With continued urbanization pressure, regulators and developers alike are increasingly looking to new forms of green infrastructure and low-impact development technologies as a means of appropriately integrating built infrastructure into the landscape. This paper describes the results of a series of experiments designed to simulate the hydrologic performance of green roofs under variable precipitation conditions. The experiments were designed in order to test performance under both steady, low-intensity rainfall, as well as under short duration, high-intensity rainfall conditions. A control membrane roof and prototype green roofs of 2.5-, 6.3-, 10.1-cm depths were subjected to simulated precipitation in a laboratory setting. The green roofs delayed, prolonged, and reduced the peak rates of green roof discharge to 22–70% that of a standard roof surface, with greater percent reductions associated with deeper roofs. Negligible discharge was observed from all of the prototypes during the first 10 min of simul...

The traditional approaches to resolving urban stormwater problems include costly expansion of collections systems and/or creation of in-line storage and treatment capacity. An emerging ‘green’ infrastructure (GI) approach would instead reduce runoff sources. An agent-based model is used to explore the spatiotemporal emergence of rain gardens and green roofs in Point Breeze, a 175 ha neighbourhood in South Philadelphia, PA, under two different scenarios. In the first, household GI adoption rules consider only economic self-interest and the physical compatibility of each GI technology with lot characteristics. In the second scenario, the adoption rules are enhanced based on insights into the possible behaviour of property owners, as intuited by the designers/authors over a two-year period using a variety of empirical methods. In Scenario 2, relevant knowledge and perceptions are transferred to household decision-makers through social networks, and exposure to GI is assumed to diffuse GI innovation. The two scenarios differ in the temporal rate of GI adoption in the neighbourhood at large (greater in Scenario 1), as well as in the spatial influence of early adopters in Scenario 2, underscoring the importance of stakeholder decisions in the ultimate the effectiveness of watershed-scale GI programs.

Drainage from the 27,316-m² Jacob K. Javits Convention Center (JJCC) green roof was investigated in the field to quantify the system’s long-term rainfall-runoff response. The JJCC hosts one of the largest extensive green roofs in the United States. Utilizing four years of rooftop monitoring data collected using a weather station, custom designed and built drainage systems, three Parshall flumes equipped with pressure transducers, and weighing lysimeters, this study quantified the 25.4-mm-deep green roof’s ability to decrease the volume and peak rate of runoff. With parameters derived from the site, the Environmental Protection Agency Stormwater Management Model (EPA-SWMM) predicted event total runoff volume and event peak runoff rates to within +10% to −20% and +25% to −15% of the observations, respectively. The analysis further indicated that approximately 55% of the cumulative precipitation that fell on the JJCC extensive green roof during the monitoring period (warm weather months, June 2014–November 2017) was captured and retained. The average percent retained on an event-basis was 77%, and average event runoff coefficient was 0.7, implying a substantial reduction in the volume and rate of runoff generated from the roof compared to the pre-green roof condition, when most, if not all, of the precipitated water would have immediately resulted in runoff. Our research suggests that, on average, 96% of rainfall events 6.35 mm or less were retained within the green roof, whereas 27% of the total event volume was retained for events greater than 12.7 mm in depth. A sensitivity analysis suggests if the substrate depth were increased, better stormwater capture performance would be achieved, but only up 127 mm, whereas increased precipitation coupled with warmer temperatures as a result of climate change could decrease the performance by up to 5%, regardless of substrate depth. An equivalency analysis suggested that even shallow green roofs can significantly reduce the required stormwater detention volume that New York City requires on new development. This particular green roof appears to be more than 18 times as cost-effective as a subsurface cistern would be for managing an equivalent volume of stormwater in Midtown Manhattan.

This chapter of the New York City Panel on Climate Change 4 (NPCC4) report provides a comprehensive description of the different types of flood hazards (pluvial, fluvial, coastal, groundwater, and compound) facing New York City and provides climatological context that can be utilized, along with climate change projections, to support flood risk management (FRM). Previous NPCC reports documented coastal flood hazards and presented trends in historical and future precipitation and sea level but did not comprehensively assess all the city's flood hazards. Previous NPCC reports also discussed the implications of floods on infrastructure and the city's residents but did not review the impacts of flooding on the city's natural and nature‐based systems (NNBSs). This—the NPCC's first report focused on all drivers of flooding—describes and profiles historical examples of each type of flood and summarizes previous and ongoing research regarding exposure, vulnerability, and risk management, including with NNBS and nonstructural measures.