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New study shows an increase in Tornadoes in the Midwest and Deep South

A study in Nature Partner Journals (NPJ) of Climate and Atmospheric science shows a shift in where tornadoes are happening and possibly likely to happen in the future. 

The paper Spatial Trends in United States Tornado Frequency says. 

National annual frequencies of tornado reports have remained relatively constant, but significant spatially-varying temporal trends in tornado frequency have occurred since 1979

Meaning the number of tornadoes annually has not changed, but where they are happening has observably changed. The study was conducted to look at possible severe weather impacts due to climate change. It looked at tornado reports and a proxy, Significant Tornado Parameter (STP) that measures tornadic environment, from 1979 to 2017.

The paper makes a good argument that tornado reports and STP can be used to predict a changing trend in tornado frequency and location over long term climate trends.

Both variables show a decrease in occurrences in the central plains and an increase in occurrences in Midwest ( including Indiana) and “Dixie Alley” in the south.

Theil-Sen slope analysis of 1979–2017 annual gridded tornado reports. p values are hatched at values ≤ 0.05 significance using Kendall’s τ statistic. Slope units are reports per year * 10−1 NPJ

Areas in red show an increase, blue a decrease on both plots. 

Theil-Sen slope analysis of 1979–2017 annual grid-point sum of daily max STP from NARR. p values are hatched at values ≤ 0.05 significance using Kendall’s τ statistic. Slope units are sum of daily max STP per year NPJ

No major conclusions were made but the paper stresses the importance to monitor the trend. 

“At this point, it is unclear whether the observed trends in tornado environment and report frequency are due to natural variability or being altered by anthropogenic forcing on the climate system.”

The study also notes limitations, one being a data set only possible since the late 70s, the modern weather satellite data era.

If this trend is proven with further study it would confirm a increasing tornado risk for more populated areas of the country and could be linked to climate change as conditions for tornadoes grows as the climate warms. 

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