Mechanistic Modelling of Urban Heat Island Mitigation Through Green Infrastructure in Lagos: A Climate-Hydrology-Energy Coupled Approach

This dissertation develops a mechanistic coupled climate-hydrology-energy modelling framework for quantifying urban heat island mitigation by green infrastructure interventions in Lagos, South West Nigeria, making original contributions to urban microclimate modelling science under tropical megacity conditions. Lagos experiences intense urban heat island effects driven by rapid expansion of impervious surfaces and loss of urban tree cover, with documented increases in urban heat exposure that exacerbate outdoor worker heat stress, increase building cooling energy demand, and intensify stormwater runoff. Quantifying the cooling benefits of specific green infrastructure configurations including urban forests, green roofs, and vegetated swales requires coupled modelling that integrates urban surface energy balance, vegetation transpiration dynamics, soil water balance, and boundary layer atmospheric dynamics in a way that existing urban climate models, developed for temperate city conditions, do not adequately achieve for tropical humid conditions. The theoretical contribution is a Tropical Urban Microclimate Model that adapts the SUEWS urban surface energy balance model for the specific canopy resistance parameterisation of tropical tree species, incorporates a dual-source evapotranspiration representation for green roof substrates under tropical soil moisture dynamics, and couples the surface energy model with a diagnostic urban boundary layer formulation validated for West African atmospheric conditions. Model validation uses a newly assembled dataset of urban flux measurements from three eddy covariance towers installed in Lagos for this research. Simulation scenarios evaluate the cooling effect of urban forest expansion, green roof retrofit at scale, and corridor greening on land surface temperature, outdoor thermal comfort, and building energy demand. Keywords: urban heat island, green infrastructure, tropical microclimate, Lagos, energy balance modelling.