high flood vulnerability which coincides with built-up area should drive the promotion of flood resilience city structures and enforced by relevant public institutions such as Federal Ministry of Environment, Urban Planning Departments, Works and Housing. Therefore, remediation actions can be applied for the high vulnerability areas while mitigation actions can be focused more on the moderate flood vulnerability areas.