Fragile Reefs, Dunes Protect Millions on U.S. Coasts

Terrell Johnson
Published: July 17, 2013

Coastal Wetlands

Coastal Wetlands

Coastal wetlands — seagrass beds, mangrove forests and marshes — cover less than 1 percent of the total marine area on the planet, but they play a crucial role in shielding coastal communities from storms. (NOAA)

  • Coastal Wetlands
  • Storm Damage
  • Beach Dunes
  • Rebuilding Reefs
  • Coastal Hazards Data Portal
  • Rebuilding Reefs
  • Storm Damage
  • Restoring Coastline
  • Coastal Hazards Data Portal
  • Coastal Hazards Data Portal
  • Coral Reefs
  • Restoring Coastline
  • Restoring Coastline
  • Storm Damage
  • Maui Shoreline
  • Maui Shoreline
  • Pacific Coastline
  • Beach Erosion

All along the U.S. coastline, millions of people and billions of dollars' worth of real estate rely on nature's defenses -- like coral reefs, coastal forests and beach dunes -- for protection against the impacts of extreme weather and rising seas.

Neglecting these natural defenses could double the number of people at risk in "high hazard" coastal areas, including hundreds of thousands of the poor and elderly, according to a study released this week in the journal Nature Climate Change.

"The natural environment plays a key role in protecting our nation's coasts," said Dr. Katie Arkema, the study's lead author and a Stanford University marine ecologist who works with the Natural Capital Project.

"If we lose these defenses, we will either have to have massive investment in engineered defenses or risk greater damage to millions of people and billions in property."

The study features a first-of-its-kind interactive map of the entire U.S. coastline that details where and how much protection coastal cities and towns get from natural habitats like sand dunes, sea grasses, oyster reefs and mangrove forests, down to a one-square-kilometer resolution.

To create the map, the study's authors calculated what they call a coastal hazard index, which incorporates five different forecasts for sea level rise along the East, Gulf and West Coasts. The map shows the index for every square kilometer along the coasts based on whether natural coastal habitats remain intact or are lost.

Just over two-thirds of the nation's coastlines are protected by natural habitat, the study reports. Today, 16 percent of those areas are classified as "high hazard," home to about 1.3 million people and some $300 billion in residential real estate (commercial property was not included in the study, so the value of property exposed to coastal damage would likely be much higher).

In the future that number could grow to as high as 1.7 million to 2.1 million people, as current models project an increase of between 30 and 60 percent in the number of threatened people and property along the coasts by 2100.

While it's unrealistic to assume that all natural habitats along the U.S. coasts will be lost completely, in many coastal areas like the Mississippi River Delta -- where some 1,900 square miles of wetlands have disappeared since the 1930s -- the losses to date already are immense.

"We wanted to figure out where it is most important to make sure that loss and degradation doesn't happen," Dr. Arkema told, adding that the East Coast and Gulf Coast were most vulnerable -- particularly Florida, New York and California. "These are the places where a lot of people and property have the potential to benefit from natural defense mechanisms."

The study arrives at a time when the U.S. government and many major world cities -- like New York City, London and Chicago -- are looking anew at their plans for dealing with climate change, from protecting their populations against rising sea levels and storm surge to reducing greenhouse gas emissions.

As many cities and countries review these plans, it's becoming clear that natural defenses play a critical role because seawalls and other man-made structures designed to keep out the sea only work up to a point.

"In many cases, though, seawalls are limited as an option because of their on-going maintenance costs and the difficulties in predicting long-term sea level rise or storm scenarios -- witness Hurricane Katrina and Superstorm Sandy," said Dr. Mary Ruckelshaus, one of the study's co-authors.

Protecting existing habitats will require local property owners and governments to work hand-in-hand, she adds. In some areas, that will mean simply preserving the natural barriers already there, while in other places, people will need to adapt and coastal habitats may need to be restored.

"In some cases, that simply means enforcing existing regulation," she said. "In other cases, allowing coastal habitats such as marshes to migrate upslope as sea level rises can mean purchasing easements or properties at higher elevations so the habitats can adapt to rising sea levels," adding that organizations like The Nature Conservancy already are doing this with farmers in many places around the U.S. 

Some coastal habitats will be able to adapt naturally to a changing climate, Dr. Arkema notes, "rather than requiring maintenance and repair like hard infrastructure."

"This doesn't mean coastal habitats are necessarily free," she added. "Keeping these current habitats intact will require some work and some investment in conservation. But conservation is generally cheaper than restoration or construction of hard structures so where we have habitats intact, let's keep it that way."

Read the full study here, or see the coastal hazard interactive map here.

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