Incorporating natural habitats into coastal risk assessment frameworks

The coastal risk assessment (CRA) has important implications for policy development, resilience enhancement, and risk reduction to reduce the magnitude and likelihood of future losses to coastal hazards. However, few if any existing in-practice CRA approaches account for the effects of coastal natural habitats (CNHs), which shield communities from natural hazards and support resilience enhancement in coastal regions. Here, we use a coupled human-nature system-based CRA framework to provide evidence on the influence of CNHs on coastal storm-risk levels and spatial distributions. We calculate a risk index for each coastal county along the U.S. Atlantic coast and employ different spatial assessment approaches to systematically analyse the risk. This index incorporates several bio-geo-physical variables (e.g., geomorphology, natural habitats, coastal relief, and historical data on sea level trends, wind, and wave) and data on socio-ecological systems. The index is calculated under two CNH scenarios (i.e., without- and with-habitat) and is further used for mapping the at-risk population. We find that the without-habitat scenario overestimates the population in the highest risk category by 10 % and the number of counties by as much as 40 % as compared to the with-habitat scenario mostly in the Gulf region. Also, the without-habitat scenario miscalculates the spatial distribution of the risk (e.g., over/under-estimate the relative risk for Florida/New York). These findings highlight the role of CNHs to provide defensive services and the importance of incorporating CNHs into the risk assessment process. While the CNHs inclusive risk results are important for coastal risk-reduction through prioritization and smart resource allocation, the well evident influence of CNHs on risk level and its distribution is also supportive for conservationists to stress the policies relevant to the protection and restoration of coastal natural systems owing to their multiple services.