Coastal Wetlands Provide Significant Flood Damage Reduction

Recently released report on Coastal Wetlands and Flood Damage Reduction uses industry-based risk models to assess natural defenses in the Northeastern USA

Visit http://www.lloyds.com/coastalresilience to download the full report.

On the four year anniversary of Hurricane Sandy, a new study puts a dollar value on the risk reduction benefits provided by coastal wetlands in the Northeast United States. The report, Coastal Wetlands and Flood Damage Reduction, uses industry-based risk models to study the flooding and storm surge impacts of Hurricane Sandy along the US’s northeast coast.

Hurricane Sandy caused devastating flooding and become the second costliest hurricane in US history. This research finds that coastal wetlands prevented more than US$625 million in property damages during Hurricane Sandy, reducing property damages throughout the Northeast US by 10% on average. The research finds that the benefits of wetland conservation accumulate upstream: some places with few wetlands within their boundaries nevertheless benefited from the cumulative surge reduction of wetlands downstream.

The study also examined the benefits of wetlands through the year in Ocean County, New Jersey, and finds that areas behind existing salt marshes have 20% fewer property damages on average when compared to areas where salt marshes have been lost. Properties built on previously existing wetlands, and properties at low elevations, face the greatest risk from flooding, and therefore derive the greatest protection benefits from coastal wetlands.
As the likelihood and costs of hurricanes like Sandy continue to increase, coastal communities need for a more effective suite of strategies for risk reduction. Coastal wetlands and reefs provide a natural defense from flooding and storm surge, but these habitats are being degraded or lost at alarming rates. This report provides one of the few existing assessments of the economic costs and benefits of the role of coastal wetlands in reducing flood damage to properties. The report shows that coastal wetlands can reduce property damage from storms, and that these protection benefits can be readily incorporated and accounted for in the insurance industry’s risk models. This research will help inform (i) risk reduction and conservation management priorities and (ii) the development of incentives for the conservation and restoration of natural defenses.

This work is supported by the Lloyd’s Tercentenary Research Foundation, and was led by the University of California Santa Cruz, The Nature Conservancy, and the Wildlife Conservation Society, in association with Risk Management Solutions and Guy Carpenter and Company, with additional support from the Science for Nature and People Partnership.

Learn more at http://www.lloyds.com/coastalresilience

Caption for Figure 4
Predicted increases in property losses if marshes had not been present during Hurricane Sandy (click on image to enlarge).

Sandy Census tracks show the percent changes in flood damages that would have occurred during Hurricane Sandy without coastal wetlands. Dark red areas derive the greatest protection benefits from today’s coastal wetlands.

From the Executive Summary:

There are three key messages from this report

• Risk industry-based tools are used to quantify the economic benefits of coastal wetlands for property damage reduction from hurricane-induced flooding in the northeastern USA.
• It is estimated that during Hurricane Sandy, temperate coastal wetlands saved more than $625 million in flood damages and hundreds of millions of dollars in New Jersey alone. Where they remain, wetlands reduced damages by more than 10% on average.
• In Ocean County, New Jersey, salt marsh conservation can significantly reduce average annual flood losses by more than 20%.

We quantify the economic benefits of coastal wetlands in reducing property damage from storms and flooding in the northeastern United States (USA). In 2012, Hurricane Sandy hit the northeastern coast of the USA causing devastating flooding and becoming the second costliest hurricane in USA history. As the likelihood and costs of hurricanes like Sandy continue to increase, there is a need for a more effective suite of strategies for risk reduction. There is great interest in the role of coastal wetlands and reefs as natural defenses in reducing some of this risk, especially where these ecosystems are being degraded or lost. While there is substantial evidence for the physical ability of wetlands to attenuate waves, there have been fewer assessments of the economic costs and benefits of their role in reducing flood damage to properties. This has limited their consideration by public agencies and private industries.

Using risk industry based flood models, we predict the increase in damages from Hurricane Sandy that would have occurred if wetlands had been lost. We estimate that coastal wetlands saved more than US$ 625 million in avoided flood damages from Hurricane Sandy across the northeastern USA. For census tracts with wetlands, there was on average a 10% reduction in property damages across the region. The damage reduction benefits varied by state and reached as high as 29% for Maryland. We also find that the benefits of wetland conservation accumulate upstream. Some townships with few wetlands within their boundaries nevertheless benefited from the cumulative surge reduction of wetlands downstream. Wetlands can also increase flood heights and damages to some properties by blocking the flow of water and causing it to pile up, which is similar to effects observed for artificial defenses such as seawalls or levees.

To examine the benefits of wetlands beyond an individual hurricane, we estimate the effects of salt marshes on annual flood losses to properties in Ocean County, New Jersey for 2000 storm events. Areas behind existing marshes are predicted to have an average of 20% less property losses than areas where marshes have been lost. These benefits of salt marsh conservation for damage reduction are much higher for properties at lower elevations.

Together, these studies illustrate the direct and indirect flood risk reduction benefits that coastal wetlands provide by reducing flood heights and also by decreasing exposure. We show that coastal wetlands can reduce property damage from storms and that these effects can be readily incorporated into the insurance industry’s risk models. These results help inform (i) risk reduction and conservation management priorities and (ii) the development of incentives for the conservation and restoration of natural defenses.