Decarbonisation Potential of Nigerian Cities Through Urban Green Infrastructure: A Geospatial Carbon Sequestration Modelling Approach

Urban green infrastructure has been identified as a potentially significant, cost-effective contribution to municipal climate change mitigation and adaptation, yet quantitative assessment of the carbon sequestration potential of urban vegetation across Nigerian cities and the spatial prioritisation of greening investments have not been investigated at the national scale. This dissertation develops an original geospatial carbon sequestration modelling approach to quantify existing urban vegetation carbon stocks and model the decarbonisation potential of urban green infrastructure expansion scenarios across Nigeria's twelve largest cities. High-resolution tree canopy cover mapping is conducted using a deep learning semantic segmentation model trained on 0.5-metre WorldView-3 imagery with manually delineated reference polygons covering 240 square kilometres across six cities representing Nigeria's climate zones. Above-ground urban tree biomass is estimated from canopy cover density using allometric scaling relationships derived from field-measured tree parameters at 480 sample plots in urban green spaces across the study cities. Current urban tree carbon stocks are estimated at 2.3 million tonnes CO2-equivalent across the twelve cities combined. Three green infrastructure expansion scenarios for 2035 are modelled: targeted street tree planting, park densification, and building-integrated vegetation, with total sequestration potential and cooling co-benefits estimated for each. An original Urban Green Carbon Priority Index is developed to rank sub-district investment zones by combined sequestration potential, heat risk reduction, and implementation feasibility. The dissertation provides city-specific green infrastructure investment roadmaps for Nigeria's Nationally Determined Contribution urban component. Keywords: urban green infrastructure, carbon sequestration, geospatial modelling, Nigerian cities, climate mitigation.