Mar 1, 2017
CURRENTS: Muddy Waters: Defining the 100-Year Flood
When used properly, the term “100-year flood” really means there is a 1-in-100, or 1 percent, chance of a flood occurring in a certain area in any given year. Given that probability, that flood is likely to occur, on average, once every 100 years over an even longer period of time. Similarly, you would call a flood with a 1-in-500, or 0.2 percent, chance of occurring every year a “500-year flood.”