Vegetation, Built-up Intensity and Land Surface Temperature: A Multi-Temporal Analysis of Urban Change in Ilorin, Nigeria

Abstract

Rapid urbanisation alters vegetation cover, built-up intensity, and surface thermal conditions; however, these relationships may change as urban landscapes evolve. This study examines the spatio-temporal relationships among the Normalised Difference Vegetation Index (NDVI), Normalised Difference Built-up Index (NDBI), and Land Surface Temperature (LST) in Ilorin Metropolis, Nigeria, using Landsat observations from 2005, 2015, and 2025. Landsat Collection 2 Level-2 imagery was processed in Google Earth Engine to derive NDVI, NDBI, and LST, followed by spatial overlay and simple linear regression to evaluate their relationships. The results indicate substantial urban surface transformation, with built-up land increasing from 7,007.87 ha (3.57%) in 2005 to 28,981.44 ha (14.76%) in 2025. Mean NDVI ranged from 0.327 in 2005 to 0.386 in 2015 and returned to 0.327 in 2025, while mean NDBI increased from 0.039 to 0.091. Mean LST rose progressively from 38.34°C in 2005 to 39.58°C in 2015 and 40.64°C in 2025, representing an overall increase of 2.30°C. NDVI demonstrated negative associations with LST, with R² values of 0.3149, 0.4647, and 0.0966, whereas NDBI exhibited positive associations with R² values of 0.4298, 0.4314, and 0.2409 for the respective years. The declining explanatory power of both indices by 2025 suggests increasing complexity in the urban thermal environment. These findings underscore the value of multi-temporal Earth observation for monitoring urban thermal change and highlight the importance of vegetation conservation and impervious-surface management as key elements of climate-sensitive urban planning.