The role of coastal wetlands in mitigating hurricane flooding in a shallow subtropical estuary

Densely populated coastlines around the world are exposed to hazards such as storm surges from tropical cyclones. Coastal wetlands have the potential to reduce flooding during tropical cyclones by attenuating storm surge and wave energy. While previous research has demonstrated attenuation over tens of kilometers, the benefits over narrow coastal fringes remain largely unquantified. In this study, we used a 2-D high resolution model to quantify the value of coastal wetlands for flood mitigation and assess their potential role during extreme weather events. To provide context, we evaluated attenuation in Charlotte Harbor, Florida, during Hurricane Ian (2022), which made landfall as a Category 4 hurricane, costing over 150 human lives and over USD$112 billion in damages. The model, developed in Delft3D Flexible Mesh and coupled with the SWAN wave model, features an unstructured grid and an explicit representation of frictional forces caused by vegetation structure (canopy height, diameter, and density). We compared inundation depth and water velocity across four cross-shore transects under vegetated and non-vegetated scenarios and assessed structural damage costs. Results show storm surge water levels were reduced 6–17% across vegetated transects, and that wetlands attenuated storm surge an average of 36% more than unvegetated shorelines. Wetlands were also responsible for a 0.9 km2 reduction in urban inundation and estimated USD$23 million decrease in structural damage costs. By presenting a real storm scenario, this study has broad implications, as it addresses the urgent need to demonstrate the flood protection value of wetlands as coastal hazards intensify globally.