While there is little evidence that tornadoes are increasing in either frequency or intensity, marked jumps in event-reporting and in the number of U.S. mobile home dwellers are among factors explaining recorded-occurrence and damage trends, Lloyd’s says.
A new report published on the Lloyd’s website titled, “Tornadoes: A Rising risk?,” reveals that tornado reports in the United States now average over 1200 per year, citing NOAA counts. Counts of roughly 1000-per-year are indicated for the last two decades on a graph dating back to the 1950s, which also shows that the annual average was more like 650 in the 1960s.
Since the mid-1950s, tornado reports have increased on average by 14 each year, the report says, warning, however that this figure taken alone “means little” and that “socio-economic factors provide a better explanation for this trend than meteorological ones.”
“A large proportion of this can be attributed to population movement to rural areas and increased communication around and understanding of the nature of tornadoes,” the report says.
“The link between increasing population growth and number of reported tornadoes is arguably not entirely coincidental,” noting that fewer U.S. regions remain unpopulated. In addition, “the organization of ‘storm spotter’ networks, community education and awareness programs has increased and improved, making those who might encounter tornadoes in the suburbs and exurbs more weather-aware,” the report says. The Lloyd’s report also notes that advances in technology, such as the Doppler radar, influence increased tornado reporting.
According to the report, the United States experiences more tornadoes than any other nation in the world—owing to a geographical quirk, among other factors. In the United States, an average of 1,200 tornadoes kill at least 60 people, injure 1,500 more and cause over $400 million in economic damage.
The report also cites U.S. Census bureau data revealing a 10-fold jump in U.S. mobile home dwellers between 1950 and 1990, and says that the growing density of mobile home parks in the nation’s “Tornado Alley”—the states of Texas, Oklahoma, Kansas and Nebraska—is placing a greater risk on lives.
Citing National Weather Service figures that date back to the mid-1970s, the report says that 50 percent of U.S. tornado deaths were in mobile homes between 1996 and 2000—nearly double the proportion (24 percent) that occurred between 1976 and 1980. In addition, the report cites a NOAA finding that people living in mobile homes are 23 times more likely to be killed by a tornado than those residing in permanent houses.
The 31-page report also examines worldwide tornado activity, tornado measurement scales, recent U.S. losses and the difficulty in making a link to between climate change and tornado activity.
With respect to climate change, among other difficulties, the report notes the unreliability of long-term tornado records as one factor making it hard to draw a link between extreme weather events that happen on a timescale of seconds and minutes and climate trends that take place over decades.
“While the effects of climate change are not yet clearly observable on tornado activity, it is likely that changing temperatures will affect some of the atmospheric conditions which are favorable to tornado formation,” the report concludes, recommending that possible effects be borne in mind when considering the future of tornado risk.