Effect of Land Use on Wetland Degradation and Flood Occurrence in Makurdi Metropolis, Central Nigeria

Abstract

Globally, wetlands play a critical role in mitigating floods by absorbing and storing excess water, thus reducing flood peaks and preventing damage to surrounding areas. They also contribute to water purification by filtering pollutants, supporting biodiversity, and replenishing groundwater reserves. This study evaluates the impact of urbanisation on wetland degradation and flood vulnerability in Makurdi metropolis, Benue State, Nigeria, using Geographic Information System (GIS) and remote sensing from 1986 to 2023. Landsat 5 TM and Landsat 8 OLI images were classified using maximum likelihood. Wetlands were visually delineated for 1986 and 2023 using historical imagery in Google Earth Pro. Streamed networks, digitised from Google Earth Pro, were used to evaluate proximity to flood-prone areas. All datasets were re-projected using the Minna/UTM Zone 32N coordinate system to ensure spatial alignment and accuracy across the study area. All attribute data were exported to Microsoft Excel, where summary statistics were computed. Over this 37-year period, the wetland area reduced by 96.08%, from 40.10 km² in 1986 to 1.57 km² in 2023. Land cover analysis within the wetland areas shows a significant increase in built-up areas from 0.79 km² (1.9%) to 24.43 km² (58.4%), while vegetation cover decreased from 31.45 km² (75.1%) to 16.75 km² (40.0%). An overall accuracy assessment yielded 95.81% accuracy for 1986 and 90.14% for 2023, validating the classification results. Similarly, a strong spatial correlation between wetland loss and increased flood occurrences was identified in the south bank regions. Flood risk analysis revealed that 31.78% of buildings (62,694 buildings) are located within wetland areas, exacerbating flood risk in regions such as Nyiman and Achusa. These findings emphasise the importance of sustainable urban planning and wetland conservation to mitigate flood risks and environmental degradation in Makurdi metropolis. More importantly, integrating green infrastructure and promoting community awareness of the ecological and socio-economic importance of wetlands can help ensure a balanced approach to urban development and environmental sustainability.