The Truth about 100-Year Floods

 Whenever a strong hurricane or storm causes significant flooding, there is often talk of a 100-year flood. When people hear this term they think a flood of that magnitude occurs once every hundred years, so they should be safe from harm for the next hundred years. Unfortunately, some base their decision to buy flood insurance on this false belief, putting them at risk of a catastrophic loss.

 The reality of this is different. It involves frequency analysis and statistical probability. In order to determine the frequency of floods of a given level, scientists create a history of the area. Generally, scientists start with a minimum of ten years of information. The longer the record, the better and more accurate predictions. They look at the frequency of different size floods and the average number of years between them in order to develop the probability of a given size flood in any given year.