Climate change influences coastal protection value of global wetlands.

Mangroves and salt marshes are effective buffers against storm waves, which are increasingly recognized as a Nature-based coastal protection measure. However, climate-driven alterations in nearshore extreme hydrodynamics (i.e., extreme wave climate and surge levels), compounded by human-induced constraints such as coastal development, may compromise these protective functions. The potential variations and impacts at a global scale remain uncertain. Here, we use global reanalysis data of wave, storm surge, and wetland distribution to quantify changes in wave attenuation by mangroves and salt marshes from 1979 to 2019. Large variations (±20%) in both wave attenuation and remaining wave height are found, mainly due to changes in incident wave height and surge levels. Furthermore, 7.6% of global coastal wetlands experienced increased remaining wave height and reduced wave attenuation capacity, indicating a seriously weakened protective effect. This proportion is projected to increase to 18.1% (95% CI: 17.9%-18.3%) globally by 2034. However, a 20% increase in wetland width (e.g., from 100 m to 120 m) can offset approximately two-thirds of this projected increase, highlighting the importance of wetland restoration. This global analysis provides an overview of contemporary viability in Nature-based coastal protection and prioritized restoration sites to adapt climate-driven hydrodynamic change.