What Value do Natural Coastlines have in Reducing Hurricane Storm Surge Risk?

In a world where coastlines are becoming increasingly developed, the economic risk posed by hurricane storm surges to coastal communities has never been greater. Given the financial and ecological costs of armouring the coastline with artificial flood defences, the past few years have seen growing interest in the effectiveness of natural defences in reducing the coastal flooding risk from storms and hurricanes.

In this study we aim to quantify the economic benefit of natural defences in reducing property damage from hurricane storm surge flooding, by employing a catastrophe modelling framework commonly used in the insurance industry. Focusing on the North-Eastern USA, we first estimate the damage reduction benefits of wetlands during Superstorm Sandy to have been in the region of $625 Million, and show that these benefits are distributed heterogeneously along the event footprint. Wetlands were found to have reduced flood damage in 80% of ZIP codes flooded by Sandy, and States with higher wetland coverage were found to have seen the greatest reduction in damages from wetlands. The benefits of wetland conservation are seen to accumulate upstream, with some communities with few wetlands within their boundaries benefitting from the cumulative surge reduction from several kilometres of downstream wetlands.

We also estimate the impact of salt marshes on Average Annual Losses from storm surge flooding to properties in Ocean County, New Jersey, and find that properties behind marshes have losses up to 16% lower than in watersheds where marshes have been lost. The damage reduction benefits are found to be much greater for properties at lower elevations.

Together these studies aim to financially quantify some of the risk reduction services provided by natural defences against coastal flooding from hurricanes in the USA, and show that these services can be included in a catastrophe modelling framework.