Flood Susceptibility Mapping (Weighted Overlay Analysis)

Lagos, Nigeria is "blessed" to have very few environmental disasters, but flooding has proven to be the most destructive recurring disasters affecting the island state. The lack of adequate urban planning, and flood alert systems have led to recurring losses from established flood prone areas. Ikorodu is a local government area of Lagos, with its own fair share of chronic flooding incidents. in 2022 alone, an estimated 24,000 households were affected by floods.

One of the methods commonly used to analyse susceptibility, at data-poor regions (which do not support more sophisticated flood modelling techniques) is multi-parametric weighted overlay assessment. This considers the logical weighing of multiple flood-determining topological parameters to in a bid to assess susceptibility.

In this study, these methods are applied to derive a susceptibility map of Ikorodu LGA, Lagos. One of the most affected by floods in recent years.

Elevation, Slope, Land Cover, Rainfall, distance from small rivers and major water bodies are reclassed using the same classification schema, then weighted (assigning appropriate logical expert based weights), to derive the susceptibility map displayed in the web app below.

Below is a catalogue of the parameters used Elevation, Slope, Distance from major waterbody, Distance from minor waterbodies and Tributaries, Land Use Land Cover and Rainfall.

To arrive at a final susceptibility map, Weighted Overlay Tool in ArcGIS Desktop 10.7 was used, and weights were assigned based on a pairwise comparison Analytical Hierarchical Process

Further elaboration will be done in a soon to be released research article.