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.
