Exploring the Cooling Effects of Urban Wetlands in Colombo City, Sri Lanka
An urban heat island (UHI) refers to urban areas that experience higher temperatures due to heat absorption and retention by impervious surfaces compared to the surrounding rural areas. Urban wetlands are crucial in mitigating the UHI effect and improving climate resilience via their cooling effect....
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MDPI AG
2025-05-01
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| author | Darshana Athukorala Yuji Murayama N. S. K. Herath C. M. Madduma Bandara Rajeev Kumar Singh S. L. J. Fernando |
| author_facet | Darshana Athukorala Yuji Murayama N. S. K. Herath C. M. Madduma Bandara Rajeev Kumar Singh S. L. J. Fernando |
| author_sort | Darshana Athukorala |
| collection | DOAJ |
| description | An urban heat island (UHI) refers to urban areas that experience higher temperatures due to heat absorption and retention by impervious surfaces compared to the surrounding rural areas. Urban wetlands are crucial in mitigating the UHI effect and improving climate resilience via their cooling effect. This study examines Colombo, Sri Lanka, the RAMSAR-accredited wetland city in South Asia, to assess the cooling effect of urban wetlands based on 2023 dry season data for effective sustainable management. We used Landsat 8 and 9 data to create Land Use/Cover (LUC), Land Surface Temperature (LST), and surface-reflectance-based maps using the Google Earth Engine (GEE). The Enhanced Vegetation Index (EVI), Modified Normalized Difference Water Index (mNDWI), topographic wetness, elevation, slope, and impervious surface percentage were identified as the influencing variables. The results show that urban wetlands in Colombo face tremendous pressure due to rapid urban expansion. The cooling intensity positively correlates with wetland size. The threshold value of efficiency (TVoE) of urban wetlands in Colombo was 1.42 ha. Larger and more connected wetlands showed higher cooling effects. Vegetation- and water-based wetlands play an important role in <10 km urban areas, while more complex shape configuration wetlands provide better cooling effects in urban and peri-urban areas due to edge effects. Urban planners should prioritize protecting wetland areas and ensuring hydrological connectivity and interconnected wetland clusters to maximize the cooling effect and sustain ecosystem services in rapidly urbanizing coastal cities. |
| format | Article |
| id | doaj-art-ee46ef2b43cf456eaa6b1b3c9e6a0b4a |
| institution | DOAJ |
| issn | 2072-4292 |
| language | English |
| publishDate | 2025-05-01 |
| publisher | MDPI AG |
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| series | Remote Sensing |
| spelling | doaj-art-ee46ef2b43cf456eaa6b1b3c9e6a0b4a2025-08-20T03:11:20ZengMDPI AGRemote Sensing2072-42922025-05-011711191910.3390/rs17111919Exploring the Cooling Effects of Urban Wetlands in Colombo City, Sri LankaDarshana Athukorala0Yuji Murayama1N. S. K. Herath2C. M. Madduma Bandara3Rajeev Kumar Singh4S. L. J. Fernando5Institute of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8572, JapanInstitute of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8572, JapanDepartment of Environmental Management, Rajarata University of Sri Lanka, Mihintale 50300, Sri LankaDepartment of Geography, University of Peradeniya, Peradeniya 20400, Sri LankaDepartment of International Relations, Kobe City University of Foreign Studies, 9 Chome-1, Gakuen Higashimachi, Nishi-ku, Kobe-shi 651-2187, JapanDepartment of Geography, Faculty of Humanities and Social Sciences, University of Ruhuna, Matara 81000, Sri LankaAn urban heat island (UHI) refers to urban areas that experience higher temperatures due to heat absorption and retention by impervious surfaces compared to the surrounding rural areas. Urban wetlands are crucial in mitigating the UHI effect and improving climate resilience via their cooling effect. This study examines Colombo, Sri Lanka, the RAMSAR-accredited wetland city in South Asia, to assess the cooling effect of urban wetlands based on 2023 dry season data for effective sustainable management. We used Landsat 8 and 9 data to create Land Use/Cover (LUC), Land Surface Temperature (LST), and surface-reflectance-based maps using the Google Earth Engine (GEE). The Enhanced Vegetation Index (EVI), Modified Normalized Difference Water Index (mNDWI), topographic wetness, elevation, slope, and impervious surface percentage were identified as the influencing variables. The results show that urban wetlands in Colombo face tremendous pressure due to rapid urban expansion. The cooling intensity positively correlates with wetland size. The threshold value of efficiency (TVoE) of urban wetlands in Colombo was 1.42 ha. Larger and more connected wetlands showed higher cooling effects. Vegetation- and water-based wetlands play an important role in <10 km urban areas, while more complex shape configuration wetlands provide better cooling effects in urban and peri-urban areas due to edge effects. Urban planners should prioritize protecting wetland areas and ensuring hydrological connectivity and interconnected wetland clusters to maximize the cooling effect and sustain ecosystem services in rapidly urbanizing coastal cities.https://www.mdpi.com/2072-4292/17/11/1919urban wetlandscooling effecturbanizationLSTcoastal citiesColombo |
| spellingShingle | Darshana Athukorala Yuji Murayama N. S. K. Herath C. M. Madduma Bandara Rajeev Kumar Singh S. L. J. Fernando Exploring the Cooling Effects of Urban Wetlands in Colombo City, Sri Lanka Remote Sensing urban wetlands cooling effect urbanization LST coastal cities Colombo |
| title | Exploring the Cooling Effects of Urban Wetlands in Colombo City, Sri Lanka |
| title_full | Exploring the Cooling Effects of Urban Wetlands in Colombo City, Sri Lanka |
| title_fullStr | Exploring the Cooling Effects of Urban Wetlands in Colombo City, Sri Lanka |
| title_full_unstemmed | Exploring the Cooling Effects of Urban Wetlands in Colombo City, Sri Lanka |
| title_short | Exploring the Cooling Effects of Urban Wetlands in Colombo City, Sri Lanka |
| title_sort | exploring the cooling effects of urban wetlands in colombo city sri lanka |
| topic | urban wetlands cooling effect urbanization LST coastal cities Colombo |
| url | https://www.mdpi.com/2072-4292/17/11/1919 |
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