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Ellicott City's "1,000-year" Flood Explained

Was the historic flood a once in a lifetime event?
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Posted at 9:51 AM, Aug 04, 2016
and last updated 2018-05-28 14:13:52-04

When meteorologists talk about a "100-year flood" or a "1,000-year flood," they don't actually mean that the event will happen once every 100 or 1,000 years. Rather, it is a statistical way of expressing the probability of something like this happening in a given year. The chart below is from the USGS (United States Geological Survey), explaining the meaning of these floods.

Therefore, a “1,000-year flood has a 1 in 1,000 or .1 percent chance of happening in any year -- but the event does not have to be in 1,000 year intervals.
 

Within the science of climatology and meteorology, these floods are viewed statistically, as in a 1 in 100 or 1 in 1,000 chance of happening. So in reference to the Ellicott City flood over the weekend, there was only a 1 in 1,000 chance of that happening, or .1 percent. This explains why some Marylanders recall Ellicott City being hit by bad floods before 2016's "1,000-year flood". If anything - it's still impressive that this happened again so soon knowing these odds.

**The National Weather Service has a great report available on this topic for the flood that happened in 2016. The link is listed below.**

http://www.weather.gov/lwx/EllicottCityFlood2016

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