Evaluation of the Impact of Climate Change on Runoff in Urban Watersheds

Existing drainage systems, which were already susceptible to degradation, are now facing even greater challenges due to the impacts of climate change. This could compromise their overall ef-fectiveness. This project aims to develop an innovative methodology for assessing the impacts of climate change on urban runoff. The proposed methodology relies on modeling synthetic urban watersheds using the United States Environmental Protection Agency's (US EPA) Storm Water Management Model (SWMM) software, and the use of rainfall data from different meteorological stations with a variety of durations and frequencies.

Results showed that using a simple increase of 18% in rainfall to estimate the impacts of climate change led to larger relative increases in peak flow, with median variation of 24.7%, and median variations in runoff volumes of 18.0% and a result dispersion depending on the station, frequency, and duration of rainfall. This suggests that the impacts of climate change on extreme rainfall events cannot simply be translated into similar increases for peak flow and runoff volumes.

Through a sensitivity analysis (ANOVA), it was found that among all the criteria tested, impermea-bility, area, and slope have a greater influence on peak flow changes under a future climate. Addi-tionally, impermeability emerged as the most critical parameter affecting runoff volume across all stations, although certain stations exhibited variations where soil type played a more prominent role. This study reiterates the importance of reducing soil impermeability in the urban water cycle, notably through the use of blue-green infrastructures, to mitigate the impact of climate change on existing urban drainage systems.

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