Abstract
Presently, the urban heat island (UHI) phenomenon, and its adverse impacts, are becoming major research foci in various interrelated fields due to rapid changes in urban ecological environments. Various cities have been investigated in previous studies, and most of the findings have facilitated the introduction of proper mitigation measures to overcome the negative impact of UHI. At present, most of the mountain cities of the world have undergone rapid urban development, and this has resulted in the increasing surface UHI (SUHI) phenomenon. Hence, this study focuses on quantifying SUHI in Kandy City, the world heritage tropical mountain city of Sri Lanka, using Landsat data (1996 and 2017) based on the mean land surface temperature (LST), the difference between the fraction of impervious surfaces (IS), and the fraction of green space (GS). Additionally, we examined the relationship of LST to the green space/impervious surface fraction ratio (GS/IS fraction ratio) and the magnitude of the GS/IS fraction ratio. The SUHI intensity (SUHII) was calculated based on the temperature difference between main land use/cover categories and the temperature difference between urban-rural zones. We demarcated the rural zone based on the fraction of IS recorded, <10%, along with the urban-rural gradient zone. The result shows a SUHII increase from 3.9 °C in 1996 to 6.2 °C in 2017 along the urban-rural gradient between the urban and rural zones (10 < IS). These results relate to the rapid urban expansion of the study areas from 1996 to 2017. Most of the natural surfaces have changed to impervious surfaces, causing an increase of SUHI in Kandy City. The mean LST has a positive relationship with the fraction of IS and a negative relationship with the fraction of GS. Additionally, the GS/IS fraction ratio shows a rapid decline. Thus, the findings of this study can be considered as a proxy indicator for introducing proper landscape and urban planning for the World Heritage tropical mountain city of Kandy in Sri Lanka.
Highlights
Urban heat island (UHI), a phenomenon of higher air and surface temperatures occurring in urban and suburban areas, has been examined in comparison with neighbouring rural areas [1,2]
This study aims to provide a better understanding of surface UHI (SUHI) formation in a tropical mountain city by using several variables, such as the fractions of impervious surfaces and green surfaces, and to create a green space impervious surface fraction ratio
This study shows that Kandy City and the surrounding areas were affected by the formation of SUHIs from 1996 to 2017
Summary
Urban heat island (UHI), a phenomenon of higher air and surface temperatures occurring in urban and suburban areas, has been examined in comparison with neighbouring rural areas [1,2]. The formation of SUHI is one of the significant negative phenomena because it is a by-product of rapid urbanization [7]. This rapid urban growth has caused a decrease in urban green areas when they are converted to impervious surfaces (roads, parking lots, buildings, and other constructions) [8]. Green spaces can control the SUHI by providing cooling effects through evapotranspiration [2]. The fractions of impervious surfaces and green spaces are important for the study of the formation of SUHI [7,9,10,11]
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