Abstract
Abstract Rooftops cover a large percentage of land area in urban areas, which can potentially be used for stormwater purposes. Seeking adaptation strategies, there is an increasing interest in utilising green roofs for stormwater management. However, the impact of extreme rainfall on the hydrological performance of green roofs and their design implications remain challenging to quantify. In this study, a method was developed to assess the detention performance of a detention-based green roof (underlaid with 100 mm of expanded clay) for current and future climate conditions under extreme precipitation using an artificial rainfall generator. The green roof runoff was found to be more sensitive to the initial water content than the hyetograph shape. The green roof outperformed the black roof for performance indicators (time of concentration, centroid delay, T50 or peak attenuation). While the time of concentration for the reference black roof was within 5 minutes independently of rainfall intensity, for the green roof was extrapolated between 30 and 90 minutes with intensity from 0.8 to 2.5 mm/min. Adding a layer of expanded clay under the green roof substrate provided a significant improvement to the detention performance under extreme precipitation in current and future climate conditions.
Highlights
Climate change is increasing the exposure and vulnerability of urban environments to local flooding
Data from concatenation were monitored under different conditions, inner porosity was saturated, which could have led to underestimating time of concentration (TC)
A method to test extreme precipitation on a full-scale detention-based green roof consisting of sedum mats underlaid with expanded clay was developed using an artificial rainfall simulator
Summary
Climate change is increasing the exposure and vulnerability of urban environments to local flooding (among others: Few 2003; Miller & Hutchins 2017; Hettiarachchi et al 2018). Norway has adopted a three-step approach to stormwater management, where step 1 aims to infiltrate all small events onsite (a well-established and effective solution to reduce peak runoff from impervious surfaces), step 2 aims to safely detain all medium-size events, while step 3 aims to ensure safe floodways for all extreme events (Lindholm et al 2008). Little research has been conducted on the performance of green and grey roofs during extreme events. Extreme events, by their nature, occur neither regularly nor frequently, and they are difficult to capture. This is why several scenarios depending on impact of human activities on climate have been developed to evaluate and predict this change (Hanssen-Bauer et al 2017)
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