Assessment of Urban Growth Effect on the Formation and Intensification of Urban Heat Islands in Sekondi-Takoradi Metropolis of Ghana

Abstract

The prevalence of industries as well as the presence of the harbour and airport, and the upsurge in economic activities due to the oil discovery have made Sekondi-Takoradi one of the preferred cities for many people and migrants. As a result, the number of urban dwellers has increased, and this by effect, has been met by an increasing transformation of the land use land cover (LULC) into built-up, sprawl-like growth and a direct influence on temperature rise. Previous studies have not established enough evidence on land use and land cover changes in the metropolis and the influence of urban growth on the development of urban heat islands (UHIs) in the metropolis remains understudied. For this reason, this study assessed the effect of urban growth on the formation and intensification of urban heat islands in Sekondi-Takoradi. Multi-source datasets such as remote sensing data (Landsat images), referenced data, and vector data served as the basis for evaluating the spatiotemporal dynamics of land use and land cover, urban sprawl, and urban heat island within the metropolis. The supervised random forest technique was utilized to map the land cover changes whereas Geospatial techniques and spatial metrics such as Annual Urban Expansion Rate (AEUR), Urban Expansion Intensity Index (UEII), Landscape metrics, Shannon, and relative entropy were used to evaluate the spatio-temporal pattern of urban growth in the Sekondi-Takoradi metropolis. Furthermore, the spectral indices, elevation, some proximity factors, land surface temperature (LST), and urban thermal field variance index (UTFVI) were used to analyze the development of urban heat Islands and its intensification by urban growth or urban expansion as well as investigate temperature variations across the metropolis. Results from the changes in land use land cover showed a substantial increase in built-up by 63.08 km2 (32.91%) and a decrease in vegetation and water by 60.99 km2 (31.82%) and 2.08 km2 (1.09%) respectively. Projections for 2030 indicate further changes with water areas decreasing to 1.21 km2 (0.63 %), vegetation diminishing to 95.31 km2 (49.73 %), and built-up areas expanding to 95.14 km2 (49.64 %). This shows the rate at which the metropolis is becoming urbanized and raises concern about the adverse effects the metropolis may experience if urban expansion is not properly monitored and controlled. Also, the urban expansion analysis, specifically, the urban intensity index revealed that the metropolis expanded from a slow speed (0.34) to a very high speed (2.58), highlighting the high susceptibility of the area to experiencing urban sprawl. The presence of sprawling characteristics was confirmed throughout the application of landscape metrics which revealed a greater degree of fragmentation in the landscape. Additionally, the results from Shannon and iii relative entropy computations, which respectively ranged from 2.17 to 2.47 and 0.76 to 0.87 revealed that the metropolis has been sprawling throughout the study period and this would cause significant changes in the land cover composition of the metropolis and potentially impede the achievement of Sustainable Development Goal 11. Unfortunately, the effect of this dramatic land use change and urban sprawl led to a 3.1°C rise in mean LST and a 19.38 km2 expansion of areas affected by the UHI effect. The UTFVI analysis further indicated a 33.63 km2 increase in the worst ecological zone due to the temperature rise. Statistical analysis between LST, NDVI, NDWI, and NDBI revealed significant variability in explaining the intensity of LST and UHI in the metropolis over the study period. In addition to the spectral indices, elevation, and proximity factors significantly contributed to the temperature variation across the study area. Hence, provided valuable insight into the intensification of LST and UHI in the metropolis. This study equips city authorities and urban planners with the fundamental knowledge needed to prepare a sustainable development plan that alleviates adverse effects of urban growth and elevated temperature-related issues. Also, the findings contribute to global efforts to promote more livable and climate-resilient urban environments and highlight the significance of spatial modeling in environmental management and urban planning. Lastly, the combined use of remote sensing, GIS, and other supplementary datasets has proven to be efficient for evaluating the impact of urban growth on the formation and intensification of urban heat islands.