New Hazard Maps Show Most At-Risk U.S. Communities

Stefan Lovgren
for National Geographic News

February 12, 2008

Places in the United States where people are most vulnerable to natural hazards have become more widespread over the past 40 years, a new map reveals.

The map reflects new research that uses a "social vulnerability index" to rate risk based on factors such as age, race, and socioeconomic status.

Scientists created the index to identify by county which populations may be less able to respond to and cope with natural disasters such as flooding, earthquakes, or hurricanes.

In the 1960s the greatest social vulnerability was centered in the Southwest, while in the 1970s one of the more dominant high-risk regions was the Texas-Mexico border.

Over the next few decades the concentrations of vulnerable people shifted so that there is now a more even distribution across the country.

"Social vulnerability is dynamic, changing over time and certainly across space," said lead study author Susan Cutter, a geography professor at the University of South Carolina.

"Our social vulnerability to natural hazards [overall] has been reduced a little bit, but there are areas where it has increased significantly."

Some of the current high-risk regions include Alaska, the Mississippi Delta, the Rio Grande border area, California's Central Valley, and large urban areas.

A paper describing the study appears today in the Proceedings of the National Academy of Sciences.

Able Response

Today more U.S. citizens live in high-hazard areas—such as earthquake zones and coastal regions prone to hurricanes—than ever before.

But the new study focused exclusively on those people's vulnerability to the natural hazards they might face.

"We initially wanted to quantify social vulnerability to hazards and look at geographic distribution," Cutter said.

"Then we became interested in how [that vulnerability] would change … and how it could help us better prepare for disasters.

"If we know the areas that have a greater likelihood based on social vulnerability, we know where to put additional resources to better prepare for a natural disaster," she added.

Not surprisingly, a community's economic status plays a large role in how well its people may handle a natural disaster.

For example, poverty-stricken New Orleans Parish is rated as highly vulnerable should disaster strike. But wealthier areas such as Charleston, South Carolina, are ranked as less vulnerable.

(Related news: "New Orleans Levees Not Built for Worst Case Events" [September 2, 2005].)

"If you don't have a car and you're told to evacuate, and no provision is given to you to do so, that will affect your ability to respond," Cutter said.

Shifting Risk

In a similar sense, the elderly, children, and people living in mobile homes are especially vulnerable to natural hazards, Cutter said.

The Northern Great Plains region, for example, has become more vulnerable during the past four decades, Cutter said.

"A lot of that is related to depopulation, where the residual populations are increasingly elderly and on fixed incomes, so that their ability to respond to a potential natural disaster is becoming increasingly restricted and therefore vulnerable," she said.

By contrast, the growing affluent areas in Colorado have become less socially vulnerable.

Communities that are reliant on a single-sector economy, such as tourism, are also at risk if their resources are completely wiped out by a natural disaster.

"What this means is that, from an emergency management perspective, I don't think you can assume that all of your resources—both human and financial—should be distributed evenly throughout your area," Cutter said.

"Some communities are perfectly able to handle themselves, while others need additional resources."

Dennis Mileti is a professor emeritus at the Institute of Behavioral Science at the University of Colorado, Boulder.

"Mapping social vulnerability is at least as important as mapping physical vulnerabilities, such as shaking intensity [from earthquakes] and floodplains," Mileti said.

"The impacts of disasters are very much influenced by the people whom the natural events impact," he added.

"Understanding how and why those human differences are distributed is profoundly important for getting ready for dealing with disaster losses."

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