Characterization of Urban Green Roof Stormwater Runoff

Green roof planning and design is considered as one of the green technologies towards the development of sustainable urban environment and building eco-friendly cities. The benefits of implementing green roof strategies are numerous, such as reducing the urban heat island effect, etc. From the perspective of stormwater control, as more and more rooftops in the urban area turn into green spaces, characteristics of stormwater runoff from the drainage area may undergo a significant change which will inevitably impact on the existing and yet-to-be-built drainage systems. However, in addition to peak flow reduction, basic understanding of the characteristics of green roof stormwater runoff is either lacking or very limited, and referenced green roof studies are very few in the literature.

In this study, based on a set of rooftop-monitored data including the antecedent soil moisture content, rainfall, runoff volume and peak flow rates, stormwater runoff from both the green roof area and the control area (the original rooftop without greening) was analyzed for its characteristics. It is well known that the antecedent soil moisture content is an important parameter associated with runoff generation, whereas runoff coefficient is a direct measure of the rainfall-runoff transformation process. These fundamental relationships are characterized in an attempt to better understand runoff generation mechanisms from green roofs. As part of this study for stormwater runoff characterization, probability distributions were fitted to sample data of the rainfall, runoff volumes and peak flow rates monitored from the green roof and control area, respectively. The statistical behavior of stormwater runoff from the two areas is evaluated and the best fit probability distribution may be determined. It is of interest to determine whether some commonly used probability distributions can be used to fit green roof stormwater data as well.