Louisiana flooding: What is a 500-year flood and why is it happening so much?

Published: Wednesday, August 17, 2016 @ 8:23 AM
Updated: Wednesday, August 17, 2016 @ 8:27 AM

As  of Wednesday morning, 11 people have died and more than 40,000 homes have been damaged in ongoing flooding  in southeastern Louisiana.

Up to two-and-a-half feet of rain that swelled rivers and swamped the area in and around Baton Rouge, La., has led the National Oceanic and Atmospheric Administration to classify the flooding as a once-in-every-500-years event.

Obviously, by definition, the events are rare – except this is the eighth time one of the 500-year events has happened in the United States in a little more than 12 months.

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Six states – Louisiana, Texas, West Virginia, South Carolina, Maryland and Oklahoma --  have all had unprecedented rainfall events that, according to NOAA research, they should have only had a less than one percent chance of experiencing in any given year. 

So what is a 500-year flood and why are they happening more frequently? Here’s a quick look at what the historic rainfall means.

What is a 500-year flood?

The U.S. government, when creating the National Flood Insurance Program, used a measure called the 1-percent annual exceedance probability flood (AEP) to estimate the chance of repeat flooding of a certain level  in a certain area. The AEP defines a flood that, statistically, has a 1-in-100 chance of  being equaled or surpassed in any one year, thus the term “100-year flood” was born. The 500-year flood” is equal to an AEP of 0.2 percent, or a 1-in-500 chance an area will see a repeat of flooding at a certain level. 

In some areas of Louisiana, the flooding is being classified as a 1000-year-event – or an 0.1 percent chance of seeing flooding like that in any given year.

How are flood risks determined?

Scientists and engineers take annual measurements of the strength of the flow of a body of water and the peak height of the water as recorded by devices called streamgages. These devices are placed in spots along a river. They use those numbers, collected over time, to determine the probability (or chance) that a river will exceed those measurements during any given year.

Does a 500-year flood really mean that a flood of that type happens only once every 500 years?

No, not exactly. We are talking math. The term means  that, statistically, there is a 1-in-500 chance that an area will have a large flood in any given year. You could have a large flood two years in a row, but, chances are, you won’t. 

Why are we seeing eight such floods in the U.S. in a little over a year then? Does climate change have anything to do with it?

Climate scientists sure think it does. Many say they believe that global warming has everything to do with it and say we can look forward to more of these events. They have warned that warming temperatures on both land and sea, and the build-up of moisture in the atmosphere, will inevitably cause more large flooding events.

“We have been on an upward trend in terms of heavy rainfall events over the past two decades, which is likely related to the amount of water vapor going up in the atmosphere,” said Dr Kenneth Kunkel, of the Cooperative Institute for Climate and Satellites, told The Guardian.

“There’s a very tight loop – as surface temperatures of the oceans warm up, the immediate response is more water vapor in the atmosphere. We’re in a system inherently capable of producing more floods.”

David Easterling told The New York Times that the flooding “is consistent with what we expect to see in the future if you look at climate models. Not just in the U.S. but in many other parts of the world as well.” Easterling is a director at the National Centers for Environmental Information, which is operated by the NOAA.

Sources: NOAA; The New York Times; The Guardian; The Associated Press; The National Weather Service

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Paul McCartney reflects on John Lennon at March for Our Lives rally

Published: Saturday, March 24, 2018 @ 3:21 PM

NEW YORK, NY - MARCH 24:  Sir Paul McCartney joins thousands of people, many of them students, march against gun violence in Manhattan during the March for Our Lives rally on March 24, 2018 in New York, United States.  (Photo by Spencer Platt/Getty Images)
Spencer Platt/Getty Images
NEW YORK, NY - MARCH 24: Sir Paul McCartney joins thousands of people, many of them students, march against gun violence in Manhattan during the March for Our Lives rally on March 24, 2018 in New York, United States. (Photo by Spencer Platt/Getty Images)(Spencer Platt/Getty Images)

Music legend Paul McCartney participated in the March for Our Lives rally in New York City Saturday.

When asked by a CNN reporter what he hoped could be accomplished by the movement, McCartney pointed to his shirt, which had the message, "We can end gun violence" printed on it.

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"One of my best friends was killed in gun violence right around here, so it's important to me," McCartney said.

McCartney was referring to his former Beatles bandmate, John Lennon, who was shot and killed in New York City in 1980 by Mark David Chapman. Lennon was 40 years old.

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Naomi Wadler, age 11, delivers powerful message at March for Our Lives rally

Published: Saturday, March 24, 2018 @ 2:33 PM

VIDEO: Scenes from March for Our Lives Rallies

An 11-year-old girl delivered a powerful message about gun violence at the March for Our Lives rally Saturday in the nation's capital.

Naomi Wadler, a fifth-grader at George Mason Elementary School in Alexandria, Virginia, focused her speech on the gun violence that African-American women face, and how often their stories go untold.

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"I am here today to acknowledge and represent the African-American girls whose stories don't make the front page of every national newspaper, whose stories don't lead the evening news," Wadler told the crowd.

"For far too long these names, these black girls and women have been just numbers. I'm here to say 'never again' for those girls, too," Wadler said.

Wadler rejected the notion that she was too young to understand the issue. "People have said that I am too young to have these thoughts on my own. People have said that I am a tool of some nameless adult. It's not true," Wadler said.

"We know life isn't equal for everyone and we know what is right and wrong," Wadler said.

Her speech quickly began trending on Twitter.

Wadler also helped organize a walkout at her school to protest gun violence on March 14, the Fairfax County Times reported.

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12-year-old boy missing after getting on wrong school bus has been found near his home

Published: Friday, March 23, 2018 @ 5:58 PM

A 12-year-old boy has been missing for two days after getting on the wrong school bus at a metro Atlanta middle school.
A 12-year-old boy has been missing for two days after getting on the wrong school bus at a metro Atlanta middle school.(Pixabay)

Update March 23, 2018 8:50 EST: A missing Atlanta area middle schooler has been found safe.

Anthony Randolph III disappeared Wednesday after getting on the wrong bus at his school in DeKalb, Georgia.

Investigators have been searching for the boy for two days and found him Friday at a gas station not far from his home, police said.

Police have not released the details on where the boy has been and how he was found. 

(Previous story)

12-year-old boy disappeared after getting on the wrong school bus on his way home from middle school in metro Atlanta.   

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Anthony Randolph III disappeared Wednesday after boarding the wrong bus at Redan Middle School in DeKlab County, police said.

Investigators said the boy got off the bus two miles away from his home. 

He wasn’t supposed to be on that bus and school officials said they are working to figure out why the bus driver didn’t take him back to school.

“We need you home Anthony, fast, please,” the child’s father, Anthony Randolph Jr., said.

Randolph wiped away tears as he begged anyone with information on the disappearance of his son to come forward.

>> Related: Girl shot in Maryland school shooting taken off life support, dies

A search is underway as police continue investigating the boy’s disappearance.

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March for Our Lives rallies take place across the globe

Published: Saturday, March 24, 2018 @ 9:07 AM
Updated: Saturday, March 24, 2018 @ 3:25 PM

VIDEO: Scenes from March for Our Lives Rallies

Marches and rallies were held in the U.S. and around the world Saturday as part of the March for Our Lives event. The student-led movement seeks legislative action on the issues of gun violence and gun control in response to a series of deadly school shootings.

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The movement is being led by student survivors of the Parkland High School mass shooting in Florida on Feb. 14, in which former student Nikolas Cruz, 19, killed 17 people and injured dozens. 

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