Natural Hazards: Tornadoes
KeywordsNatural hazard Protective actions Protective behavior Risk communication
A tornado is a rotating wind funnel generated by very large thunderstorms called supercell. In case the wind changes direction, there is an opportunity for moist and cold air to combine forming a rotating funnel.
Tornadoes can occur everywhere. In the United States, every year there are more than one thousand tornadoes (Haddow et al. 2014). In term of seasonality, tornadoes occur more frequently from March to August and primarily during the afternoon and evening “between noon and midnight” (Haddow et al. 2014, p. 44). In the United States, tornadoes occur more frequently in an area called “tornado alley” than in other regions. Tornado alley is an area covering several states such as Texas, Oklahoma, and Kansas. However, the number of tornadoes now occurring in the southeast, such as in Mississippi, Alabama, Arkansas, Missouri, and Illinois, is becoming frequent (Berardelli, December 16, 2018). The main consequences in this shift in tornado location are that damage is worse due to the dense population and number of trees in these areas that prevent people from spotting them on the ground. In addition, there are more frame houses in this region than in Oklahoma for instance, meaning that the homes are vulnerable (Berardelli, December 16, 2018). Important aspects of tornadoes management involve damage measurement, risk communication (such as how do we warn the population about potential or actual risk), protective measures (e.g., actions people are required to undertake on the basis of their location), and people’s behavior in responding to this threat. The following sections will discuss these points.
Tornado Damage Measurement and Wind Speed Estimates
Enhanced Fujita scale
Peels surface off some roofs; some damage to gutters or siding; branches broken off trees; shallow-rooted trees pushed over
Roofs severely stripped; mobile homes overturned or badly damaged; loss of exterior doors, windows, and other glass broken
Roofs torn off well-constructed houses; foundations of frame homes shifted; mobile homes completely destroyed; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground
Entire stories of well-constructed houses destroyed; severe damage to large buildings such as shopping malls; trains overturned; trees debarked; heavy cars lifted off the ground and thrown; structures with weak foundations blown away some distance
Well-constructed houses and whole frame houses completely leveled; cars thrown; and small missiles generated
Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air in excess of 100 m (109 yd); high-rise buildings have significant structural deformation; incredible phenomena will occur
The deadliest tornado in the United States was the March 18, 1925, Tri-state tornado which encompassed the states of Missouri, Illinois, and Indiana. This tornado killed 695 people, of which 613 in the sole state of Illinois. The widest tornado ever recorded in the United States is the EF 5 El Reno tornado recorded on May 31, 2013, in Oklahoma with a 2.6-miles (4.2 km) width (The National Weather Service). To have an idea of the width of the tornado, it is useful to remember that 2.6 miles is the actual length of central park in New York City (Climate Central, May 4th 2013). The El Reno tornado showed the importance of taking into account possibilities rather than probabilities. Even though EF5 tornadoes are the most severe tornadoes, what really makes a difference are the mitigation activities, the preparedness, and response of the affected communities.
Risk Communication, Tornado Watch, Tornado Warnings, and Tornado Emergency
In the United States, the National Weather Service (NWS) is the public agency responsible for issuing severe weather forecasts to the public. To this aim, the agency designed the Severe Weather Watch/Warning System. The purpose of the severe weather watch/warning system is to alert the public to hazardous weather situations and encourage them to take actions to enhance protection of life and property, despite recognizing that the final decision falls on individuals and households (Black and Ashley 2011). In order to fulfill its mission, the NWS defines both tornado watch and warning on the basis of the level of threat posed to people and to the action to be undertaken for each case (Pifer and Mogil 1978). The watches and warning are used for a variety of hazards such as floods, hurricanes, and thunderstorm and are considered as the cornerstone of severe weather risk communication. Tornado watch means that the “conditions are favorable for the development of tornadoes in and close to the watch area. During the watch, people should review tornado safety rules and be prepared to move a place of safety if threatening weather approaches” (NWS, Glossary). Tornado warning is issued by the National Weather Service when “a tornado is indicated by the WSR-88D radar or sighted by spotters” (NWS, Glossary). Under special circumstances, the NWS also issues Tornado emergencies.
A tornado emergency is a step-up to tornado warning and it is issued for all those situations that are extremely life-threatening in highly populated areas. The reason for which tornado emergency is issued in addition to tornado warning is that some communities might be accustomed and therefore complacent to tornado warnings. The first tornado emergency was issued on May 3, 1999, during the Bridge Creek EF5 outbreak and the last to date was issued during the Lee County, Alabama, March 3rd tornado, where 23 people lost their lives. Since the first tornado emergency, a total of 129 tornado emergency have been issued.
Another way to warn population of an incoming tornado threat is through the use of sirens. However, this is not always the best way. For instance, in Hodler’s (1982) study of public response to the Kalamazoo Tornado, 17% of respondents did not understand the meaning of the warning siren that was sounded in order to warn citizens of potential danger, despite the fact that the sirens were tested every month. Other factors impacting people’s understanding of warnings includes the amount of information conveyed through a message (DiGiovanni et al. 2002), the amount of time spent living in a specific area (Haas et al. 1977; Foster 1980; Perry and Greene 1983; Perry and Lindell 1986; Blanchard-Boehm 1998), and sociodemographic characteristics. For instance, the content of the warning can be misunderstood because of cultural or language barriers (Aguirre 1988), or because of the use of technical terms such as the use of probability to refer to the occurrence of a tornado (Morss et al. 2010) and some scholars have even suggested that terms such as watch and warning may contribute to a lack of understanding (Powell and O’Hair 2008; Donner et al. 2007).
The protective actions to be undertaken by people in the affected area in case of a tornado warning depend on one’s location. If at home or in a business, the safest place to be according to Federal Emergency Management Agency (FEMA) are safe rooms and ICC 500 storm shelters, if either of these have been installed. Safe rooms and ICC 500 storm shelters are particularly recommended for those areas often affected by tornadoes such as those located in a “tornado alley.” In absence of a safe room or ICC 500 storm shelters, the most interior windowless room located at the lower level of the house, such as a closet or a bathroom or a basement, are preferred. It is important in all of these situations to get additional protection through the use of mattresses and blankets which serve to cover residents in order to mitigate the effects of flying debris. If in a car, the best thing to do pull off the road and try to reach safe shelters; if this is not possible, the next best option is to lie in a ditch face down with one’s head covered by both hands.
However, the choice of which protective action to undertake can also be confusing for the population under warning in case of overlapping hazards. For instance, during the 2017 Hurricane Harvey in Texas, the NWS issued several overlapping tornado warning and flash flood warnings. The protective actions in case of flash flood warning (i.e., get to higher ground) are the opposite to those in case of a tornado warning, the latter of which required people at home to go to the lower level (Evans 2018).
In conclusion, tornadoes are a complex natural hazard which varies in intensity and therefore in loss of lives and properties. While, in the United States, there are some areas such as the tornado alley that are more tornado prone than others, even less prone states or states which usually are affected by less intense tornadoes should be ready to prepare for, heed the warning, and undertake protective actions. Particular attention should be posed at the understanding of warning terms such as tornado watch and tornado warning in conjunction with the potential existence of disaster subcultures.
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