Researchers develop model to correct tornado records

Sep 11, 2013 by Jill Elish

(Phys.org) —In the wake of deadly tornadoes in Oklahoma this past spring, Florida State University researchers have developed a new statistical model that will help determine whether the risk of tornadoes is increasing and whether they are getting stronger.

Climatologists have been hampered in determining actual risks by what they call a population bias: That is, the fact that tornadoes have traditionally been underreported in rural areas compared to cities.

Now, FSU geography Professor James B. Elsner and graduate student Laura E. Michaels have outlined a method that takes the population bias into account, as well as what appears to be a recent surge in the number of reported tornadoes, thanks in part to an increasing number of storm chasers and recreational risk-takers roaming Tornado Alley.

Their model is outlined in the article "The Decreasing Population Bias in Tornado Reports across the Central Plains," published in the American Meteorological Society's journal Weather, Climate, and Society. The model offers a way to correct the historical data to account for the fact that there were fewer reports in previous decades. In addition to Elsner and Michaels, Kelsey N. Scheitlin, an assistant professor at the University of Tennessee at Knoxville, and Ian J. Elsner, a graduate student at the University of Florida, co-authored the paper.

"Most estimates of tornado risk are probably too low because they are based on the reported number of tornadoes," Elsner said. "Our research can help better quantify the actual risk of a tornado. This will help with building codes and emergency awareness. With our research, the science of tornadoes can move forward to address questions related to whether cities enhance or inhibit tornadoes."

Although other researchers have proposed methods to address the population bias, all of them assume the bias is constant over time, Elsner said. This model is the first to take into consideration how the population bias has changed over time.

Historically, the number of reported tornadoes across the premiere storm chase region of the central Plains is lowest in rural areas. However, the number of tornado reports in the countryside has increased dramatically since the 1970s and especially since the 1996 release of the disaster movie "Twister." The movie spawned a generation of storm chasers who are partially responsible for more tornado reports, Elsner said.

Interestingly, Elsner's model was developed after he led a team of undergraduate and graduate students on a storm-chasing mission of their own.

"While we were driving around the Great Plains looking for storms, I challenged my students to think about how the historical data could be used to better estimate the risk of getting hit by a tornado," he said. "The observations of other chasers and the geographic spacing of towns led us to our model for correcting the historical record."

In addition to more storm chasers logging tornado sightings, greater public awareness of tornadoes and advances in reporting technology, including mobile Internet and GPS navigating systems, may also have contributed to the increase in reports over the past 15 to 20 years.

The increase in reports has diminished the population bias somewhat, but it introduced a second problem: There are more reports, but are there also, in fact, more tornadoes? In other words, is the risk actually increasing?

To address these issues, the FSU researchers first made the assumption that the frequency of tornadoes is the same in cities as in rural areas. They also operated on the assumption that the reported number of tornadoes in rural areas is low relative to the actual number of tornadoes.

Their model calls for the reported number in to be adjusted upward by a factor that depends on the number of tornadoes in the nearest city and the distance from the nearest city. The model shows that it is likely that tornadoes are not occurring with greater frequency, but there is some evidence to suggest that tornadoes are, in fact, getting stronger.

"The risk of violent tornadoes appears to be increasing," Elsner said. "The tornadoes in Oklahoma City on May 31 and the 2011 tornadoes in Joplin, Mo., and Tuscaloosa, Ala., suggest that tornadoes may be getting stronger."

The Oklahoma City tornado on May 31, 2013, was the largest tornado ever recorded, with a path of destruction measuring 2.6 miles in width. The Tuscaloosa and Joplin are two of the most deadly and expensive natural disasters in recent U.S. history.

Explore further: New study shows tornadoes tend toward higher elevations and cause greater damage moving uphill

More information: journals.ametsoc.org/doi/abs/10.1175/WCAS-D-12-00040.1?journalCode=wcas

add to favorites email to friend print save as pdf

Related Stories

No rest for the tornado

Jul 30, 2013

(Phys.org) —Do tornadoes take the weekends off? Researchers from NC State University examined the question of the connection between tornado frequency and aerosol pollution, and found that any link between ...

NWS: New tool confirmed Miss. tornado

Feb 16, 2013

(AP)—Officials say new technology allowed forecasters in Mississippi to quickly confirm the tornado that tore through Hattiesburg this week and alert the public.

Explainer: Why are tornadoes so destructive?

May 22, 2013

Tornadoes are a part of life for people living in the Great Plains of the United States. In Oklahoma, a state that averages 62 tornadoes a year, people are prepared as best as they can be and are well warned.

Power of US tornado dwarfs Hiroshima bomb

May 21, 2013

Wind, humidity and rainfall combined precisely to create Monday's massive killer tornado in Oklahoma. The awesome amount of energy released dwarfed the power of the atomic bomb that leveled Hiroshima.

Recommended for you

NASA sees last vestiges of Tropical Depression Jack

15 hours ago

Tropical Cyclone Jack had weakened to a tropical depression when NASA and JAXA's Tropical Rainfall Measuring Mission (TRMM) satellite passed above on April 22, 2014 at 1120 UTC/7:20 a.m. EDT.

New discovery helps solve mystery source of African lava

18 hours ago

Floods of molten lava may sound like the stuff of apocalyptic theorists, but history is littered with evidence of such past events where vast lava outpourings originating deep in the Earth accompany the breakup ...

Climate change likely to make Everest even riskier

19 hours ago

Climbing to the roof of the world is becoming less predictable and possibly more dangerous, scientists say, as climate change brings warmer temperatures that may eat through the ice and snow on Mount Everest.

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

tadchem
not rated yet Sep 11, 2013
The problem with chasing down sources of statistical bias is that each one you uncover and account for, eventually altering your estimates, serves mainly to provide spurious reassurance in the validity of one's model.
Never forget that a model is always a model, and an estimate, no matter how refined, is still just an estimate.
The only way to eliminate statistical biases is to eliminate the need for statistics with a COMPLETE data set. Sometimes, that just cannot be done.

More news stories

On global warming, settled science and George Brandis

The Australian Attorney General, Senator George Brandis is no stranger to controversy. His statement in parliament that "people do have a right to be bigots" rapidly gained him notoriety, and it isn't hard to understand why ...