Assessing the status of ecosystem regulating services in the urbanising Rainforest and Guinea savanna ecological regions of Nigeria using InVEST models

Maintaining an equilibrium between the rapid pace of urbanisation and the demand for urban ecological well-being amid climate change remains a global challenge. This study integrates machine learning and geospatial techniques with biophysical models to investigate the changes in ecosystem regulating services (ERS), such as carbon stock and climate regulation, in cities of the Rainforest (Akure and Owerri) and Guinea savanna (Makurdi and Minna) ecological regions of Nigeria in 2002 and 2022. Landsat images were processed using the random forest (RF) machine learning classifier, with the Normalised Difference Vegetation Index (NDVI) and Land Surface Temperature (LST) serving as indicators of landscape changes. The Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) platform was deployed to assess carbon storage and sequestration, and cooling and heat mitigation (HMI) services. Urban and agricultural expansion was associated with a drastic depletion of ERS within a 5 km–10 km radius of the urban core, resulting in an 8.60 %–33.83 % decline in carbon stock and a 5 %–13 % decline in HMI across cities. Correlation and geographically weighted regression models revealed that in the Rainforest (Akure and Owerri), carbon sequestration and heat mitigation are more influenced by LST, with strong correlations in Akure (r = 0.499) and Owerri (r = 0.408). In the Guinea savanna, carbon sequestration pattern in Makurdi is influenced by LST (r = 0.419), while Minna shows a stronger influence of NDVI on both carbon stock and heat mitigation. This highlights the influence of urbanisation and ecological variations in providing urban ERS and underscores the importance of enhancing vegetation biomass through existing urban and rural afforestation frameworks and sustainable agricultural practices. These measures are crucial for improving carbon stock, enhancing the heat mitigation potential of urban areas, and mitigating the impacts of further climate change.