Quantifying Surface Urban Heat Island Formation in the World Heritage Tropical Mountain City of Sri Lanka

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.

Landscape Changes and their Impacts on Land Surface Temperature in Tropical Hill Stations in South Asia: A Case Study of Nuwara Eliya, Sri Lanka

“…Rapid changes in the landscape have resulted in the conversion of natural vegetation and agricultural land into built-up (impervious) land, such as buildings, parking lots, roads, and other constructions [1][2][3][4]. This has caused several environmental problems at local, regional, and global scales [5], such as decreases in agricultural land [6]; habitat destruction [5,7,8]; air, soil, and water contamination [9,10]; increases in vector-borne diseases, such as malaria and dengue [11]; decreases in green space [12,13]; and increases Land Surface Temperature (LST) [14][15][16].…”

“…Many urban landscapes from small to large scales have been studied worldwide [15,34,35], including coastal cities [15,32,36,37], desert cities [19,38], and mountain cities [12,13]. Mountain cities are attractive for rich people as they have a cold climate and comfortable living conditions, which have resulted in rapid urban development [13].…”

“…The spatial distribution of the LST intensity (LSTI) provides essential environmental information for understanding the temperature pattern in detail. Two methods can be used to study LSTI, such as (1) categorization of land use and cover as the local climate zone and following the cross cover comparison method used to calculate the LSTI [12,13,[41][42][43], and (2) determining the difference in the mean LST between urban and rural zones based on the urban-rural gradient analysis. The mean LST, a fraction of built-up land (BL), and green spaces have been used in previous studies [12,13].…”

“…The urban-rural demarcation is essential for determining the temperature difference. In this study, we calculated the gradient zone as the <10% fraction of BL from the city center [12,13]. The AL was considered as a part of green spaces in most of the previous studies [12,13].…”

“…In this study, we calculated the gradient zone as the <10% fraction of BL from the city center [12,13]. The AL was considered as a part of green spaces in most of the previous studies [12,13]. However, we used a separate fraction of AL to understand the LSTI by considering the spatial distribution in Nuwara Eliya.…”