A critical review on optimization and implementation of green-grey infrastructures for sustainable urban stormwater management

Green-grey infrastructures’ implementation has progressed significantly in cities around the globe for sustainable stormwater management. This review study conducted on green-grey infrastructures’ optimization represented recent research trends, existing research status, possible study gaps, and future research directions and recommendations needed for further improvements. The findings show that the research on green-grey infrastructures has got significant attention recently (after 2012) because of accessibility to computational resources and the development of hydrological-hydraulic models and optimization algorithms. Furthermore, research on green-grey infrastructures is mostly conducted in ten countries including China, USA and Iran ranked in the first three places, respectively, delivering their advantages to other countries with the essential awareness and knowledge. Most previous studies considered particular quantitative and qualitative optimization objectives and these studies were conducted at smaller retrofitting scales, therefore, future studies need to expand their scope towards socio-ecological objectives with consideration of larger study areas or multi-stage planning, designing, and implementation. Moreover, future research is recommended to consider stakeholders’ participation in preliminary planning and designing stages for the successful implementation of sustainable stormwater management approaches. Lastly, the surrogate-based optimization approaches instead of traditional optimization methods can overcome the burden of computational time and resources in future.