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.