No Trends in Tornadoes


Average annual number of tornadoes reported by state; the darker the color, the more twisters. (Click for larger map)

There is a somewhat ridiculous premise underlying American football that nobody talks about. After the ball carrier is tackled, the game’s officials make a rough estimate of where the player fell. The offensive team then starts another play from that spot. It continues like this, play after play, until the referees believe the offense has progressed 10 yards. If uncertainty exists, officials bring out a 10-yard measuring stick that can determine where the ball is within a fraction of an inch. Essentially, they take a precise measurement on guesswork and consider it gospel.

There is an analogous situation in the world of tornado tracking. Even in the United States — by far the world’s most frequent victim of twisters — detailed records only go back to 1950. Since then, there has been an average increase of 14 reported tornadoes per year. But any attempt to tie the rise to the weather would be an exercise in analyzing guesswork. Most experts believe this rise is due to advances in science, technology and observational techniques — not to mention the number of homes and businesses that are hit — rather than any objective trend that proves more tornadoes are occurring.

Really, nobody knows — now or then — how many tornadoes occur each year. “Socio-economic factors provide a better explanation for this trend than meteorological ones,” states a report by Lloyd’s of London.

Those who lost loved ones during 2011, a record-setting year for twisters, are unlikely to take solace in this fact. But “despite the anomalous 2011 season,” says the Lloyd’s report, “there is no trend in the number of strong to violent tornadoes between 1950 and 2012.”

The study does note, however, that an objective increase is irrelevant when it comes to the insurance industry’s exposure to the risk. One of the main reasons there are more reports of tornadoes is simply because more homes and businesses are in their path. More people are there to become victims.

“Although the number of violent tornado losses may not be increasing, insured losses are,” states the report. “There is a clear trend of increasing annual aggregate losses to the insurance market, and billion dollar losses are becoming more common.”

Worse still for the industry, there may be a further increase due to rising temperatures. Then again, like judging a first down, that is more guesswork than anything. The increase is measurable, but those doing the counting aren’t exactly seeing the field accurately.

Jared Wade

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About the Author

Jared Wade is a freelance writer and the former senior editor of Risk Management.


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