Nature-based coastal defence solutions have increasingly been recognized as more sustainable alternatives to conventional engineering approaches against climate change. In deltas undergoing fast urbanization, applying nature-based solutions can lead to space competition with other land uses, e.g. land-reclamations. For optimized management, the question of how much space is required by nature-based solutions is important. However, our current knowledge is insufficient in ecosystem size-dependent defence-value and resilience. Additionally, we are lacking insights into ecosystem creation for coastal defence, as previous restoration efforts have suffered low success rate. The current proposal aims to develop process-based understanding and predictive models of ecosystem size requirements and how to create ecosystems for coastal defence, using the world’s largest urban area, Pearl River Delta, China, as a model system. Delta-scale mangrove area monitoring and hydrodynamic modelling will be conducted to study wetland area changes and optimization of ecosystem spaces for defence, under contrasting scenarios of climate change and land-reclamations. This large-scaled study will also provide underpinning boundary conditions for local-scaled experiments and modelling. A set of experiments using novel instruments will be conducted to improve our insights on the processes influencing mangrove defence-value and lateral dynamics. Innovative measures of using dredging materials and oyster reefs to facilitate mangrove establishment will also be tested experimentally. Local-scaled models will incorporate the obtained experimental knowledge to predict mangrove biogeomorphic dynamics and provide guidelines for management. The developed models and knowledge will be directly applied in the design of a pilot eco-dike project in collaboration with our partners.