NB: This failure of statistical logic also shows up in "100 year storm" statistics.
The actual measurement is "storm with a 1% likelihood of occurring in any one year". The odds of that storm occurring in a century is actually about 63%, and of occurring in any ten year period, about 10%.
Add to that the fact that the measurement is based on a storm of a given magnitude (usually total rainfall / precipitation, wind speed, storm surge, etc.) occurring, and small changes in the likelihood of such events can dramatically change the rate at which a storm of a given magnitude is observed. If you live in/near flood-prone areas, keep an eye on, e.g., changes in what are considered flood stages (say, as flood control structures are added or removed), or to likelihoods of events of a given precipitation level or stream height.
The actual measurement is "storm with a 1% likelihood of occurring in any one year". The odds of that storm occurring in a century is actually about 63%, and of occurring in any ten year period, about 10%.
Add to that the fact that the measurement is based on a storm of a given magnitude (usually total rainfall / precipitation, wind speed, storm surge, etc.) occurring, and small changes in the likelihood of such events can dramatically change the rate at which a storm of a given magnitude is observed. If you live in/near flood-prone areas, keep an eye on, e.g., changes in what are considered flood stages (say, as flood control structures are added or removed), or to likelihoods of events of a given precipitation level or stream height.