If the United States lost its shield of natural coastal defenses, about twice as many Americans would be exposed to dangerous storm surges and other hurricane threats, according to new research.

Protective buffers like mangroves, wetlands and oyster beds currently buffer about 67 percent of the nation's seashores from ocean forces like wind and waves. If they disappear, more than a million additional people and billions of dollars in property value will be vulnerable to damage, says a paper published yesterday in the journal Nature Climate Change.

"Habitat loss would double the extent of coastline highly exposed to storms and sea-level rise, making an additional 1.4 million people now living within 1 km of the coast vulnerable," the paper says.

The project wades into a sensitive topic about the rapid pace of coastal development in the U.S. by providing what the authors say is the first national map to outline the risks of seashores that are depleted of their wave-breaking ecosystems.

In addition to documenting the amount of defensive ecosystems in the U.S., the researchers fed data about property values, population, income and age into a model that tested four sea-level rise scenarios. They found that between 1.7 million and 2.1 million people will live in "high hazard" areas by 2100. Of those, up to 40,000 families will be below the poverty line and between $400 billion and $500 billion in residential property will be vulnerable to damage.

Currently, about 16 percent of the U.S. coastline is considered high hazard areas, with 1.3 million people, of whom 250,000 are elderly, and $300 billion in residential property value. The authors say their estimates in all likelihood are lower than what will actually occur, because they don't account for population growth and property value increases over the 83-year period.

"By quantifying where and to what extent habitats reduce the exposure of vulnerable populations and property, our analyses are, to the best of our knowledge, the first to target where conservation and restoration of coastal habitats are most critical for protecting lives and property on a national scale," the paper says.

Fla., N.Y. have problems

Katie Arkema, an ecologist with the Natural Capital Project at Stanford University and a co-author of the paper, said the research assumes that all natural barriers would disappear to show how individual states, counties and communities would be affected if it happened.

"That's unrealistic that that would happen, I think, anytime soon around the entire shoreline of the U.S.," Arkema said. "But it is realistic that that will happen in places throughout our shoreline, especially in places that are experiencing the most pressure from coastal development."

She noted that it was surprising to see the number of people exposed to risk double under the scenario.

"I never expected for it to be that big of a difference," she said.

The East Coast and Gulf Coast would feel the largest impacts from depleted ecosystems, because they have denser populations and are more vulnerable to sea-level rise and storm surge.

Florida would see the largest increase of people exposed to hazards by 2100 under one sea-level rise scenario highlighted by the researchers. If coastal habitats were preserved, about 500,000 Floridians would face intermediate and high risk from disasters, compared with almost 900,000 people if the habitats disappeared.

New York sees one of the biggest jumps as a percentage of people facing risk under the same scenario. With habitat, a little more than 200,000 people would face high risk, compared with roughly 550,000 people without habitat.

The Natural Capital Project partners with the University of Minnesota, the World Wildlife Fund and the Nature Conservancy. The findings will be used in part by the Nature Conservancy to help direct federal funding toward ecosystem restoration and conservation projects that protect the most people and property, Arkema said.

She added that natural barriers are just one strategy in a suite of defensive efforts that also include infrastructure and requirements to build farther back from the shore.

"We're not trying to say in this paper habitats are the end-all," Arkema said. "What we're trying to say is that they do provide a lot of power in terms of reducing risk of people and property. If they were to be lost, that would require either massive investments and hard infrastructure and engineering approaches, or damages and loss of life."

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500