Optimization of Blue and Green Infrastructures in a Sustainable Muti-Criteria Analysis

The increasing frequency and intensity of rainfall extreme events due to climate change pose significant challenges to urban drainage infrastructure. Traditional gray infrastructure, designed under the assumption of stationarity, is increasingly inadequate for managing stormwater runoff. Previous research demonstrated the potential of blue and green infrastructures (BGI) to enhance the climate resilience of drainage urban infrastructure. In Montreal's Pointe-aux-Trembles district, their study found that individual BGI implementations could offset between 20% and 118% of the additional flood volumes caused by climate change, while combined BGI scenarios achieving offsets of up to 167%.

Building on these findings, this study investigates the optimization BGI as sustainable and adaptive alternatives to conventional drainage systems within the same 20 km2 watershed in Montreal. Using a calibrated PCSWMM model, different BGI scenarios were tested under projected future climate conditions. The results were analyzed using the PROMETHEE II multi-criteria analysis method under the PyDecision Python library, considering economic, social, technical, and environmental factors.

This study provides a comprehensive assessment of the wide-ranging benefits and impacts of BGI strategies, including economic implications such as construction and maintenance costs, ease of implementation, job creation and potential property value increases; technical implications, such as peak outflows, flood and runoff volumes; environmental aspects, such as water quality improvements, heat island mitigation; and social factors such as public acceptance, aesthetic improvements, and community benefits.

The results are presented as PROMETHEE IIscores of the relative performance of each BGI strategy across the criteria previously described. The findings indicate valuable insights into which BGI, and combination of BGI, are the most sustainable, cost-effective, and resilient stormwater management adaptation strategies in the face of climate change. They will help municipalities make informed, data-driven decisions to enhance flood resilience, improve environmental quality, and create more livable urban spaces