Quantitative study on the cooling effect of green roofs in a high-density urban Area—A case study of Xiamen, China

Abstract

Green roofs are thought to be an effective measure to solve the contradiction between land shortages and ecological construction, especially address urban heat island (UHI) effects in high-density urban areas. However, few empirical studies have focused on the cooling effect of green roof projects at urban scales. This study quantified the cooling effect of green roofs in Xiamen Island, China, where 540,000 m2 of green roofs were implemented between 2015 and 2017, in order to address the two research questions: (1) do green roofs in high-density urban areas have a significant cooling effect at the city scale and (2) what is the extent of the cooling? The relative difference between the average land surface temperature (LST) of Xiamen Island and the green roofs stemmed from Landsat 8 remote sensing image in the summers of 2014 and 2017 were calculated in geographic information systems (GIS) to represent the cooling effect of green roof project. Results showed that: (1) the average LST difference between green roofs and Xiamen Island decreased by 0.91 °C, indicating that green roofs could effectively alleviate UHI effects in high-density urban areas; (2) The cooling effect was significant up to 100 m from the green roof installation in Xiamen Island, we called it as characteristic cooling buffer zone; (3) Regression analysis revealed that for every 1000 m2 increase in green roof area, the average LST of the roof and its characteristic cooling buffer zone decreased by 0.4 °C. These findings provide the empirical proof for the cooling effect of green roofs on the surrounding environment in high-density urban areas and important insights for urban planners and government agencies for the effective mitigation of UHI impacts.