When 1-in-100 Year Floods Happen Often

Posted on: May 9th, 2019 by Leslie_Zucker

The “100-year flood” can happen a lot more often than every 100 years. National Public Radio (NPR) just tried to clear up the confusion – listen or read the story here. Many people assume if they’ve experienced a 100-year flood it won’t happen again for another 99 years, but this is not the case. The term “1-in-100 year flood” means there is a 1% chance a flood will happen each year. If it happens this year, there is still a 1% chance it will happen next year. Also, every other sized flood could happen in a year, they are just more or less likely.

The hundred-year flood term was adopted by FEMA to designate a zone where flood insurance is required with a federally backed mortgage. The 100-year floodplain is an area where flood risk is higher, but it’s not the only tool, and maybe not the best way to determine your flood risk. It’s better to think in longer timeframes.

As the NPR story states, it’s better to know this fact – there is a 26% chance the 100-year flood will happen over the course of a 30-year mortgage. If you live your entire life in the flood zone, you are likely to experience a big flood.