Spatial analysis of flood risk zones in Osun State, Nigeria

The study assessed the spatial analysis of flood risk zones in Osun State, Nigeria. The study made use of landuse/land cover data, elevation data, soil types and flood dates to compute the flood risk zones in Osun State, Nigeria. Descriptive statistics were applied for the study. Findings showed that in 2017, flood was detected in 16 LGAs of the state, comprising Iwo, Egbedore, Bolorunduro, Boripe, Ife North, Aiyedire, Ejigbo, Ila, Irepodun, Irewole, Isokan, Odo-Otin, Ola Oluwa, Osogbo LGAs which were 13 in number. These increased to 30 LGAs in 2023. Some towns identified included Esa Oke, Oranran, Bode Osi, Ode-Olowo, Ajebandele, Olode Ifon, Modogbon, Aketa and Ikoyi. Between 2017 and 2018, flood extent increased from 0.076 sq. km to 0.078 sq. km while in 2019, a marked increase of 0.293 sq. km was discovered and in 2023, it was 1.348 sq km. between 2017 and 2023, central and western LGAs such as Osogbo, Ede North, Ede South, Ife Central, Iwo, Isokan, and Aiyedire emerged as flood recurrent hotspots due to low-lying terrain, urbanization, and poor drainage. Eastern LGAs such as Oriade, and Obokun were less affected due to higher elevation and vegetation cover. Moreover, annual flood-impacted LGAs increased with increasing time. Similarly, the flooded area increased from 2017 to 2023, exposing the weakness of current structural measures under extreme rainfall. The study thus recommended that the government should enforce floodplain zoning that can restrict high-density settlements in very vulnerable zones; adopt nature-based solutions which can protect wetlands and expand urban green spaces for natural water retention; and control land use expansion to implement urban containment policies to limit impervious surface growth.