The massive rainfall that caused a devastating flash flood in Ellicott City, Md., last weekend was a rare 1-in-1,000-year event that has been happening with unprecedented frequency in recent years, meteorologists said.
The storm, which killed two people, 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.
A 1-in-1,000-year rain event is a statistical way of expressing the probability of such a massive rainfall occurring in any given year in a given location, according to the National Center for Environmental Information, which is part of the National Oceanic and Atmospheric Administration. In other words, it had a 1 in 1,000 chance of occurring in Ellicott City in any year.
This is at least the ninth “1-in-1,000” year rain event across the United States since 2010, and the third this year. Flooding in Houston in April killed eight people. And in June, 23 died in a in West Virginia flood caused by heavy rain.
So many “1-in-1,000 year” rainfalls appear unprecedented. “The number of these type of events has seemingly become more pronounced in recent years,” meteorologist Steve Bowen of a global reinsurance firm Aon Benfield said in a tweet Monday.
Source: Rain that caused deadly Maryland flood was another ‘1-in-1,000’ year event