Seth Wang / AP File
Foundations and pilings are all that remain of brick buildings and a boardwalk in Atlantic City, N.J., on Oct. 30, 2012, after they were destroyed by Superstorm Sandy.
The percentage of the U.S. population living in counties adjacent to coastline has reached nearly 40 percent in recent years, meaning more of us are exposed to extreme — and extremely costly — coastal storms such as Sandy and Isaac, according to a government report released Monday.
These coastal counties account for less than 10 percent of the U.S. land area, excluding Alaska, meaning that this growing population is packing into a finite amount of space, one that's increasingly threatened by rising seas, storm surge flooding and damaging winds.
"The real issue is the density, the density is growing enormously," the report's editor, Kristin Crossett of the National Oceanic and Atmospheric Administration (NOAA) National Ocean Service, told NBC News.
The density in coastal counties is more than six times greater today than corresponding inland counties and that density is forecast to grow faster than the country as a whole. If the current trends continue, the report notes, the U.S. coastal population will reach 134 million in 2020, up from 123 million in 2010.
"The costs of natural disasters are increasing exponentially," Mike Beck, lead scientist with The Nature Conservancy's Global Marine Team, told NBC News.
Coastal counties are the regions at the highest risk from natural disasters, "and we, the rest of the U.S. public, are underwriting the risks for the people who live in those areas," he added. "That's why, for example, the national flood insurance protection program is in as deep as debt as it is."
Beck noted that over the past several decades more than 16,000 properties in Florida have experienced repetitive losses under the insurance program, meaning that taxpayers have paid more than once to help them rebuild. More than 1,000, he said, have received help four or more times.
It's not all beach houses and waterfront condos, either. Many of the properties in direst need of assistance are owned by people who can't afford to move. Although poverty in coastal counties is about equal to poverty in landlocked parts of the U.S., those who live below the poverty line often find themselves in low-lying areas most vulnerable to storm damage.
"The land that is cheapest in coastal counties is the stuff that is most highest risk, that is regularly flooded," said Beck. "That is where we have our poorest populations."
The population numbers and trends outlined in the new National Coastal Population Report — which NOAA released with the U.S. Census Bureau — should help guide policymakers who shape regulations governing coastal development, the government agency noted.
The Nature Conservancy, for example, is spearheading a program on coastal resilience that advocates things such as protecting coastal wetlands from development and the rebuilding of natural defenses, such as oyster reefs along the Gulf Coast.
Wetlands and oyster reefs, he noted, serve as the first line of defense against oncoming storms and are some of the natural features that attract people to the coast in the first place.
"You might say people love the coast almost too much," Beck said, but "we can reduce risk to people and property and our overall national budget by building more sensibly."
John Roach is a contributing writer for NBC News. To learn more about him, check out his website.