Abstract
Urban growth and its associated expansion of built-up areas are expected to continue through to the twenty second century and at a faster pace in developing countries. This has the potential to increase thermal discomfort and heat-related distress. There is thus a need to monitor growth patterns, especially in resource constrained countries such as Africa, where few studies have so far been conducted. In view of this, this study compares urban growth and temperature response patterns in Freetown and Bo town in Sierra Leone. Multispectral Landsat images obtained in 1998, 2000, 2007, and 2015 are used to quantify growth and land surface temperature responses. The contribution index (CI) is used to explain how changes per land use and land cover class (LULC) contributed to average city surface temperatures. The population size of Freetown was about eight times greater than in Bo town. Landsat data mapped urban growth patterns with a high accuracy (Overall Accuracy > 80%) for both cities. Significant changes in LULC were noted in Freetown, characterized by a 114 km2 decrease in agriculture area, 23 km2 increase in dense vegetation, and 77 km2 increase in built-up area. Between 1998 and 2015, built-up area increased by 16 km2, while dense vegetation area decreased by 14 km2 in Bo town. Average surface temperature increased from 23.7 to 25.5 °C in Freetown and from 24.9 to 28.2 °C in Bo town during the same period. Despite the larger population size and greater built-up extent, as well as expansion rate, Freetown was 2 °C cooler than Bo town in all periods. The low temperatures are attributed to proximity to sea and the very large proportion of vegetation surrounding the city. Even close to the sea and abundant vegetation, the built-up area had an elevated temperature compared to the surroundings. The findings are important for formulating heat mitigation strategies for both inland and coastal cities in developing countries.
Highlights
There has been an increase in the number of urban dwellers, together with an accompanying expansion of built-up area globally [1]
We have compared urban growth and land surface temperature patterns between a coastal city (Freetown) and an inland city (Bo town) in Sierra Leone in this paper
Based on the findings of the study, we conclude that multi-spectral Landsat data and the Support Vector Machine algorithm retrieve land use and land cover (LULC) spatial patterns and urban growth with a high accuracy
Summary
There has been an increase in the number of urban dwellers, together with an accompanying expansion of built-up area globally [1]. Urban areas are strategic areas economically, as well as from an administrative perspective They are important for issues such as the improvement of education and health delivery of a nation. Despite their socio-economic importance, urban areas and characteristic complex land use and land cover (LULC) spatial structure pose a variety of environmental changes [2,3,4,5]. The challenges, include air pollution and water pollution in industrialized areas, while flash flooding is prevalent in highly impervious areas Another notable challenge of urban development is temperature elevation, especially in densely built-up areas [6,7]. It is important to establish city specific land surface temperature patterns in order to derive relevant mitigation and response strategies
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