Species-specific wave attenuation and cost-effectiveness of mangroves for hybrid coastal defense.

Rising sea levels and intensifying storm surges are amplifying flooding risks in tropical and subtropical coastal regions under climate change. Conventional concrete structures provide reliable flood protection but they are increasingly criticized for their low ecological value and high maintenance costs. As an alternative, nature-based hybrid coastal protection systems, which combine engineering dikes with mangrove foreshores, are gaining recognition for providing both flood mitigation and ecological benefits. However, the wave attenuation performance and cost-effectiveness associated with different mangrove species, especially under extreme storm conditions, remain poorly understood. In this study, we employed the SWAN-VEG model to evaluate the wave attenuation capacity and cost-effectiveness of three representative mangrove species under a range of sea-level rise and storm surge scenarios. Results revealed that Rhizophora stylosa exhibited the highest wave attenuation, while Avicennia marina was the least effective. Generally, vegetation-induced wave dissipation exhibits various response patterns with rising sea levels and storm surges. Cost-effectiveness analysis showed that the hybrid system dominated by R. stylosa achieved the most economic and efficient protection against dike overtopping within a vegetation width of 50-100 m. These findings advance understanding of species-specific performance in hybrid coastal defenses and offer guidance for adaptive shoreline planning under climate change.