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WHEN HURRICANES THREATEN


Thousands of homes lie abandoned under a darkening sky. Traffic clogs the roads on a biblical scale. Cars overheat, and so do the people inside. They know as they inch along that an alarmingly few miles away, rising from the sea like a frothing monster, a killer hurricane is bearing down on them.


Eye in the Sky


All authorities agree that the best defense against a major tropical storm is to be somewhere else. But mass evacuations—like the one that emptied many coastal areas in the southeastern United States threatened by last year’s Hurricane Floyd—bring their own terrors. Homes are left unprotected, confusion reigns, and in some cases safety is a factor, especially for the elderly and infirm.

This year the disruptions in one Florida county may be more easily borne when a hurricane comes knocking because of a technological breakthrough. Over a roughly three-month period last winter, scientists equipped with laser equipment about the size of several large suitcases flew over about 25 miles of Broward County coastline, including the Fort Lauderdale area. They gathered data that allows 3-D mapping of terrain more quickly and accurately than ever before imagined.

As a result, county officials have drastically reduced the areas they will order evacuated when the next storm strikes. The revised evacuation plans call for the temporary relocation of 130,000 county residents in case of a major threat, compared to the previous target of 290,000.

“We’ve been able to roughly cut in half the number of people who will have to leave,” says Glenn Margolis, grants and mitigation administrator with Broward County’s Emergency Management Division. “This will prevent jeopardizing lives and will allow more people to concentrate on protecting themselves at home.”

The new maps were made possible by a combination of laser technology, Global Positioning System (GPS) satellites, and powerful computer software that allows millions of bits of information to be combined. These maps show precisely which areas are at risk from storm surge and secondary flooding from torrential rainfalls—and which ones will be left high and more or less dry.

“This system can return absolute elevations of the ground surface accurate to six inches (15 cm),” says Stephen P. Leatherman of Florida International University’s International Hurricane Center, which owns the hardware that was used by Broward County. That compares to an accuracy of plus or minus five feet (1.5 meters) in standard topographical maps the county had relied upon previously.

“The terrain around here is so flat that five feet can make the difference between being underwater and not,” says Margolis.

The U.S. $250,000 price tag for the project included the fly-overs, the computer numbers-crunching and the map-making itself.

The gadget, an Optech 1012G ALTM (Airborne Laser Terrain Mapping), is manufactured by a company in Toronto and sells for about U.S. $1 million. The International Hurricane Center has also used the technology for several other projects as well, including assessing damage caused by Hurricane Floyd around Vero Beach, Florida.

This year the center hopes to use its equipment to make before-and-after images of hurricane-damaged areas for the purpose of assessing beach erosion and damage to dunes. Also on the drawing board is a US $2.5 million, three-year project to collect data from more counties in southern Florida for the purpose of refining flood maps.

“The basic technology has been around for a while,” according to the center’s Dean Whitman. “But it’s only over the last few years you’ve started to see off-the-shelf commercial systems like this available. Now things have really come together with computer and laser technology to make this a practical and cost-effective solution. It’s a hot area in remote sensing applications.”

In Broward County, officials have made their new maps available to the public and are encouraging residents to make plans now for what to do if a hurricane approaches. Structures judged vulnerable to high winds, such as mobile homes, will be evacuated regardless of their susceptibility to storm surge and flooding.

Now, all they can do is wait.

Eye in the Sky is a weekly series that brings you the story behind the headlines using satellite imagery, remote sensing, aerial photography, and maps. This feature is developed by National Geographic News with the sponsorship of the National Imagery and Mapping Agency (NIMA) and Earth-Info. Check out maps and imagery at http://www.earth-info.org.



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More Information
•  Better topographical maps will allow more accurate assessment of the dangers of storm surge as well as the other great threat from hurricanes: inland flooding due to torrential downpours.
•  More people have died from inland flooding over the past 30 years than from storm surge.
•  Of the 56 people who died in Hurricane Floyd, all but six drowned in flooded areas far from the coast.
•  Inland flooding can threaten communities located hundreds of miles away from a hurricane’s landfall.


More Information

FLEEING FLOYD

In what some have called the largest peacetime evacuation in U.S. history, approximately 1.5 million people fled coastal areas of Florida, Georgia, North and South Carolina, along with parts of Virginia and New Jersey, during last year’s Hurricane Floyd.

“It became a traffic nightmare for those who were on the highway,” recalls Mary Hudak of the U.S. Federal Emergency Management Agency. “Very short trips took ten times longer than they should have. People couldn’t find gas stations and other routine facilities along the way: The owners were evacuating themselves.”

Many coastal Georgians traveled as far inland as Atlanta—only to find no hotel vacancies and overcrowded shelters in the capital. Some continued on as far as Chattanooga, Tennessee, 350 miles (560 km) from the coast.

Georgians trying to escape north on I-95 found themselves stacked behind cars from South Carolina—who were inching along bumper-to-bumper behind North Carolinians headed into Virginia.

To add to the misery and confusion, once people left the reach of local radio stations, they could no longer get updated information about what was going on back in their communities.

Based partly on a behavioral study conducted by FEMA after the hurricane among some 7,000 coastal dwellers, the agency this year has launched an education program to urge people to have an evacuation plan based on knowing whether they are at risk. Depending on the elevation of an area, storm surge and inland flooding may not be a problem—in which case authorities advise staying at home.

“The rule is, run from the water, hide from the wind,” says Hudak. “And have a plan if you do leave. Going ten miles away might put you in just as safe an area as going 100 miles.”

Hurricane Floyd “showed us very clearly that people will take heed of these very dramatic storm warnings,” says Hudak. “What we need for them to do is plan better in advance to take the appropriate protective action.”