Terms like '100-year hurricane' create a false sense of security
The disconnect between the common understanding and the scientific meaning is leading local and state officials to seek clearer verbiage for discussing hurricanes, floods and the levels of protection that the government provides.
By Sheila Grissett
OpEd: Educating people on risk
NEW ORLEANS — When the Army Corps of Engineers promises to protect southeast Louisiana from flooding triggered by a "100-year hurricane," the all-too-common assumption is a storm that will occur only once a century.
But that misunderstanding can contribute to a world of bad decisions, from homeowners feeling secure enough to drop flood insurance to members of Congress refusing to finance a higher level of protection.
In reality, "100-year hurricane" is merely shorthand -- poor shorthand, in the view of a growing number of community activists, scientists and government officials -- for a storm that has a 1 in 100 chance of occurring in any given year. Such a storm could hit every year, or not at all for a century.
In this respect, storm prediction is akin to flipping a coin. The chances of the coin coming up heads are always 1 in 2, although it's quite possible to get heads several times in a row.
Now, the disconnect between the common understanding and the scientific meaning is leading local and state officials to seek clearer verbiage for discussing hurricanes, floods and the levels of protection that the government provides.
"We must settle on a new way of explaining risk, a new vocabulary that laypeople can understand," said John Barry, a commissioner for the Southeast Louisiana Flood Protection Authority-East who has written extensively on Mississippi River flooding.
"The phrase '100-year-flood' doesn't communicate to the public or to policymakers the real risk of flooding. They think it means a flood that occurs once every 100 years, when in fact, there's something like a 60 percent chance of experiencing it in your lifetime."
The Southeast Louisiana Flood Protection Authority-East has also added its voice to a chorus challenging the federal government to devise a more easily understandable explanation of risk. The authority's plea followed a similar one from the state's Coastal Protection and Restoration Agency.
The Federal Emergency Management Agency began moving some years ago to redefine the "100-year storm" as "a statistical event that has a 1 percent chance of occurring each year." In doing so, FEMA acknowledged that the lexicon of engineers and statisticians wasn't informing the public at large.
"Mark Twain said the difference between the right word and the wrong word is the difference between lightning and lightning bug," Barry said. "Residents need to understand . . . members of Congress need to understand that the risk of a '1,000-year flood' occurring in the average life span of an individual is well over 5 percent."
More recently, FEMA has tried to clarify the probability of a 100-year flood by saying that it has about a 26 percent chance of occurring during the life of a 30-year home mortgage. That's about triple the risk of a fire during that same period.
But that still "fails to communicate either the real risk of a greater flood or any sense of the catastrophic community-wide impact" of such a disaster, according to the resolution adopted by levee authority commissioners.
Barry said the key players in any potential change -- such as FEMA, the Army Corps of Engineers and the National Weather Service -- have not agreed on a new metric.
"I don't have a solution, but someone has to take the lead in actually making a change," Barry said. "The entire flood community is behind this, but someone has to make it happen."
Similarly, authority commissioner Tom Jackson pointed out that the weather service is still using the Saffir-Simpson category scale to rate hurricanes, a methodology that the corps and FEMA abandoned after Katrina. The scale historically is based on wind speed but also includes a generalized description of hurricanes' other damaging effects, including the heights of storm surge.
Along the Gulf Coast, a Category 1 or 2 storm was one that didn't worry most people because their accompanying surge was believed to be a threat only outside levees. A Category 3, depending on forward speed, was known to create surge high enough to top levees and trigger evacuations. Category 4 and 5 storms were understood to have catastrophic potential.
That characterization died for most federal agencies after Katrina. With Category 3 winds but a Category 5 storm surge on the eastern edge of New Orleans, it killed more than 1,500 people and caused billions of dollars' worth of damage.
Research after the storm found that Katrina's surge height was governed by the radius of its hurricane-force winds, which did not necessarily follow the Saffir-Simpson categories.
For example, Hurricane Camille in 1969 was a Category 5 storm based on its wind speed and raised a 23-foot surge when it went ashore in Mississippi. But its hurricane-force winds extended only 10 miles from its eye.
Katrina, however, created a 26-foot surge along a much wider swath of the Mississippi Coast -- with at least one report of water 32 feet high -- while having only Category 3 wind speed. That's because its hurricane-force winds extended 75 miles from its center, and it had been at Category 5 strength only 12 to 18 hours before landfall.
"I don't have an answer either," said Jackson, an engineer. "But the weather bureau is still using 'category' storms. "What are they going to tell us in the Gulf now?"
Actually, the National Hurricane Center is studying ways of updating or replacing the Saffir-Simpson scale. In the aftermath of Katrina, it has played down the surge portion of the scale. Instead, the center has begun running maps predicting surge heights for specific storms along specific sections of coastlines 24 hours in advance of a hurricane's predicted landfall.
Searching for the right words
The levee authority sent its resolution seeking a new vocabulary to the corps; FEMA; the National Oceanic and Atmospheric Administration, which includes the National Weather Service; and the National Research Council, whose members have said they will help fashion a new terminology.
"Right now, people are not only not being informed," Barry said. "They are being misled."