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To Soften a Hurricane's Blow, Don't Drain the Swamp

By Robinson Meyer, The Atlantic

05 September 17

Wetlands directly prevented half a billion dollars in damages during Hurricane Sandy, a new study has found.

f a hurricane-addled storm surge is barreling toward your coastline, there aren’t many ways to stop it. There are no ocean-sized sump pumps. Giant, Squarepants-style coastal sponges don’t exist either.

Except they kind of do. Wetlands and marshes—the water-permeated thickets of grass and muck that sit on the edge of much of the Atlantic coast—can slow the extra sea water and absorb the surge’s excess energy. They are, in their way, continental sponges. And a new study finds that, when a flood comes, they can prevent hundreds of millions in damages.

Wetlands prevented more than half a billion of dollars in direct damages across the mid-Atlantic United States during Hurricane Sandy, a study published this week in Scientific Reports has found. The research is the first to use the insurance industry’s own simulations to calculate the economic benefits of conserving wetlands.

It attests to the quantifiable value of conservation. “A lot of these studies about how marshes work are done by ecologists like myself. It was really important we were able to work with the industry and say, ‘Your data and your models already account for marshes. It shows up in your premiums already,’” said Michael Beck, an author of the study and the lead marine scientist at the Nature Conservancy.

Beck and his colleagues arrived at their estimates by running industry-standard insurance models for the Eastern Seaboard twice. First, they asked it to compute damages from a storm surge that was directly observed during Hurricane Sandy. Second, they used the same storm-surge data, but told the insurance model to pretend all the available coastal marshes were open water instead.

They found that wetlands were economically beneficial in two situations: if there were a lot of them or if they were near something expensive.

They calculate that in the four states with the most conserved marshland—Maryland, Delaware, New Jersey, and Virginia—the economic damage of Hurricane Sandy was between 20 and 30 percent smaller than it could have been. In New Jersey, where 10 percent of the land area is wetland, conserved marsh staved off $430 million in damages.

These benefits extended miles from the site of the wetlands themselves. Hamilton Township in Atlantic County, New Jersey, for instance, would have seen its damages more than double were it not for coastal wetlands 15 miles away, at the mouth of the Great Egg Harbor River.

But there were also benefits to preserving wetland near dense and expensive real estate. Marshes only cover 2 percent of New York state. Yet through their proximity to New York City, they managed to stave off $140 million in damages.

“Those wetlands were remarkably effective in Hurricane Sandy even though they’re pretty urban.” said Siddharth Narayan, an author of the paper and an ocean scientist at the University of California, Santa Cruz. “I was actually surprised at the value of those wetlands.”

Of course, with plains of floodwater still stretched across Houston, the study can seem more than academic. Beck told me its timing was an accident, though the fifth anniversary of Hurricane Sandy does fall next month.

“You wouldn’t normally choose to [publish] this in a response period, when so many people are still at risk,” Beck told me, alluding to Hurricane Harvey. “But we do hope that this is the kind of thing people think about during recovery and rebuilding phases.”

And it does raise the question: Could more wetlands have staved off some of Harvey’s devastation? Over the past few decades, many square miles of marshes have been paved over in the Houston area. Between 1992 and 2010, Harris County lost almost 30 percent of its freshwater marshland. And the Texas Coastal Watershed Program estimates that the greater Houston area saw more than 5 percent of its wetlands vanish during the same period.

Yet Harvey and Sandy are different types of storms—and their floods had different root causes. Sandy, like Hurricane Katrina, wreaked so much havoc because of its storm surge. Harvey, on the other hand, more closely resembles Hurricane Irene, the August 2011 storm whose floods were caused by high levels of inland rainfall.

Wetlands can help prevent freshwater, rain-powered floods—like those seen during Harvey and Irene—by soaking up the excess water. But Beck and Narayan’s study only examined their benefit in stymieing storm surge. They hesitated to say if its findings would extend as strongly to Harvey-style freshwater flooding.

The research was conducted by university scientists, risk-modeling experts, and ecologists employed by the Nature Conservancy, a nonprofit that preserves millions of acres of land and water across the United States. It was funded by a charity managed by Lloyd’s of London, a major insurance company.

Ecologically speaking, scientists already consider marshes to be among the best refuges for biodiversity in the world. So wetlands offer plenty of nonmonetary, planetary insurance already—but that value is, of course, harder to quantify.