Vegetation and Radiative Controls on Urban Heat Islands in Lagos Metropolis, Nigeria (1984–2013): A PCA Approach

Urbanization modifies the surface energy balance and drives Urban Heat Island (UHI) intensification, yet the quantitative partitioning of radiative, thermal, and vegetation controls remains poorly constrained in rapidly growing tropical megacities. This study quantified spatiotemporal dynamics of Land Surface Temperature (LST), Net Radiation (Rn), Normalized Difference Vegetation Index (NDVI), and urban built-up extent in Lagos metropolis, Nigeria, from 1984 to 2013, and identified latent climatic controls using Principal Component Analysis (PCA) with Varimax rotation. Landsat Thematic Mapper (TM) 5, Enhanced Thematic Mapper Plus (ETM+) 7, and Operational Land Imager (OLI) 8 imagery were processed to retrieve LST via single-channel algorithms, Rn from surface energy balance components, and NDVI from red and near-infrared reflectance. Four variables—urban built-up fraction, LST, Rn, and NDVI—were subjected to PCA. Mean LST in built-up zones increased from 24.76°C in 1984 to 28.59°C in 2013, while NDVI and rural open land declined by 68%. PCA extracted two orthogonal factors accounting for 100.00% of cumulative variance. Factor 1, termed the Radiative-Thermal Factor, exhibited loadings of 0.999 for LST, 0.998 for Rn, and 0.764 for urban built-up fraction, explaining 67.89% of variance. Factor 2, the Vegetation Factor, loaded 0.998 on NDVI and explained 32.11% of variance. The urban–rural LST differential widened from 2.69°C to 4.87°C, and daytime Surface UHI extent expanded from 147.06 km² to 332.36 km². Results indicate that urbanization-induced alterations in radiative balance and vegetation loss constitute the principal controls on Lagos’s urban climate. Mitigation should prioritize expansion of green infrastructure, deployment of high-albedo materials, and mandatory UHI impact assessment in high-priority Local Government Areas.