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Millions of Homes Vulnerable to Storm Surge, Rising Seas

By Evan Lehmann, E&E reporter
7/27/2014 4:40:52 AM

More than 6.5 million homes in the United States are threatened by storm surge as exposure to loss is increasing from rising seas and expanded development on coastlines vulnerable to hurricanes, according to a new study.

The research finds that those properties represent $1.5 trillion in potential rebuilding costs with the most severe effects possible in Florida, which faces up to $490 billion in damages to homes.

New York, Louisiana and New Jersey all carry exposures above $130 billion. Together, they face damages that could reach $477 billion if every home susceptible to storm surge was destroyed, according to the research by CoreLogic, a company that analyzes property values for insurers.

The firm identifies sea-level rise as a looming contributor to climbing damage from storm surge, but its experts aren't sure where those losses will occur or how large they'll be.

"As that [sea-level rise] occurs, we're going to see areas that were currently and previously not in a storm surge risk area, those are increasingly going to become risk areas," Thomas Jeffery, the firm's senior hazard scientist, said in an interview. "So we're going to see people who really didn't think they were at risk of this being the ones that in the future potentially are.

(Credit: Flickr/.Martin.)

"We know that there's going to be change. We're just not sure how much change and how quickly," he added.

Storm surge occurs when hurricane-strength winds pile a huge mound of ocean water at the front of a storm. It generally moves at the same speed of a hurricane, perhaps 10 miles an hour, and can overtake a shoreline with devastating force. Each cubic yard of seawater weighs more than 1,700 pounds, or nearly a ton. A 1-foot surge can wash cars off a roadway.

Although the Gulf Coast is more prone to landfall hurricanes than the East Coast, the potential losses in Atlantic states are nearly twice as large, at $950 billion.

"This discrepancy can be attributed to several factors, including the concentration of homes along each coast and the higher-than-average reconstruction values associated with the large metropolitan areas that dominate the central and northeast shorelines," the study says.

Federal flood zones understate surge damage

The analysis takes several factors into account, including the differences in each state's population, the rate of residential development, length of coastlines and geographic factors like the slope of the shoreline. For those reasons, a state like Texas has a high number of homes at risk from surge, at 434,000, but a much lower financial exposure ($77 billion) than more expensive areas. New York state on the other hand has 467,000 homes at risk valued at $182 billion.

The East Coast's risk to flooding was exposed in 2012 when Superstorm Sandy created a storm surge of 12½ feet at Kings Point, N.Y., and a 9-foot surge at the Battery. A surge is the height of water above tide levels.

In 2008, Hurricane Ike produced a surge of up to 20 feet along the Bolivar Peninsula of Texas, contributing to the storm's damage of $24.9 billion, according to the National Hurricane Center. Hurricane Katrina created a surge of between 25 and 28 feet in 2005, and Hurricane Isabel sent an 8-foot surge onto the shores of the Chesapeake Bay in 2003.

The study only looks at residential homes, but public infrastructure is also imperiled. A 23-foot surge along the Gulf Coast could inundate 67 percent of the region's interstates, 29 airports, nearly half of all the area's rail lines and every port, according to the National Hurricane Center.

CoreLogic's research also points to a potential hazard created by the federal government. Most homes with a 1 percent annual chance of flooding are required by their mortgage lenders to enroll in the National Flood Insurance Program. The study says that many homeowners outside flood zones identified by the Federal Emergency Management Agency might erroneously believe they're safe from inundation, when in fact their homes could be ruined by a storm surge.

The study found that 86 percent of flood-prone properties in Virginia Beach, Va., lie outside the federal flood zones, the most in the United States. It's 85 percent in Philadelphia, 76 percent in Jacksonville, Fla., and 74 percent in Boston.

"People in those properties may not realize that they have a risk of flooding because they're not in that FEMA flood zone. But in actuality they certainly do," Jeffery said.

He also noted that the federal flood program, which is about $18 billion in debt, could experience unanticipated exposure to loss if a substantial number of those homeowners purchase flood insurance before a large storm surge occurs.

Reprinted from ClimateWire with permission from Environment & Energy Publishing, LLC. 202-628-6500.

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