Rising sea levels and extreme weather put 16% of U.S. coastlines at "high-hazard" risk and the number of threatened residents could double if natural habitats -- sand dunes, coral reefs, sea grasses, mangroves -- aren't protected, Stanford University researchers say in a study today.
The study, noting that 23 of the 25 most densely populated U.S. counties are coastal, comes as U.S. and local officials are looking at "hardening" shorelines with billion-dollar sea walls and other projects in the aftermath of Superstorm Sandy, which devastated the mid-Atlantic coast last October. It says maintaining habitats may offer a simpler, cheaper alternative in some areas.
"If we lose these defenses, we will either have to have massive investments in engineered defenses or risk greater damage to millions of people and billions in property," said lead author and Stanford scientist Katie Arkema in announcing the findings, published in the peer-reviewed journal Nature Climate Change. She says reefs and dunes play critical roles in places such as Hillsborough and Monroe counties in Florida and Brooklyn in New York.
To show where habitats offer the most protection per square kilometer, the researchers developed a hazard index based on the existence (or not) of natural habitats, residential property values, population, erosion and five federal scenarios for sea level rise.
They found good and bad news. On the plus side, natural habitats now protect two-thirds or 67% of U.S. coastlines. Yet the 16% of high-risk coastlines that are within a kilometer of the shore are home to 1.3 million people and $300 billion in residential property. The study says sea level rise, a result of climate change's rising temperatures, will increase the number of threatened people 30% to 60% by the year 2100.
"This study is a pretty significant advance over what's been done before," says Virginia Matzek,a restoration ecologist at Santa Clara University in California. She says prior research has looked at individual pieces, such as the role of habitats or the areas most at risk of sea level rise, but this is the first to synthesize them. She says the findings are conservative, noting the authors assumed current storm frequency, although storms are expected to get more frequent.
"If I were a county planner, I'd be all over this," she says. She adds that more research is needed, however, because current data is limited.
Peter Kareiva, chief scientist at The Nature Conservancy and one of the study's co-authors, says data show whether an area has natural habitat but not its type, extent or exact location. He says it makes a difference whether marsh or reef is 10 feet or 100 feet offshore, arguing the federal government needs to invest in mapping coastal habitats.
"We have the Human Genome. What about the Earth Genome?" he asks, saying habitats could reduce the need for costlier solutions and offer other benefits such as recreation, fish nurseries, water filtration and erosion control. "It costs a ton of money to build a sea wall, and a sea wall does one thing only. Habitats do many."
The study says the East and Gulf coasts are more vulnerable to sea level rise than the West coast. It says while habitats may protect some areas, "sea level rise will overwhelm" them in others, so additional measures are needed. It was compiled by Kareiva and eight Stanford researchers who are working with the Natural Capital Project, a partnership of scientists focused on nature's benefits.