Putting a price tag on the flood-reducing value of wetlands

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With every big coastal storm, attention turns to the role of wetlands in reducing their destructiveness. Quantifying that service, however, is a difficult thing to do. Now a team of ecologists, engineers and risk modelers have provided two such price tags: $625 million in damage prevented by wetlands during Hurricane Sandy, and — in a New Jersey county broadly emblematic of the Atlantic coast — a 16 percent reduction in flood losses every single year.

Arriving in the aftermath of hurricanes Irma and Harvey, the figures, published in the journal Scientific Reports, underscore just how under-appreciated wetlands remain despite scientific recognition of their ability to absorb water and blunt storms. “We would like to see the scale of the benefits of these natural defenses reflected in the investments we make in conserving them,” says Siddharth Narayan, a coastal engineer at the University of California Santa Cruz and the study’s lead author.

Narayan’s team first analyzed flood heights along Hurricane Sandy’s coastal path in 2012, comparing their extent in areas where wetlands remain and areas where they’ve been lost to development. Cross-referencing those patterns with high-resolution data on property insurance claims led to an estimate of $625 million in wetlands-reduced property damage. That’s about one percent of Sandy’s toll, though the number varied widely by location. In Maryland, Delaware, New Jersey and Virginia, the states with the greatest wetland cover, property losses were reduced by between 20 and 30 percent.

The researchers then looked at annual flood patterns — not just epic, historical events like Sandy, but regular stormy weather — in New Jersey’s Barnegat Bay. There they found that properties behind salt marshes experience 16 percent less flood damage than properties unbuffered by marshes. Narayan is careful about extrapolating these findings to the entire Atlantic coast — every location is unique, wetland dynamics are complicated — but the bottom line is clear: wetlands are valuable, and potentially very valuable, during storms.

Unfortunately some 25 percent of Atlantic coast wetlands have already been lost to development, and the rate of loss has accelerated during the last two decades. It’s a doubly destructive trend. “We are developing in an area prone to flooding,” says Narayan, “and we are building over these natural defenses.” He hopes the findings will inspire new wetlands conservation and restoration projects. Only three percent of coastal infrastructure spending now goes to natural features, notes Narayan, which is “well below the sort of percentages we show for the benefits of these wetlands.”

Narayan also notes the contribution of insurance experts, and not just the usual wetlands-loving conservationists, to the research. “This is the first study to use the insurance industry’s own models to put dollar values on wetland benefits,” he says. “Hopefully we are showing that the issue matters and it is not just conservationists who think so.”

Source: Narayan et al. “The Value of Coastal Wetlands for Flood Damage Reduction in the Northeastern USA.” Scientific Reports, 2017.

Image: Alachua County / Flickr

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