What a 100-year flood really means
We’ve all heard the term “100-year flood” — but it might not mean what you think.
CHARLOTTE, N.C. — When forecasters warn about a 100-year or 500-year flood, it doesn’t mean it only happens once every century.
A 100-year flood has a 1% chance of happening in any given year. A 500-year flood? Just a 0.2% chance.
But that doesn’t mean it can’t happen twice in a short time.
In fact, Houston saw three 500-year floods in just three years — including Hurricane Harvey.
Thanks to climate change, extreme rain is becoming more common. Warmer air holds more moisture, which means heavier storms and more flooding.
Scientists say we’ve already seen a clear shift in how often these big rain events occur — especially over the last 30 years.
So, while the math helps explain risk, the climate is rewriting the rules. And the term “once in a lifetime” may not mean what it used to.
For the latest breaking news, weather and traffic alerts that impact you from WCNC Charlotte, download the WCNC Charlotte mobile app and enable push notifications.
About The Author
