Analysis of the Effects of Climate Change on Urban Storm Water Runoff Using Statistically Downscaled Precipitation Data and a Change Factor Approach

In urban areas, there is concern that storm water runoff and flooding may be intensified because of the effect of climate change on precipitation amounts, intensities, and frequencies. Studies are needed to help storm water managers to plan and design effective adaptation and mitigation measures. This paper presents a study of the effects of climate change on urban storm water runoff in the Bronx River watershed in New York City. To show the effects of climate change on future precipitation, projections by 134 general circulation models (GCMs) from the fifth phase of the coupled model intercomparison project (CMIP5) are used. A new change factor method is proposed to select minimum, maximum, and mean daily precipitation scenarios for a future time period of 2030-2059. Because of the importance of short duration for extreme storm events, the daily precipitation is disaggregated to hourly increments. The U.S. Environmental Protection Agency storm water management model (SWMM) is used to model the hydrologic response and is driven by 30years of the produced hourly precipitation corresponding to the three climate change scenarios. The simulated runoff results showed increase in volume and peak discharge. Considering the climate scenarios for future planning purposes, frequency analysis is performed on the projected runoff which shows a considerable increase in the frequency of occurrence of extreme storm events and their peak values. To further analyze the runoff response at the subwatershed level, a storm water climate sensitivity factor (SCSF) is proposed. This sensitivity factor indicates the potential of subwatersheds' runoff sensitivity to climate change based on the subwatersheds' characteristics such as area, width, slope, and imperviousness. Results of analysis of SCSF show that storm water runoff in a changing climate is more sensitive to subwatershed slope, rather than the other subwatershed characteristics. Subwatersheds with SCSF more than 0.1 show a runoff volume increase of 40% or more, under the effects of climate change. Based on the potential increase in peak discharges, retrofit measures are recommended to provide additional storm water management capacity.