Green Roof Performance in Sustainable Cities

In the last few decades, the use of sustainable urban drainage systems is largely spreading and encouraged, because they provide lots of benefits for sewer networks, wastewater treatment plants and the environment. In this context, green roofs can be an effective tool to both delay and attenuate stormwater runoff peaks, reducing runoff at the same time. Their proper design is a key element for stormwater management in highly urbanized cities. The aim of this paper is to propose an analytical probabilistic approach, to evaluate green roof performance in terms of runoff and vegetation’s survival without irrigation, to guide planners in choosing proper values for their design parameters. A great advantage of the method is that it can be applied to different sites and climate conditions; moreover, it involves a significant improvement of the typical analytical probabilistic approach, as a chain of consecutive rainfall events was considered, in order to take into account the possibility that storage capacity is not completely available at the beginning of each event, because of pre-filling from previous rainfalls, as typically happens with green roofs. Finally, to verify the goodness of our developed equations, we applied them to a case study.