Vegetative nature-based solutions for coastal flood risk management: Benefits, challenges, and uncertainties

Coastal regions, home to more than one-third of the world's population, face increasing flood risks due to sea-level rise and intensifying storms under climate change. Traditional ‘grey’ solutions, such as seawalls and groynes, while effective at a local scale and over the short-term, are costly, disrupt natural ecosystems, and have adverse ripple effects for downdrift coastal areas. Vegetative forms of Nature-Based Coastal Solutions (NBCS), which include the use of mangroves, saltmarshes, and seagrasses, offer a sustainable alternative, with wider environmental benefits apart from just coastal flood risk reduction. In this review, we examine the effectiveness of vegetative NBCS in mitigating coastal flood risk and consider the limitations, challenges and uncertainties around their implementation. We find that mangroves, saltmarshes, and seagrasses significantly reduce wave energy, attenuate storm surges, and stabilise sediments, with evidence showing up to a 72% reduction in wave energy by saltmarshes and a 66% reduction in wave height by mangroves. Also, we find that these ecosystems have the potential to contribute to long-term coastal resilience through carbon sequestration, biodiversity enhancement, and shoreline stabilisation. However, the effectiveness of these solutions can vary based on vegetation density, species type, and environmental conditions, pointing towards the need for targeted management efforts. Additionally, there are several ecological, environmental, socioeconomic, policy and geomorphology challenges associated with implementing vegetative NBCS. We discuss these as well as identify critical knowledge gaps on NBCS understandings for coastal flood risk management and outline new research pathways to address these gaps. Our review, therefore, has important implications for refining coastal flood risk management (both understandings and approach), communication strategies, and policies towards enabling more robust decision-making for sustainable coastal flood risk management.