Integrating green and grey infrastructure systems in dense urban regions: a synthesis of critical barriers and effective implementation guidelines

Abstract Green infrastructure (GI) and ecosystem-based solutions (ES) have gained significant attention as effective climate adaptation strategies in dense urban regions. However, integrating these systems into existing infrastructure encounters profound barriers due to current land use policies and stakeholder priorities. Consequently, integrated systems such as green and grey infrastructure (GGI) require effective planning and implementation frameworks to ensure project success. The current systematic review explores the existing divide between conventional (grey infrastructure) systems and green infrastructure systems. The review employed interaction maps and fishbone diagram analysis to synthesise critical barriers and effective implementation guidelines for GGI projects. The analysis covers how GGI outweighs standalone components such as GI and grey infrastructure in several climate resilience scenarios such as flood damage control and meeting sustainability goals. Thus, the review provides compelling arguments to cement the GGI integration debates. Multiple stakeholder objective misalignment and path dependency on grey infrastructure were perceived as critical barriers at the planning stage. The design stage is hindered by the inadequacy of performance data, while large space requirements in dense urban settings present some implementation challenges. The review recommends the need to intensify concerted efforts in holistic GGI economic evaluation considering the social dimension and improving community participation through mutual collaboration. Graphical Abstract