The term “100-year flood” can be misleading. It doesn’t happy once every 100 years, so why is it called that? A 100-year flood is a statistical term for a flood event that has a 1% chance of occurring in any given year. A 1% chance means that in any given year, there is a 1 in 100 chance of a flood of that magnitude happening. It doesn't mean the flood happens exactly every 100 years, as such events can happen multiple times within a century or not for centuries. The term refers to the flood's magnitude or severity and is used in flood risk assessments for insurance and building regulations. Another misunderstanding is that floods bigger than 100-year floods are too rare to be of any real concern. The 1% chance per year accumulates to a 10% chance per decade, a 26% chance during a 30-year mortgage, and a 55% chance during an 80-year human's lifetime. So, the next time somebody says they live in a 100-year floodplain and the last 100-year flood was 3 years ago so they don’t have to worry for another 97 years, use this information to explain the real meaning of a 100-year-flood.
