Lokoja, the capital of Kogi State, Nigeria, situated at the confluence of the Niger and Benue Rivers, has experienced rapid urban expansion alongside heightened environmental risks, including flooding and ecosystem degradation. Using multi-temporal Landsat imagery (2000, 2010, 2020, 2024), Random Forest classification, and landscape metrics, this study analyses spatio-temporal patterns of urban growth and fragmentation in this underrepresented mid-sized African city. Urban land cover expanded from 6668 ha in 2000 to 15,985 ha in 2024 (net ~140% growth), following a non-linear trajectory of rapid expansion (2000–2010), partial consolidation (2010–2020), and renewed growth with intensified fragmentation (2020–2024). This growth caused severe ecological impacts: dense forest declined by 99.7% (from 373 ha to 1 ha), woodland by 73.9%, and core natural land cover by 23% to 13.8% of the landscape, below critical ecological thresholds. Edge density rose by 121%, exacerbating urban heat, runoff, and biodiversity loss, while apparent gains in grassland largely reflect secondary succession rather than recovery. This study recommends enforcing development restrictions below 10 m in elevation, with 100 m riparian buffers; restoring 500 ha of native corridors; mandating 20% urban tree canopy cover; and establishing community-based green space monitoring. The findings provide empirical insights into sustainability challenges facing mid-sized African cities and offer transferable strategies for ecologically sensitive urban planning.

Lokoja, the capital of Kogi State, Nigeria, is a rapidly growing mid-sized city located at the confluence of the Niger and Benue Rivers. While this location has driven urban expansion, it has simultaneously increased the city’s exposure to environmental risks, particularly flooding and ecosystem degradation. Despite their growing importance, cities of this scale remain underrepresented in African urban research. Using multi-decadal Landsat imagery (2000, 2010, 2020, and 2024), Random Forest supervised classification, and PyLandStats landscape metrics, this study examines the spatio-temporal dynamics of urban growth and landscape fragmentation in Lokoja. Results reveal a non-linear urban trajectory characterized by rapid expansion (2000–2010), partial consolidation (2010–2020), and renewed densification with intensified fragmentation (2020–2024). Urban land cover expanded from 6,668 ha in 2000 to 19,371 ha in 2010, declined to 12,883 ha in 2020, and increased again to 15,985 ha by 2024, representing a net growth of approximately 140%. Urban expansion has imposed severe ecological costs. Dense forest cover declined by 99.7% (from 373 ha to 1 ha), while woodland areas were reduced by 73.9%. Core habitat declined from 23% to 13.8% of the landscape, falling below the 15–20% threshold associated with ecological functionality. Edge density increased by 121%, amplifying urban heat island effects, surface runoff, and biodiversity loss. Although grassland cover increased by 77.1%, this reflects secondary succession rather than ecological recovery, given an estimated loss of 3,000 ha of original vegetation. The study recommends enforcing development restrictions below 10 m elevation with 100 m riparian buffers, restoring 500 ha of native riparian corridors, mandating a minimum of 20% urban tree canopy cover, and institutionalizing community-based monitoring of green spaces. These findings contribute empirical evidence on the sustainability challenges of mid-sized African cities and offer transferable planning strategies for ecologically sensitive urban regions.