Flood-prone area mapping using GIS-based analytical hierarchy frameworks for Ibadan city, Nigeria

Flood is one of the highly pronounced ruinous naturally occurring environmental hazards in which human lives and properties are gravely endangered. This study assessed areas prone to flood in Ibadan City, Nigeria. The study applied two multi-criteria analysis approach-Analytical Hierarchy Process (AHP) and the Fuzzy Analytical Hierarchy Process (FAHP) with the aid of GIS. Ten geomorphological physical characteristics agreed upon by experts as the major factors influencing the susceptibility of an area to floods formed the criteria maps used in this study. The natural breaks and geometrical interval clustering techniques were utilised to group the final flood-prone area maps into five categories-very low, low, moderate, high, and very high. The result indicated that over 50% of the study area either have low or moderate susceptibility to flooding. The clustering techniques showed some slight differences in the flood classifications where natural breaks consistently grouped more areas into the "very high" category and relatively fewer areas to "very low" category in comparison to the geometrical interval technique. Overall, at least 451 km(2) (about 15% of Ibadan) is highly or very highly prone to floods, and these areas are mainly concentrated in the urban and semi-urban regions of the study area. The findings and maps developed in this study would adequately serve as a planning guide for the policymakers on urban development and flood risk management to achieve sustainable development and management.