Multi-objective optimisation of integrated grey-green infrastructure in response to climate change from a life cycle perspective

Integrated grey-green infrastructure is widely recognized as a promising approach to addressing urban flooding resulting from climate change and many scholars have conducted optimisation studies to reduce its economic costs and enhance its functional performance. However, as the concept of sustainable development garners increasing attention and the pace of global warming accelerates, it is clear that these traditional optimisation objectives of saving economic costs and improving hydrological performance cannot meet the requirements of the Sustainable Development Goals. Therefore, a representative site in Guangzhou, China, was used to carry out a multi-objective optimisation to achieve the trade-off between economic and environmental costs. Furthermore, a multi-criterion decision-making method was also employed to find the optimal layout based on the economic cost, environmental cost, and corresponding hydrological performance under climate change in the life-cycle of each layout in the optimised solution set. The results indicated that: (1) Decentralised layouts require lower economic and environmental costs, and as decentralisation increases, the similarity of cost levels among optimised layouts increases. (2) Integrating a higher percentage of green infrastructure improves hydrological performance and reduces carbon emission costs by up to 80%. (3) Optimised IGGI systems outperform single grey infrastructure systems in economic, environmental, and hydrological aspects, achieving maximum improvements of 75%. (4) The use of permeable pavement may be cost-effective and effective in managing runoff, but it may exacerbate carbon emissions. This framework offers a comprehensive, scientific, and sustainable methodology for urban regions to adaptively manage stormwater in light of climate change. It lays the groundwork for future investigations into optimising such frameworks for diverse urban settings, exploring scalability, and integrating technological advancements. This paves the way for a dynamic evolution of stormwater management strategies, adaptable to changing environmental and urban landscapes.