Quantitative assessment of the relationship between land use/land cover (LULC), topographic elevation and land surface temperature (LST) in Ilorin, Nigeria

Abstract

The urbanization of landscapes and the increase in impervious land cover materials is known to cause significant changes in the landscape's thermal properties, typically leading to urban heat island (UHI). Although previous studies have investigated the impacts of land cover land use (LULC) and other factors on the urban land surface temperature (LST), the results of such studies are mixed. For instance, it is not yet clear what factors affect the spatial and temporal variation of the relationship between LULC and the LST, as well as the exact trajectory through which identified factors affect the thermal character of the urban landscape. In the current study, we examined the relationship between LULC, elevation and LST in Ilorin from the period of 2002–2020. The overriding aim was to understand the degree of association between LULC, elevation and LST, and the drivers of the spatial and temporal variation in the observed relationship. LST and NDVI were derived from Landsat data products. LST was derived using a mono-window algorithm and NDVI was used as proxy for LULC. The spatial pattern of LULC was analyzed using Moran's I spatial autocorrelation statistics. To investigate the relationship between LULC, elevation and LST, we adopted both ordinary least square (OLS) regression models and the geographically weighted regression (GWR) method to reveal both the linear and the geographically varying relationship between the LULC, elevation and LST. The results of the study show that the LULC pattern of Ilorin has been significantly altered during the 2000 to 2020 period. The urban proportion of the landscape has shown a significant increase, rising by more than 11% relative to 2002 figures, and the vegetation proportion, especially the forest component, has diminished within same temporal extent. LST values varied in both space and time, with high temperature clusters noticeable in the built-up areas and decreasing towards the urban periphery. The result of the autocorrelation analysis using Moran's I index reveals a significant clustering of LST in all the epochs investigated. Across the study area, minimum and maximum LST values of 0 °C and 41 °C were recorded in 2002 and 2020 respectively. Statistically significant relationships were observed between LULC, elevation and LST. However, the relationship between elevation and LST was very weak. Temporally, the strength of the relationship between the variables (as indicated in the variables' coefficient) as well as the overall model predictive performance (indicated by in the R2) fluctuated over the years. Spatially, the strength of relationship between LST and LULC and elevation varied significantly. LULC explained approximately between 26% and 64% of total LST variation in the city between 2002 and 2020. The study findings are relevant for efforts geared towards alleviating the degree of UHI or its impacts, generally, and in the city of Ilorin, in particular. An understanding of the spatial distribution of LULC and their impacts on the LST can be helpful in identifying areas needing attention. The observed relationship between relevant LULC classes can be incorporated into urban planning strategies to ensure a sustainable city development.