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New Map Shows Where Nature Protects U.S. Coast

By Brian Handwerk for National Geographic
7/16/2013 11:49:20 AM

This following is an excerpt courtesy of National Geographic.

Real estate is all about location, and coastal reefs and wetlands now look like especially attractive neighbors.

Americans looking to buy seaside property would do well to study the first ever nationwide map showing how and where natural habitats like reefs and vegetation best protect coastal residents from rising seas and catastrophic storms like last year's Hurricane Sandy. (See "Hurricane Sandy Pictures: Floods, Fire, Snow in the Aftermath.")

Shoreline engineering like seawalls can be effective but also expensive, environmentally undesirable, and a detriment to tourism and seaside recreation. But conserving and restoring nature's own coastal habitats can also help save lives. Now Stanford University's Katie Arkema and colleagues have provided a national map of where natural habitats do most reduce risk to people and property-and where they may need help.

Coastal habitats including marshes, dunes, seagrass beds, mangrove and other coastal forests, kelp forests, oyster beds, and coral reefs help keep waves and storm surge from flooding and eroding coastal property. Coral reefs, for example, can reduce the energy of waves that hit shore by 85 percent.

Some two-thirds of the U.S. coast is currently protected by one or more of these helpful habitats, according to the study.

Coral reefs seen during spring low tides at Sombrero Key Lighthouse. Photograph by Mike Theiss, National Geographic

Mapping a "Hazard Index"

Arkema and colleagues mapped coastal habitats to create a "hazard index" that evaluated every square kilometer of the U.S. coastline under five different scenarios of sea-level rise. The team then added the coast's human geography, illustrating where people and property stood in harm's way with demographic data from the U.S. Census Bureau and property values developed, in part, from a relationship with the online real-estate service Zillow. (See coastline pictures.)

"It's not just about whether habitats are capable of providing coastal protection," said Arkema, a marine ecologist with Stanford Woods Institute for the Environment.

"It's also where they matter for people and for property," she said. "We really wanted to figure out where habitats are reducing exposure and also where those locations overlap with coastal property values and human populations that need to be protected."

When the team modeled U.S. coastlines with these natural protections removed the results were dire, suggesting that the loss of such habitats would double the stretches of coastline now highly exposed to floods and storms and expose an additional 1.4 million Americans to such threats.

"That really surprised me," Arkema said. "It does make sense. We know for example that there are a lot of people in Florida, and that Florida gets hit with a lot of hurricanes, but when I saw that the totals actually doubled I was really surprised."

Peter Kareiva, chief scientist for The Nature Conservancy, said the study was the first of its type to be really proactive.

"With other studies a disaster comes along, say a tsunami, and afterward people collect information and say, 'Here where they left the mangroves intact, people didn't seem to suffer as much.' That's good science but it's after the fact.

"This study takes us in a direction of saying let's be proactive," he continued. "Let's not wait for a storm to happen. Where does natural habitat offer some natural risk reduction before the storm happens?"

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