Exploring Geographical Information Systems (GIS) and Analytical Hierarchy Process (AHP) for the Mapping of Flood Prone Areas in Ikpoba-Okha Local Government Area, Edo State, Nigeria

Abstract

Flood susceptibility mapping is an important element of flood mitigation and prevention since it aids in the identification of the most vulnerable areas. The target is to develop a flood susceptibility/inundation map for the identification of flood risk zones in Ikpoba-Okha LGA, Edo State, Nigeria. Ten (10) thematic maps namely; Topographic wetness index (TWI), Elevation, Slope, Precipitation, Land use land cover (LULC), Normalized difference vegetation index (NDVI), Distance from river, Distance from road, Drainage density, and soil were employed for the study. The thematic maps were reclassified in order to obtain a uniform scale using the reclassification tool in Arcmap. To obtain the percentage weight of influence for each of the data, analytical hierarchy process (AHP) was employed to generate a pairwise comparison matrix which was validated using the index of consistency (IC). Thereafter weighted overlay method was employed to stack the reclassify maps in order to generate the final flood susceptibility map for the study area. The outcome of the study was the delineation of the study area through the generation of a flood prone map that helped to identify the specific areas that are prone to flooding. Overall, areas within the red spot are very highly susceptible to flooding while the green and yellow spot signifies areas with low and high susceptibility to flooding

Introduction

The Nigerian Meteorological Agency (NiMet) has warned of increased flooding in Nigeria, based on data from the Nigeria Hydrological Services Agency (NIHSA). Globally, flood frequency and severity have been rising due to climate change, greenhouse gas emissions, and human-driven land use changes. Floods are natural events that cannot be fully prevented but can be mitigated with proper planning and protection. Floods cause significant fatalities and long-term impacts like disease, starvation, and economic losses.

Early warning systems and flood susceptibility mapping are crucial for flood preparedness and mitigation. Flood susceptibility maps identify vulnerable areas using factors such as elevation, slope, land use, soil type, precipitation, and river proximity. The spatial scale of the study influences the selection of these factors.

The study focuses on Ikpoba-Okha Local Government Area (LGA) in Edo State, Nigeria, which has a tropical climate with distinct wet and dry seasons. Using Geographic Information Systems (GIS) and Analytical Hierarchy Process (AHP), ten key factors were analyzed and weighted to generate a flood susceptibility map.

Results showed the study area has a high runoff curve number (average 83), typical of urban areas with impervious surfaces, increasing flood risk. Digital Elevation Models (DEMs), slope, elevation, and topographic wetness index (TWI) maps were generated to understand terrain influence on flooding. Steeper slopes lead to rapid runoff and higher flood risk, while flatter areas allow better infiltration.

The study highlights the importance of integrating multiple environmental factors to accurately assess flood risk, inform public awareness, and guide mitigation strategies.

Conclusion

The findings of this study underscore the intricate interplay between environmental factors and flooding dynamics. Precipitation emerges as the primary driver of flooding, with its intensity, duration, and spatial distribution significantly impacting the likelihood and severity of inundation events. Soil characteristics, particularly infiltration capacity and moisture content, exert considerable influence on flood susceptibility by modulating surface runoff and groundwater recharge. Additionally, topographical features such as elevation and slope play crucial roles in determining flood risk, with low-lying areas and steep slopes often exhibiting heightened vulnerability to inundation. Land use and land cover patterns further shape flood dynamics, with urbanization and deforestation exacerbating runoff and reducing natural floodplain storage capacity. These findings underscore the complexity of flooding processes and emphasize the importance of adopting holistic, multi-disciplinary approaches to flood risk management that integrate knowledge from hydrology, climatology, soil science, and land use planning.

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Copyright

Copyright © 2025 Omosefe, E. B , Ilaboya, I. R . This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.