Assessment of heat index variability and urban heat island dynamics across Abeokuta and Shagamu, Southwestern Nigeria

Southwestern Nigeria is undergoing rapid land-use change that is intensifying urban warming, yet empirical evidence remains limited for cities such as Abeokuta and Shagamu. This study assessed heat conditions by analysing Heat Index (HI) values derived from temperature and relative humidity measured at sixteen sites between February 2020 and March 2021 using digital temperature–humidity loggers. Sites were classified as urban or rural through field observations and validated using remote-sensing land cover analysis within a 1 km buffer. Pearson correlation and principal component analysis (PCA) of HI against ERA5-Land meteorological variables (net and downward solar and thermal radiation, and total cloud cover) were used to quantify the meteorological correlates of Urban Heat Island (UHI)-related HI variability, complementing polynomial regression used to characterise seasonal HI trends. Heat patterns varied with temperature–humidity interactions, with polynomial models explaining over 60% of the seasonal variability (R² > 0.6), while solar radiation and cloud cover were the dominant statistical correlates of HI, jointly accounting for more than 95% of the variance among meteorological predictors. Urban sites consistently recorded higher HI than rural sites, with the highest HI (45.0 °C; danger category) occurring at a site with a completely built-up 1 km buffer, and Shagamu consistently experienced greater heat stress than Abeokuta. An exploratory, absolute-threshold assessment (daily mean HI ≥ 32 °C for ≥ 3 consecutive days) found no qualifying heat wave events during the monitoring period; given the well-documented limitations of fixed absolute thresholds in tropical climates, which do not account for acclimatization, this result is reported as a secondary observation rather than a core finding, with the manuscript’s central focus remaining HI variability and urban heat dynamics. These findings highlight the combined influence of urban morphology and meteorological conditions on heat stress and provide evidence to support climate-responsive urban planning and heat-risk mitigation in Southwestern Nigeria.