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Tornadoes and Drought

This past weekend, tornadoes battered a number of states around the country, killing over 40 people in 15 states, including 24 in North Carolina. Experts believe the weekend could be one of the worst three-day tornado outbreaks in the country's history.  Unfortunately, tornadoes are difficult to study: though clues are available in local atmospheric data, tornadoes are so spontaneous that tracking and taking measurements from them is problematic. (In fact, last year the National Oceanic and Atmospheric Administration (NOAA) and the National Science Foundation (NSF) wrapped up the field portion of the "largest tornado research project in history," with the impossibly cool name of VORTEX2.) Like any extreme weather event, though, scientists want to know the answer to a longer-term question: will climate change affect the frequency of tornadoes?

Scientists are only starting to look for direct connections between the two, but a study by scientists at Purdue and the University of Georgia suggests tornadoes could actually become less frequent. The authors compiled data on the number of "tornado days" and "multiple tornado days" from March to June between 1952 and 2007, as well as cumulative rainfall data for the six months (September-February) leading up to that period. They found that "non-drought years had nearly twice as many tornado days in the study area as drought years and were also five to six times more likely to have multiple tornado days." Since the UN's Intergovernmental Panel on Climate Change expects climate change to increase the frequency and intensity of droughts, the authors indicate that tornadoes could decrease in frequency and severity. On the downside, that could also mean fewer VORTEX projects, and the world needs all the cool project names it can get.