[Effects of a Green Roof on Stormwater Regulation and Cost-benefit Analysis]

Increasingly frequent urban waterlogging disasters, which are mainly caused by the increase in impervious surfaces due to rapid urbanization, have attracted public attention. Green roofs are conducive to increasing the urban pervious surface area to control sources of runoff, which has great significance for the ecological environment. This study uses the green roof of the administrative building of Jinling Primary School in Nanjing as the study area. 76 rainfall-runoff events collected over 17 months (2016-06-2017-10) were used to calculate the comprehensive runoff control ability and factors influencing the green roof in the context of the site scale. Based on life cycle assessment theory, the benefits of stormwater regulation over its 30-year life cycle were quantitatively evaluated. The results show that:① The average retention of the green roof was 62.7%, which could have a significant impact on runoff and peak flow, reducing the runoff time and delaying the flood peak. ② The green roof has a strong ability to retain runoff during small and medium rainfall; however, this ability becomes low when the retention capacity is saturated or not fully recovered, even in small rainfall-runoff events. ③ The main factors affecting the retention ability of the green roof are the total rainfall, rainfall intensity, and water content of the growth substrate soil. ④ The green roof has great economic benefits, with a construction cost of about 12.51 yuan·m^-3 and a return on investment of 0.41. The results of this study can provide an important scientific basis and decision-making reference for the planning and construction of green roofs and the promotion of related policies.