Scale dynamics of extensive green roofs: Quantifying the effect of drainage area and rainfall characteristics on observed and modeled green roof hydrologic performance

Green roofs offer many benefits for dense urban environments, one of which is their potential to supplement existing stormwater management infrastructure. The ability of green roof systems to act as a decentralized rainwater retention and detention network has been the topic of many recent studies. While these studies have provided important insight into the hydrologic performance of green roofs, none to date, to the knowledge of the authors, have specifically examined the effect of green roof drainage area on system performance in an urban climate. This research aims to understand how rainfall characteristics and green roof scale impact the peak and cumulative volume of green roof runoff during individual storm events. The performance of three extensive green roofs in New York City, each having the same engineered components and age but different drainage areas, is analyzed. It is found that green roof drainage area has the greatest impact on peak runoff reduction peak runoff reduction increases with increasing drainage area whereas rainfall retention and the time to peak runoff are not greatly influenced by drainage area. Data collected from the three green roofs are used to examine the applicability of a one-dimensional infiltration model, HYDRUS-1D, in predicting hydrologic behavior across the different green roof spatial scales. It is found that model performance improves as the green roof drainage area and rainfall volume increases. However, in general, HYDRUS-1D is only partially able to capture the hydrologic behavior of extensive green roofs across the different rooftop scales examined during this study. (C) 2014 Elsevier B.V. All rights reserved.