Low-Impact Development Practices to Mitigate Climate Change Effects on Urban Stormwater Runoff: Case Study of New York City

Urban stormwater runoff management systems are usually designed to meet performance standards based on historical climate data, which are assumed to be stationary. Based on the evidence from climate change impact studies, in the near future, stormwater management systems, within the built environment, may need to meet performance expectations under climatic conditions different from historical climate. Considering the impacts of climate change on rainfall intensities and stormwater runoff peak flow and volumes, and in turn the effectiveness of mitigation, practices for urban stormwater management are desirable. This paper presents the results of a climate change impact study on urban stormwater runoff in the Bronx River watershed, New York City. Considering the impacts of climate change on watershed runoff, the potential for low-impact development (LID) controls to mitigate the impacts was investigated. Stormwater runoff and LID controls were modeled using the U.S. EPA Storm Water Management Model version 5 (EPA SWMM5). The simulations were driven by historical precipitation modified to represent future projections using a change factor methodology based on precipitation from the Coupled Model Intercomparison Project Phase 5 (CMIP5). Using the change factor method, historical precipitation was perturbed to obtain future data, based on three climate scenarios projecting maximum, mean, and minimum values for rainfall. Results of frequency analysis performed on the simulated peak flow rates, with different recurrence intervals, showed a noticeable increase in the frequency of occurrence of extreme storm events and their peak values, under future extreme climate conditions. An LID control scenario consisting of rainwater harvesting, porous pavement, and bioretention was designed and evaluated using the SWMM model. The results showed that, while average increase in historical annual runoff volume under climate change impacts was approximately 48%, the LID controls could provide an average reduction of 41% in annual runoff volume. Application of the LID controls also reduced peak flow rates by an average of 8 to 13%. LID implementation decreased watershed runoff corresponding to 2-year and 50-year return periods, by 28 and 14%, respectively. In conclusion, retrofits with LID controls may provide not only their inherent benefits (e.g., runoff volume and water quality), but also additional climate impact mitigation benefits for stormwater runoff. (C) 2014 American Society of Civil Engineers.