Abstract
The Urban Heat Island (UHI) is a metropolis whose temperature is several degrees higher than the surrounding rural areas. In connection with the UHI phenomenon, the earth’s surface temperature (LST) was estimated using Landsat satellite imagery covering the city of Colombo. The results showed that the UHI effect spread to the north, east, and southeast of Colombo City between 2001 and 2019. Analyzing the correlation between the LST, normalized vegetation difference index (NDVI) and normalized difference index (NDBI), it is found that there is an inverse correlation between NDVI and LST; however, it is reported that NDBI is associated with the four LST periods of 2001, 2009, 2016 and 2019 which indicates that vegetation can weaken UHI, while built-up land can enhance the UHI. The result of albedo analysis shows that low albedo has a greater impact on the formation of UHI. According to this environmental assessment using the Urban Thermal Difference Index (UTFVI), 27% of the region suffers the worst thermal stress. Therefore, in future urban planning, mitigation measures should be taken to improve the quality of the life of the people and the environment in the city of Colombo.
Highlights
After the industrial revolution, globalization and the migration of countries to cities are driving urbanization
Since simultaneous Land Surface Temperature data were not available when the satellite passes the area, daily average air temperature measurements recorded by Department of Meteorology were used to verify the final retrieved LST results obtained from this study (Table 3)
normalized vegetation difference index (NDVI) vs LST and Normalized Difference Built-up Index (NDBI) vs LST in this study shown in the Figure 6 and regression analysis conducted LST vs NDVI and LST vs NDBI with correlation coefficients are given in the Table 5
Summary
Globalization and the migration of countries to cities are driving urbanization. In 2015-2020, 2020-2025 and 20252030, the world urban population expect to grow by 1.84%, 1.63% and 1.44% each year [2] It is a common characteristic of urban areas having single use zoning, roads and bridges, low density residential housing, government administrative buildings, private and public sector trading and commercial buildings, airport and harbours, warehouses, various industries, public and private transportation, leading to rapid land use pattern changes [3]. These urban areas tend to have high, thermal conductivity and throughput in addition to the solar energy absorption, because most structures (such as streets, sidewalks, parking lots, roofs and darker-surfaced buildings) have used construction materials with low reflectivity.
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