Spatial Changes of Urban Heat Island Formation in the Colombo District, Sri Lanka: Implications for Sustainability Planning

Abstract

The formation of surface urban heat islands (SUHIs) can cause significant adverse impacts on the quality of living in urban areas. Monitoring the spatial patterns and trajectories of UHI formations could be helpful to urban planners in crafting appropriate mitigation and adaptation measures. This study examined the spatial pattern of SUHI formation in the Colombo District (Sri Lanka), based on land surface temperature (LST), a normalized difference vegetation index (NDVI), a normalized difference built-up index (NDBI), and population density (PD) using a geospatial-based hot and cold spot analysis tool. Here, 'hot spots' refers to areas with significant spatial clustering of high variable values, while 'cold spots' refers to areas with significant spatial clustering of low variable values. The results indicated that between 1997 and 2017, 32.7% of the 557 divisions in the Colombo District persisted as hot spots. These hot spots were characterized by a significant clustering of high composite index values resulting from the four variables (LST, NDVI (inverted), NDBI, and PD). This study also identified newly emerging hot spots, which accounted for 49 divisions (8.8%). Large clusters of hot spots between both time points were found on the western side of the district, while cold spots were found on the eastern side of the district. The areas identified as hot spots are the more urbanized parts of the district. The emerging hot spots were in areas that had undergone landscape changes due to urbanization. Such areas are found between the persistent hot spots (western parts of the district) and persistent cold spots (eastern parts of the district). Generally, the spatial pattern of the emerging hot spots followed the pattern of urbanization in the district, which had been expanding from west to east. Overall, the findings of this study could be used as a reference in the context of sustainable landscape and urban planning for the Colombo District.

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

“…Concerning 1996 and 2006, only zones 1 and 2 indicated the GS/IS fraction ratio of less than 1. However, in 2017, it shifted to a 2.7 km distance from the city centre (URZ 13 ). This shows IS areas were increasing toward the periphery areas from the city centre.…”

“…Prior to providing policies to enhance the green cover of the city, it is important to protect every single tree currently existing. The policy needs to be more focused on protecting remaining green areas inside Kandy City, as well as building with green roofs, green buildings, urban agriculture, green parks, and tree planting along the main roads and government buildings [7,8,11,13], which will help to improve the GS/IS fraction ratio of the city.…”

“…The acquisition time of the three satellite images might have an influence on the result. In addition to that, several environmental factors such as wind speed, surface moisture, humidity, and intensity of solar radiation could influence the LST during the different years [7,13]. However, this study used relative LST difference over the three years, rather than the absolute temperature.…”

“…Thus, it is vital to understand the SUHI formation in order to introduce proper mitigation measures. Formerly, most SUHI studies focused on various types of cities, such as tropical coastal cities [11,13,14], desert cities [9,15], and mountain cities [7]. Hence, studies regarding the SUHI formation in mountain cities are becoming important for identifying the rapid changing patterns of the thermal environment.…”

“…Most previous SUHI studies in Sri Lanka have focused on the Colombo area, the commercial capital of the country [8,13,28]. However, SUHI studies are lacking in Kandy City.…”