Spatial Redistribution of U.S. Tornado Activity between 1954 and 2013

Abstract

limate change over the past several decades prompted this preliminary investigation into the possible effects of global warming on the climatological behavior of U.S. tornadoes for the domain bounded by 30°?50°N and 80°?105°W. On the basis of a warming trend over the past 30 years, the modern tornado record can be divided into a cold ?Period I? from 1954 to 1983 and a subsequent 30-year warm ?Period II? from 1984 to 2013. Tornado counts and days for (E)F1?(E)F5, significant, and the most violent tornadoes across a 2.5° ? 2.5° gridded domain indicate a general decrease in tornado activity from Period I to Period II concentrated in Texas/Oklahoma and increases concentrated in Tennessee/Alabama. These changes show a new geographical distribution of tornado activity for Period II when compared with Period I. Statistical analysis that is based on field significance testing and the bootstrapping method provides proof for the observed decrease in annual tornado activity in the traditional ?Tornado Alley? and the emergence of a new maximum center of tornado activity. Seasonal analyses of both counts and days for tornadoes and significant tornadoes show similar results in the spring, summer, and winter seasons, with a substantial decrease in the central plains during summer. The autumn season displays substantial increases in both tornado counts and significant-tornado counts in the region stretching from Mississippi into Indiana. Similar results are found from the seasonal analysis of both tornado days and significant-tornado days. This temporal change of spatial patterns in tornado activity for successive cold and warm periods may be suggestive of climate change effects yet warrants the climatological study of meteorological parameters responsible for tornado formation.