Use of '100 Year' and '500 Year' Flood Terms Misleads Insureds, Say Officials

July 2, 2008

Fifteen years ago, after the Midwest was swamped with what was pronounced a "100-year'' or even a "500-year'' flood, some folks figured they would never again see such a disaster in their lifetime. Some even dropped their flood insurance.

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Big mistake.

Now, with the region struck by a supposedly once-in-a-lifetime flood for the second time since 1993, some scientists and disaster officials say the use of terms like "100-year flood'' should be re-evaluated because they are often misunderstood and can give the public a false sense of security.

"We, the United States Geological Survey, almost need to quit using the term '100-year flood,''' said hydrologist Gary Wilson with the USGS Missouri Water Science Center in Rolla, Mo. "It could happen twice a year, if you're unlucky.'' Or 200 years could go by without a 100-year flood, he said.

Villanova University professor Robert Traver, who specializes in storm water management, was more succinct: "Whoever invented that term should be shot.''

Several government scientists say they have tried to move away from using the terms, yet they also say they routinely fall back on the labels as shorthand for measuring a flood's severity.

Editor's Note: For more information on flood zones and their meanings, see commentary "Flood Damage Not Limited to 'Flood Zones'."