So far, the U.S. tornado season is getting off to a rip-roaring start, with more than 1,051 tornadoes reported, at least 444 of those confirmed. It could break the previous records for tornado seasons if this trend continues, although there have been some spectacular early tornado seasons in the past that later fizzled and ended up being average or below average years.
But the good news is that these numbers don’t yet approach the deadliest tornadoes in U.S. history, including more than 700 killed and 2,027 injured by the Tri-State Tornado of March 18, 1925, which carved a path of destruction for hundreds of miles from Missouri to Indiana.
Today, there may be numerous dangerous tornadoes in a given year, but a higher percentage of people survive because of warnings and shelters and better building construction — even though our population growth is putting more people in harm’s way.
Are tornadoes becoming more frequent than ever before? Here, the evidence is inconclusive. Data from the National Oceanographic and Atmospheric Administration seem to show a fairly stable but fluctuating trend of about 800 to 1,000 tornadoes per year between 1970 and 1988. Then, starting in 1989, the trend climbs to about 1,200 tornadoes per year, with a big spike of 1,300 to 1,400 tornadoes in 1998 and 2003, 1,692 in 2008, 1,156 in 2009, and 1,282 in 2010.
As far as I know, no one has done a careful statistical analysis to see if this trend is meaningful and whether it holds up against the records over the past century.
But it would not surprise me to find that the warming of the tropics that drives hurricanes also means more energy in those Gulf Coast warm moist air masses that cause tornadoes.
Donald R. Prothero, the author of “Catastrophes: Earthquakes, Tsunamis, Tornadoes, and Other Earth-Shattering Disasters,” is a professor of geology at Occidental College in Los Angeles.