Flood Risk Zone Identification Using Land Use/Land Cover Change Detection and AHP Analysis

Flooding is a prevalent disaster in both developed and developing nations, exerting a lasting influence on several regions in Lagos State. In this study, the geographical information system (GIS) technique and the analytical hierarchy process (AHP) of the multi-criteria evaluation (MCE) technique were used to create a floodplain map of Lagos State. Rainfall, land use land cover (LULC), slope, digital elevation model, flow direction, drainage density, normalized difference water index (Ndwi), and soil texture map were the eight parameters identified. The data about the factors were obtained from an online source and processed using the spatial analytic tools in ArcGIS 10.6.1. To calculate the relevant ranking weight, the elements were compared pairwise. The output consistency ratio (CR) was 2.7%, which is below the permitted limit of 10%. The weight percentage obtained was then utilized in the weighted overlay operation to identify the flood risk zone. Based on an analysis of the produced land use and land cover in 2020, 2022, and 2024, changes in water bodies were found to be proportional to changes in built-up areas, with a kappa coefficient of the dataset being 82.8%. From the results, up to 25% of Lagos State is covered by water bodies, 58% of the state's total land is in the high flood zone, and less than 1% is in the very high and low flood areas. Overlaying locations subsequently validated the result declared flood-threatened by the National Emergency Management Agency (NEMA), giving an agreement ratio of approximately 85% and found to fall within the high flood zones.