Why do we have 100-year floods more often than once every century?
The USGS has published a new poster explaining the origin of the idea of the "100-year flood," and why it's been so misunderstood. They are now urging that instead, we use the annual exceedance probability (AEP) terminology which is defined as "the 1-percent AEP flood has a 1 in 100 chance of being equaled or
exceeded in any 1 year.”
They propose we should discuss the “1-percent AEP flood” as opposed to the “100-year flood.”
Frankly, I have a hard time expecting the public and news media making this change, even if the scientific and technical communities adopt it.