See the path of destruction left by a major flood in historic downtown Ellicott City, Maryland. Rushing waters took the lives of two people after tearing away streets and ripping apart buildings.

The rainfall that caused the devastating flash flood Ellicott City, Md., Saturday evening, killing two people, was a 1-in-1,000 year weather event, meteorologists said.

The storm dumped 6.5 inches of rain on Ellicott City in only about 3 hours, with 5.5 inches falling in just 90 minutes, the National Weather Service said. One nearby spot recorded 8.22 inches, amounts that weather service meteorologist Greg Carbin called “off the charts.”

Ellicott City picked up almost twice its monthly average rainfall of 3.5 inches Saturday night.

The small town’s main street turned into a raging river, carrying away cars and other debris and forcing dramatic rescues of people trapped in the flood. The bodies of two victims were found early Sunday.

The flood also tore away portions of the street and many storefronts, leaving the town in a shambles.

Flooding destroyed parts of Ellicott City, Md. overnight. (Photo: WUSA)

The 1-in-1,000-year rain event is a statistical way of expressing the probability of it happening in any given year in a given location, according to NOAA’s National Center for Environmental Information. It does not mean that it will happen once every 1,000 years.

A “100-year” event has a one in 100 or 1% chance of happening in any given year while a “1,000-year” event has a 0.1% chance of happening in any given year.

There can 1-in-1,000 year flood events, but that was not necessarily the case in Ellicott City: This was a 1-in-1,000-year rain event.

Coincidentally, the all-time world record for a one-minute rainfall happened in Maryland 60 years ago, according to the World Meteorological Organization. On July 4, 1956, 1.23 inches of rain fell in Unionville, Md., which is located in the state’s Eastern Shore region.

The meteorological cause of Ellicott City’s epic flood was complex, a mash-up of high humidity, unstable air, southerly wind flow, a nearby warm front and other factors as noted by the Washington Post’s Capital Weather Gang.

As for considering man-made climate change as a contributing factor, it is true that 71% of heavy rain events have increased in the northeastern U.S. (including Maryland) between 1958 and 2012, according to the National Climate Assessment. But overall, extreme rainfall is not one of the weather events that can be linked to climate change with a high level of confidence, the most comprehensive report on the subject said earlier this year.

But other “human-caused” factors have to do with land use and storm water management, as meteorologist Marshall Shepherd points out in Forbes. He said that there are more “urbanized impervious surfaces” such as as asphalt and concrete that increases the water that runs off into streams, lakes and rivers.

Shepherd also said that outdated storm water management systems are more easily overwhelmed when these extreme rainfall events occur.


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