What Is a 500 Year Storm

(WHSV) – The term “500-year flood” is used commonly when an area sees historic flooding. … A 500-year flood is defined as a 0.2% chance of seeing a significant flood event. This probability averages out to seeing this kind of flood every 500 years but there’s a problem with that probability.

What is a 100-year hurricane?

A 100-year storm refers to rainfall totals that have a one percent probability of occurring at that location in that year. … [1] In other words, there is a 1 in 100 or 1% chance that a storm will reach this intensity in any given year. Likewise, a 50-year rainfall event has a 1 in 50 or 2% chance of occurring in a year.

What is the difference between a 100 year flood and 500 year flood?

A 100 year flood is the level of flooding that has a 1% chance of occurring in any given year, and has an equal chance of occurring every year, regardless of whether or not it occurred in previous years. … Similarly, a 500 year flood is flood levels that have a 0.2% chance of occurring in any given year.