Jul 1, 2014 7:33 PM by Akeam Ashford

What Does "100-Year Flood" Even Mean?

Living close to the coast, South Louisiana homeowners often have to worry about floods and quickly-rising water.

The National Weather Service uses "50" and "100-year" flood data to calculate the percentage of rainfall in any given area.

In Lafayette, the largest one-day total was almost 20 inches of rain in August, 1940 during a category two hurricane. That event still holds the record as the wettest tropical system in state history.

"I think we've done a disservice by calling it a 100-year flood, when actually it means there's a one percent chance of that flood happening in any given year," said Jonathan Brazzel, hydrologist with the National Weather Service.

Brazzel said the number '100' refers to the collection of flood data over a 100 year period.

"That is the risk that we are willing to take as a society for flooding. It actually has a lot to do with mortgage rates," said Brazzel.

Brazzel said most people have a 30-year mortgage on their home. Based on a mathematical equation, he said those homeowners can expect about a 26 percent chance of seeing a 100-year flood happen.

That percentage or risk is then used by the federal government to determine flood insurance rates.

"I tell folks all over the state, the best buy a property owner can make in the insurance market place is the federally subsidized insurance program," said Jim Donelon, Insurance Commissioner of Louisiana.



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