Dynamics of land cover, land surface temperature and NDVI in Uyo City, Nigeria

Abstract

Uyo City in Akwa Ibom State, Nigeria has experienced rapid urban growth and development over the past decades. The urban expansion has led to different land cover transitions which in turn have caused significant changes in key environmental parameters such as Land Surface Temperature (LST) and Normalised Difference Vegetation Index (NDVI). This study investigated land cover changes in Uyo and the relationship with LST and NDVI. Landsat multispectral imageries covering the study area were acquired for three periods – 1986, 2000 and 2018. Land cover was extracted using the Maximum Likelihood Classification (MLC) technique, LST was derived using a single channel algorithm applied on the imagery thermal bands, and the NDVI equation was applied to the imageries. To assess the MLC accuracy, four different accuracy metrics were calculated – user's accuracy, producer's accuracy, overall accuracy, and kappa coefficient. Change statistics were computed to evaluate the transition dynamics of each land cover class. Finally, the relationship between land cover, LST and NDVI was evaluated using the Contribution Index (CI) and Pearson's Correlation analysis. Between 1986 and 2018, vegetation declined from 278 km2 to 219 km2, wetlands declined from 20 km2 to 17 km2, barren land declined from 33km2 to 25km2 while built-up areas increased from 69 km2 to 139 km2. There were significant transitions in land cover for instance, 78km2 of vegetation and 14km2 of barren land were converted to built-up area over the 32 years. The mean LSTs in the city were 21.67 °C (1986), 25.40 °C (2000) and 26.04 °C (2018). The highest contribution to LST was from built-up areas while the lowest was from vegetation. The CI of built-up areas rose from 0.08 in 1986 to 0.30 in 2018, Similarly, LST profiles showed that the diffusion of higher LSTs across the study area was in tandem with the horizontal expansion of built-up areas. There was also a high negative correlation between LST and NDVI at the three periods of study. It is recommended that the Uyo local authorities take deliberate measures and policies aimed at moderating urban growth while ensuring the conservation of urban greens spaces in the city.