A new study shows that tornadoes are changing their behavior pattern to occur in clusters or swarms, increasing the potential for mass destruction.
The study, published in Science by Harold Brooks and other NOAA researchers, showed the increasing number of tornado clusters since the '70s.
"In effect, there is a lower probability of a day having a tornado, but if a day does have a tornado, there is a much higher chance of having many tornadoes. As a result, tornadoes are 'concentrated' into a smaller number of days in more recent years. Approximately 20 percent of the annual tornadoes in the most recent decade have occurred on the three 'biggest' days of each year, in contrast to 10 percent in the earlier period. This concentration leads to the potential for short periods of time, such as months, to have extreme (both large and small) numbers of tornadoes."
While the tornadoes aren't expected to increase in individual occurrences, when tornadoes do strike they are more likely to be devastating in terms of destruction.
"The bottom line is that the risk of big tornado days featuring densely concentrated tornado outbreaks is on the rise," said a similar study from the summer.
Author of the study James Elsner of Florida State University said the tornado swarms could be due to climate change.
"The greater heat and moisture in the atmosphere is a direct result of a warming planet, and the warming is greater at the poles than at lower latitudes, amplifying and slowing the jet stream," which will cause shear that amplifies tornado activity, causing swarms.