Performance of Green Roofs for Rainwater Control
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Performance of Green Roofs for Rainwater Control A. Raimondi 1
& G. Becciu
1
Received: 10 January 2020 / Accepted: 2 November 2020/ # The Author(s) 2020
Abstract
Green roofs can be an effective tool for sustainable urban drainage, since they reduce and retain runoff by delaying its peak. Most studies analysing the retention capacity of green roofs are usually referred to a specific place and roof condition and do not consider the possibility that the roof could be partially pre-filled from previous rainfalls at the beginning of the given event. The aim of this paper is to develop an analytical probabilistic approach to evaluate green roof performance for stormwater control in terms of runoff that could be applied for different sites and climate conditions. To this end, the possibility that the green roof retention capacity could not be completely available owing to pre-filling from previous rainfall events has been considered and equations for an optimum green roof design, relating the runoff average return interval to the water retention capacity, have been proposed. The influence of parameters affecting the runoff process has been examined in depth and a case study to test the goodness of fit of the resulting equations has been developed. Keywords Green roofs . Stormwater control . Probability . Runoff . Retentioncapacity . Pre-filling
1 Introduction The urban population of the world has grown rapidly from 751 million in 1950 to 4.2 billion in 2018. Today, 55% of the world’s population lives in urban areas, a proportion that is expected to increase to 68% by 2050 (United Nations 2018). The cover of natural surfaces causes many problems as higher temperatures, poorer air quality, increased noise levels, loss of biodiversity and greater runoffs. In particular, the reduction of infiltration into the groundwater system increases the possibility of floods and of surface waters contamination. In this context, the implementation of strategies for a sustainable urban drainage to restore the natural hydrological cycle and to minimize the environmental impact is urgent (Lee 2019; Lee et al. 2019; Li et al. 2017; Wang et al. 2019). Among these, green roofs that do not require additional space beyond
* A. Raimondi [email protected]
1
D.I.C.A., Politecnico di Milano, Milano, Italy
Raimondi A., Becciu G.
a building’s footprint could be an effective tool in densely built urban areas where rooftops constitute from 30 to 50% of impervious surfaces (Carter and Rasmussen 2007). The installation of green roofs involves numerous environmental and economic benefits, as stormwater management, energy conservation, reduction of heat islands, improvement of water quality, protection of biodiversity. Focusing on stormwater management, green roofs allow: the local disposal of runoffs; the reduction of runoff volumes, through evapotranspiration from vegetation and exposed surfaces; the delay of runoff, triggered by soil saturation; the reduction and delay of runoff peak rates, for the infiltration of rainwaters into the so
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