Over the past few decades, tornadoes have been shifting — decreasing in Oklahoma, Texas and Kansas but spinning up more in Illinois and other states along the Mississippi River and farther east, a new study shows.
Though scientists aren’t sure why, tornado activity is increasing most in Illinois, Indiana, Wisconsin, Mississippi, Arkansas, Tennessee, Louisiana, Alabama, Kentucky, Missouri, Iowa and parts of Ohio and Michigan, according to a study published in the journal Climate and Atmospheric Science.
There has been a slight decrease in the Great Plains, with the biggest drop in central and eastern Texas. Even with the decline, Texas — which likes to boast that everything is bigger there — still gets more tornadoes than any other state.
The shift could be deadly because the area with increasing tornado activity is bigger and home to more people, says Victor Gensini, a professor of atmospheric sciences at Northern Illinois University, the study’s lead author.
Also, more people live in vulnerable mobile homes and tornadoes are more likely to happen at night in those places, Gensini says.
Even though Texas, Kansas and Oklahoma get many more tornadoes, the four deadliest states for tornadoes are Alabama, Missouri, Tennessee and Arkansas, according to the National Oceanic and Atmospheric Administration.
“More folks are generally at risk because of that eastward shift,” Gensini says.
Because tornadoes sometimes go undercounted, especially in less populous areas, scientists don’t like to study trends by using counts of tornadoes.
Gensini and tornado scientist Harold Brooks of the National Severe Storms Lab looked at “significant tornado parameters,” a measurement of the key ingredients of tornado conditions. It looks at differences between wind speed and direction at different altitudes, how unstable the air is and humidity. The more of those three ingredients, the more likely tornadoes will form.
The increases in this measurement mirrored slightly smaller increases found in number of twisters.
The study looked at changes since 1979. Everywhere east of the Mississippi, except the west coast of Florida, is seeing some increase in tornado activity. The biggest increase occurred in states bordering the Mississippi River.
Overall, there’s a slight increase in tornado activity, but it’s not too much and not nearly like what’s happening in the east, according to Gensini.
Why? “We don’t know,” Gensini says. “This is super-consistent with climate change.”
As the Great Plains dry out, there’s less moisture to have the type of storms that spawn tornadoes, Gensini says. Tornadoes form along the “dry line” where there are more thunderstorms because there’s dry air to the west and moist air from the Gulf of Mexico to the east.
That dry line is moving east.
“This is what you would expect in a climate-change scenario,” Gensini says. “We just have no way of confirming it at the moment.”
He says that unless specific, detailed studies are done, he and others can’t say this is caused by global warming — just that it looks like what’s expected with global warming.
Pennsylvania State University meteorology professor Paul Markowski, who wasn’t part of the research, praised the study as careful and well done.