Study: Number Of Multi-tornado Days Is Increasing
October 17, 2014
By The Daily Oklahoman
When an EF4 tornado tore through Shawnee and Bethel Acres last year, it was one of eight such storms that touched down in Oklahoma that day.
Nationwide, multi-tornado days like the one Oklahoma saw on May 19, 2013, appear to be increasing, according to a new National Oceanographic and Atmospheric Administration study.
Although the average number of tornadoes per year in the United States has remained relatively constant over the past six decades, the nation is seeing fewer days per year on which tornadoes occur, the report suggests. That means on days when tornadoes do occur, there are more likely to be several tornadoes instead of just one.
That trend could lead to greater likelihood of larger-scale catastrophes and put extra strain on emergency responders, a researcher said.
The study, which appears this week in the journal "Science," was conducted by a team of climate scientists from the National Severe Storms Laboratory and the National Weather Service`s Storm Prediction Center in Norman.
During the study, researchers set out to shed light on whether a relationship exists between climate change and the number of tornadoes that occur in the United States on average each year. Researchers analyzed records from NOAA`s database of tornadoes of all but the weakest tornadoes that occurred between 1954 and 2013.
When they compared records of recent tornado occurrences with those from decades ago, researchers noticed a gradual decline in the average number of days per year on which a tornado occurs somewhere in the country. In the 1970s, records showed about 150 days per year where a tornado rated F1 or greater occurred. By 2010, that average had dropped to about 100 days per year.
During the same period, researchers noticed an increase in the number of days per year when several tornadoes occurred. In the 1970s, the country saw about one day every other year in which 30 or more tornadoes occurred. By 2010, the country averaged about three such days each year.
"The number of days with a lot of tornadoes are going up," said Harold Brooks, senior research scientist at the National Severe Storms Laboratory.
Brooks, the paper`s lead author, said more research needs to be done before scientists can determine why tornadoes seem to be concentrated on fewer days per year. The study`s findings don`t point to a specific cause, but Brooks said the shift may be the result of shifts in atmospheric and weather patterns associated with climate change.
"It could well be," he said.
If the number of multi-tornado days continues to rise, it could place additional burdens on disaster responders, Brooks said.
When several tornadoes struck Oklahoma on May 19-20, 2013, emergency resources were spread out in several areas across the state. Brooks said situations like those could create a range of concerns, including having enough medical personnel to treat the injured and finding enough equipment to repair cities` power infrastructures when they`re knocked out.
"If you start having more outbreaks, then you start having to worry about using all those resources," he said.
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(c)2014 The Oklahoman
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Story image: Speedwell resident Tommy Ellison looks for family papers in the rubble of his home Monday, July 28, 2014, near LaFollette, Tenn. The National Weather Service confirmed a F-3 tornado packing winds of 140 mph slammed into the Speedwell community, leveling 10 homes and a business. AP Photo/Knoxville News Sentinel, J. Miles Cary
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