Abstract
One of the major impacts associated with unplanned rapid urban growth is the decrease of urban vegetation, which is often replaced with impervious surfaces such as buildings, parking lots, roads, and pavements. Consequently, as the percentage of impervious surfaces continues to increase at the expense of vegetation cover, surface urban heat island (SUHI) forms and becomes more intense. The Colombo Metropolitan Area (CMA), Sri Lanka, is one of the rapidly urbanizing metropolitan regions in South Asia. In this study, we examined the spatiotemporal variations of land surface temperature (LST) in the CMA in the context of the SUHI phenomenon using Landsat data. More specifically, we examined the relationship of LST with the normalized difference vegetation index (NDVI) and the normalized difference built-up index (NDBI) at three time points (1997, 2007 and 2017). In addition, we also identified environmentally critical areas based on LST and NDVI. We found significant correlations of LST with NDVI (negative) and NDBI (positive) (p < 0.001) across all three time points. Most of the environmentally critical areas are located in the central business district (CBD), near the harbor, across the coastal belt, and along the main transportation network. We recommend that those identified environmentally critical areas be considered in the future urban planning and landscape development of the city. Green spaces can help improve the environmental sustainability of the CMA.
Highlights
The United Nations (UN) has predicted that 66% of the global population will be living in urban areas by 2050 [1]
The significant correlations between land surface temperature (LST) and both normalized difference vegetation index (NDVI) and normalized difference built-up index (NDBI) (Figure 4) that we found in this study support this proposition and are consistent with other previous findings [10,25]
We examined the spatiotemporal patterns of LST in the Colombo Metropolitan Area (CMA) in the context of the surface urban heat island (SUHI) phenomenon using Landsat data (1997–2017)
Summary
The United Nations (UN) has predicted that 66% of the global population will be living in urban areas by 2050 [1]. In more developed regions such as Northern America, Latin America and the Caribbean, and Europe, 82%, 80% and 73% of their respective total populations are living in urban areas. In the developing regions of Asia and Africa, the proportion of their urban population is much lower, with about 48% and 40%, respectively [1]. According to a UN projection, the world’s urban population will increase by 2.5 billion people by 2050, and urbanization will be faster in Asia and Africa than in any other parts of the world. Their urban population will respectively increase to 64% and 56% by 2050 [1]. Other environmental consequences include environmental pollution, climate change, greenhouse gasses emissions, water and air quality deterioration and break down of ecological cycles [3,4]
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