Limits of Blue and Green Infrastructures to Adapt Actual Urban Drainage Systems to the Impact of Climate Change

Abstract

Urbanization over the last few decades has resulted in a rise of impervious surfaces in municipalities worldwide. This rise has led to an increase in stormwater runoff and a decrease in the capacity of existing urban drainage systems. Additionally, the projected increase in frequency and intensity of extreme rainfall events due to climate change further exacerbates the risk of urban flooding. In response to this challenge, many municipalities have begun implementing blue and green infrastructures (BGI) to mimic the natural hydrologic cycle and manage stormwater at its source. Although the benefits of BGI, such as bioretention cells, permeable pavement, blue roofs, and green roofs, have been demonstrated, their full potential remains uncertain. This raises the question of whether BGI, when utilized to the maximum potential, can effectively adapt our existing drainage infrastructures to the projected increases in extreme rainfall in a warmer climate. To address this question, a case study was conducted in the Pointes-aux-Trembles District, a 20-km2 urban catchment in Montreal. A calibrated stormwater management model [personnel computer storm water management model (PCSWMM)] was used to simulate various scenarios of BGI implementation, both individually and in combination without considering economic constraints. An extreme rainfall event was simulated under a warming climate to compare urban flooding between the existing urban drainage system and the different BGI scenarios. The results demonstrated the significant potential of BGI in adapting our existing drainage systems to climate change. In the simulated scenario of climate change impact, which resulted in a 136% increase in flood volume, the individual implementation scenarios offset between 20% and 118% of this increase. Furthermore, the combination scenarios achieved offsets of 162% and 167%, resulting in a better performance of the urban drainage systems (UDS) under climate change conditions with BGI practices than in historical conditions without any BGI practice. These findings strongly suggest that BGI practices should be considered as a crucial part of the adaptation solution. The growing trend of urbanization leads to an increase in impervious surfaces across municipalities worldwide, which in turn exacerbates stormwater runoff managed by urban drainage systems. Compounded by climate change, this trend heightens flood risks. To counteract this, many municipalities are adopting BGI, which mimic the natural hydrological cycle, to manage stormwater at its source. Although BIGs are recognized for their benefits, their full potential is yet to be fully understood. This case study utilized a stormwater management model in a district of Montreal to simulate various BGI implementation scenarios without considering economic constraints. The results indicated significant potential for BGIs to adapt UDS to the impact of climate change. When implemented, individual types of BGIs showed potential to offset between 20% to 118% of the increase in flood volume. Scenarios that combined different BGIs showed even more promise, reducing flooding by 162% to 167%. These outcomes not only mitigate the impact of climate change but also enhance the current capacity of UDS. In conclusion, BGIs represent a promising solution to the dual challenges of urbanization and climate change by effectively managing stormwater and enhancing the resilience of municipalities to flooding.