Study on the Capacity of Extensive Green Roof to Mitigate Rainwater Runoff in Guangzhou

Abstract

Previous studies have shown that the extensive green roof (EGR) can serve to retain the rainwater and mitigate rainwater runoff, but most of studies were in the temperate zone. Located in the hot and rainy subtropical zone, Guangzhou(GZ) is one of China's earliest cities that promote vertical greening, yet the researches on the EGR in recent years focus more on the cooling effect, substrate screening and selection tests, than on the mitigation of rainwater runoff. For this study, three EGR test platforms were set up in GZ to test the EGRs with substrate thicknesses of 30mm, 50mm and 70mm in summer of higher concentration of rainfall events. The results showed that the rainwater retention performance of the 30mm, 50mm and 70mm-thick substrates were 23.29%, 27.20% and 28.44% respectively, and the mean peak reduction 18.94%, 26.17% and27.7%. Assume the EGR with 30mm-thick substrate is to be promoted throughout the 1,035.01 square kilometers built-up area in GZ, and the roof area accounts for about 37.25% of the built-up area, a total of 122.30million cubic meters of rainwater will then be retained during the period from May to August. This would largely help mitigate the urban waterlogging and ease the pressure of rainwater runoff on the urban drainage network.