God forbid, but should another violent twister ravage another American city the way Joplin, Missouri was hit last Sunday, we will remember this as the deadliest tornado season in modern history. At least 505 people have been killed by tornadoes this year, only 14 less than the record 519 who fell victim in 1953. And it's only May. Typically, June is one of the busiest months for tornado activity, and the fall tends to produce some of the strongest storms.
And why has this year been so devastating? While climate change and even rapture prophecies provide tempting rationales, scientists like Bill Gallus, a professor of meteorology at Iowa State University, say the La Niña climate cycle may be responsible; It cools the Gulf of Mexico's water temperature, strengthening storm cells before they sweep over the South.
That answer is somewhat unsatisfying, though. La Niña climate cycles occur every two to seven years, and we haven't seen death tolls like this in more than half a century.
Similarly perplexing, Mr. Gallus' research shows that while reports of tornado activity have risen in past decades, the actual number of "significant tornadoes" of EF-2 strength or greater has stayed the same or even fallen slightly over time. The number of people killed by tornadoes has also declined in recent years to as low as 60 on average.
So the current weather pattern is not so extraordinary, but somehow its destruction absolutely is.
"It seems strange to say, but it's bad luck," Mr. Gallus said. "It's a big coincidence that the tornadoes this year have been hitting fairly large cities."
Sadly, a season like this was bound to occur.
In 2007, four prominent scientists published a study titled "Low-Level Winds in Tornadoes and Potential Catastrophic Tornado Impacts in Urban Areas" in the American Meteorological Society Journal. They wrote that while "fortunately, tornadoes usually spend most or all of their lifetimes over sparsely populated areas ... it is inevitable that someday a large, intense, and long-track tornado will impact a densely populated urban or suburban region." Their research showed that Chicago, New York, Washington DC, St. Louis, Dallas, Houston and Atlanta were particularly vulnerable to damages exceeding one billion dollars in cost, and death tolls in the thousands.
As we saw in Tuscaloosa and Joplin, many homes and businesses in cities throughout America just aren't designed to withstand the winds even of a weak tornado. In the rare year that a strong one tears through these cities, and their poorer neighborhoods in particular, the devastation is incredible.
Mr. Gallus sent one of his students to Tuscaloosa to help with damage surveys. He commented that it was amazing to see how many houses were just sitting on concrete blocks. "They weren't even anchored to the foundation at all."
"Unfortunately, with the outbreak in the Southeast they did all they could, but it still wasn't enough to survive," Mr. Gallus lamented, acknowledging the limits of our sophisticated warning systems. "They hear the safety rules and they think that if I follow the safety rule I'll be OK. But nobody is ever promising that is how it's going to be. You increase your chances of surviving if you follow those rules, but you're still not guaranteed that you're going to survive because things are very wild in a tornado."
One can only hope that we've seen this season's worst. At the same time we should feel fortunate that tornadoes haven't been this destructive in a very long time.