A new study shows the number of deadly tornado outbreaks in the U.S. has been increasing.
For the study, researchers looked at figures from the National Oceanic and Atmospheric Administration from 1954 to 2014 to discover a four-fold increase in the chances of tornado cluster outbreaks, according to CBS News. The study also revealed an increase in the number of tornadoes involved in each cluster.
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Tornado clusters are series of twisters that can span for several days. For the study, researchers tracked instances where six or more EF-1 tornadoes formed within six hours of each other. EF-1 tornadoes typically have winds between 86 and 110 mph.
The clusters are considered the most dangerous type of tornadoes, as they account for 79 percent of tornado deaths.
Although the number of severe tornadoes hasn’t changed significantly since the 1950s, the average number of tornadoes per outbreak increased, as did the swings between high and low numbers of twisters, which raises the chance of extreme outbreaks.
In one horrific case, a three-day tornado cluster in 2011 involved 350 tornadoes and killed more than 300 people in the south-central United States.
“These discoveries suggest that the risks from tornado outbreaks are rising far faster than previously recognized,” Joel Cohen, who coauthored the study, said.
Cohen, a mathematical population biologist, conducted the study with Climate Researcher Michael Tippett. The study was published in the Nature Communications journal Feb. 29.
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The results are similar to other studies that have measured the frequency of tornado clusters.
The researchers cautioned that blaming climate change for the increased clusters is “premature” and emphasized that additional research is needed.
