Tornado Casualties Research Articles

Revisiting U.S. Nocturnal Tornado Vulnerability and Its Influence on Tornado Impacts

Abstract This research examines tornadoes and their fatalities by light condition (i.e., daytime and nighttime) for the United States. The study has two primary objectives: 1) to catalog and reassess differences in daytime and nighttime, or nocturnal, tornadoes and their fatalities from spatial and temporal perspectives and 2) to employ a spatially explicit Monte Carlo simulation technique to calculate differences in daytime and nocturnal tornado–population impact potential by combining climatological tornado risk data with fine-scale, gridded estimates of day and night population density. Results reveal that nocturnal tornadoes remain a substantial impediment to mitigating tornado casualties despite long-term improvements in detection and warning of these events. Nocturnal tornadoes are nearly 2 times as deadly as daytime events, with fatalities stemming from overnight (i.e., from local midnight to sunrise) tornadoes increasing fourfold since the late nineteenth century. The proportion of all tornado fatalities that occurred during daytime hours has decreased 20% over the last 140 years while the nocturnal fatality proportion has increased 20%. The stall, or even slight growth, in U.S. tornado mortality rates over the last 30 years has, at least in part, been driven by increasing nocturnal tornado fatalities. Overall, nocturnal tornadoes affect 13% more people on average than daytime tornadoes, revealing the importance of time of day in mitigating tornado–population impacts and disasters. Emergency managers, forecasters, first responders, policy makers, and researchers should continue to focus efforts on understanding nocturnal tornadoes, especially with regard to how populations receive warnings and respond to these nocturnal threats.

A place-based analysis of tornado activity and casualties in Shreveport, Louisiana

Tornadoes are among the most violent hazards in the world capable of producing mass casualties. Much of what is known about the relationship between tornadoes and casualties—injuries and fatalities—is driven by quantitative methods that often omit individual community factors. In response, here we present a place-based analysis of tornado activity and casualties in Shreveport, Louisiana. Results show that tornado casualties are more likely in smooth and lower topography and in formally redlined neighborhoods. Results also indicate that areas around the local Barksdale Air Force Base have experienced fewer casualties than other parts of the city since the installation of a Doppler Radar in 1995 and that Shreveport has a greatly reduced casualty rate since the Super Outbreak of 2011. We argue that continued place-based approaches are necessary for an understanding of the multi-dimensional, structural, and historical legacies that produce disproportionate impacts to environmental hazards and that when combined with quantitative methods, place-based approaches have the potential to create regional-or-local intervention strategies that can reduce the loss of life.

Factors associated with injuries among tornado victims in Yancheng and Chifeng, China

BackgroundAs extremely violent meteorological disasters, tornadoes often cause serious casualties. The study aims to analyze the characteristics and causes of tornado injuries in China under certain humanistic and geographical conditions.MethodsA random sampling questionnaire survey was developed and distributed to tornado victims from two separate occurrences: an Enhanced Fujita 4 tornado in Yancheng, and a Fujita 3 tornado in Chifeng. The information of demographic characteristics, disaster environment, and individual behaviors in victims was collected. Chi-square test and binary logistic regression were used to analyze influencing factor of injuries.ResultsA total of 94 valid questionnaires (participation rate 95.9%) were finally collected in Yancheng tornado and 67 valid questionnaires (participation rate 93.1%) in Chifeng tornado. Residents’ annual income (OR = 0.10, 95% CI 0.02–0.50, P = 0.005), degree of house collapse (OR = 183.12, 95% CI 8.04–4173.34, P = 0.001) have a significant impact on the probability of injury. Differences in tornado disaster drill awareness (P = 0.009), individual behaviors (P = 0.011) and fear level (P = 0.011) significantly affected the incidence of trauma. Whether victims were indoors or not has no statistical difference on injuries in China.ConclusionsOur study clarifies risk factors and is conducive to the expansion of the investigation in tornado casualties. The government should improve the wind-resistance of residential buildings. Victims should participate in disaster prevention drills to take effective disaster avoidance actions.

A Model for U.S. Tornado Casualties Involving Interaction between Damage Path Estimates of Population Density and Energy Dissipation

AbstractA recent study showed the importance of tornado energy as a factor in a model for tornado deaths and injuries (casualties). The model was additive under the assumption of uniform threat. Here, we test two explicit hypotheses designed to examine this additive assumption. The first hypothesis concerns energy dissipation’s effect conditional on population density and the second concerns population’s effect conditional on energy. Both hypotheses are tested using a regression model that contains the product of population density and energy dissipation. Results show that the elasticity of casualties with respect to energy dissipation increases with population density. That is, the percentage increase in casualties with increasing energy dissipation increases with population density. Similarly, the elasticity of casualties with respect to population density increases with energy dissipation. That is, the percentage increase in casualties with increasing population density increases with energy dissipation. Allowing energy and population elasticities to be conditional rather than constant provides a more complete description of how tornado casualties are influenced by these two important factors.

Population and energy elasticity of tornado casualties

AbstractTornadoes are capable of catastrophic destruction and mass casualties, but there are yet no estimates of how sensitive the number of casualties are to changes in the number of people in harm's way or to changes in tornado energy. Here the relationship between tornado casualties (deaths and injuries), population, and energy dissipation is quantified using the economic concept of “elasticity.” Records of casualties from individual tornadoes over the period 2007–2015 are fit to a regression model. The coefficient on the population term (population elasticity) indicates that a doubling in population increases the casualty rate by 21% [(17, 24)%, 95% credible interval]. The coefficient on the energy term (energy elasticity) indicates that a doubling in energy dissipation leads to a 33% [(30, 35)%, 95% credible interval] increase in the casualty rate. The difference in elasticity values show that on average, changes in energy dissipation have been relatively more important in explaining tornado casualties than changes in population. Assuming no changes in warning effectiveness or mitigation efforts, these elasticity estimates can be used to project changes in casualties given the known population trends and possible trends in tornado activity.

Preparing for Danger: On the Impact of Tornado Watches on Tornado Casualties

We explore the impact of tornado watches on tornado casualties. The time needed to take shelter for a tornado can be as little as a few minutes, but because warning lead times averaged less than 15 minutes in 2004, a watch could alert residents to be ready to receive and respond to a later warning. We find that casualties per tornado are greater for tornadoes occurring within a tornado watch, although this difference vanishes when controlling for tornado, warning, and path characteristics in a regression analysis. We find no evidence that watches reduce casualties, either directly or by increasing the effectiveness of tornado warnings. Tornadoes occurring within watches are more often warned for and warnings reduce casualties, so watches do contribute to lives saved through the warning process.

Daily Variation in Natural Disaster Casualties: Information Flows, Safety, and Opportunity Costs in Tornado Versus Hurricane Strikes

Casualties from natural disasters may depend on the day of the week they strike. With data from the Spatial Hazard Events and Losses Database for the United States (SHELDUS), daily variation in hurricane and tornado casualties from 5,043 tornado and 2,455 hurricane time/place events is analyzed. Hurricane forecasts provide at-risk populations with considerable lead time. Such lead time allows strategic behavior in choosing protective measures under hurricane threat; opportunity costs in terms of lost income are higher during weekdays than during weekends. On the other hand, the lead time provided by tornadoes is near zero; hence tornados generate no opportunity costs. Tornado casualties are related to risk information flows, which are higher during workdays than during leisure periods, and are related to sheltering-in-place opportunities, which are better in permanent buildings like businesses and schools. Consistent with theoretical expectations, random effects negative binomial regression results indicate that tornado events occurring on the workdays of Monday through Thursday are significantly less lethal than tornados that occur on weekends. In direct contrast, and also consistent with theory, the expected count of hurricane casualties increases significantly with weekday occurrences. The policy implications of observed daily variation in tornado and hurricane events are considered.

False Alarms, Tornado Warnings, and Tornado Casualties

AbstractThis paper extends prior research on the societal value of tornado warnings to the impact of false alarms. Intuition and theory suggest that false alarms will reduce the response to warnings, yet little evidence of a “false alarm effect” has been unearthed. This paper exploits differences in the false-alarm ratio across the United States to test for a false-alarm effect in a regression model of tornado casualties from 1986 to 2004. A statistically significant and large false-alarm effect is found: tornadoes that occur in an area with a higher false-alarm ratio kill and injure more people, everything else being constant. The effect is consistent across false-alarm ratios defined over different geographies and time intervals. A one-standard-deviation increase in the false-alarm ratio increases expected fatalities by between 12% and 29% and increases expected injuries by between 14% and 32%. The reduction in the national tornado false-alarm ratio over the period reduced fatalities by 4%–11% and injuries by 4%–13%. The casualty effects of false alarms and warning lead times are approximately equal in magnitude, suggesting that the National Weather Service could not reduce casualties by trading off a higher probability of detection for a higher false-alarm ratio, or vice versa.

Tornado Warnings, Lead Times, and Tornado Casualties: An Empirical Investigation

AbstractConventional wisdom holds that improved tornado warnings will reduce tornado casualties, because longer lead times on warnings provide extra opportunities to alert residents who can then take precautions. The relationship between warnings and casualties is examined using a dataset of tornadoes in the contiguous United States between 1986 and 2002. Two questions are examined: Does a warning issued on a tornado reduce the resulting number of fatalities and injuries? Do longer lead times reduce casualties? It is found that warnings have had a significant and consistent effect on tornado injuries, with a reduction of over 40% at some lead time intervals. The results for fatalities are mixed. An increase in lead time up to about 15 min reduces fatalities, while lead times longer than 15 min increase fatalities compared with no warning. The fatality results beyond 15 min, however, depend on five killer tornadoes and consequently are not robust.

Improvements in Tornado Warnings and Tornado Casualties

Doppler radar installation by the National Weather Service (NWS) improved tornado warning performance, raising the probability of detection and mean lead time while reducing the false alarm ratio. Research on tornado casualties has established that a warning reduces tornado injuries while lead times of up to fifteen minutes also reduce tornado fatalities. In this paper we estimate the decrease in tornado casualties attributable to the observed change in the distribution of warning lead times, and thus provide evidence on the benefit to society of weather warning systems. We find that increases in warning lead times accounts for 30–50 percent of the reduction in injuries but no more than 1/4 of the reduction in fatalities which occurred with the installation of Doppler radar by the NWS. Future improvements in warning performance to further reduce tornado fatalities by 18 percent and injuries by 24 percent.

WSR-88D Radar, Tornado Warnings, and Tornado Casualties

Abstract The impact of the installation of Weather Surveillance Radar-1988 Doppler (WSR-88D) radars in the 1990s on the quality of tornado warnings and occurrence of tornado casualties is examined. This analysis employs a dataset of tornadoes in the contiguous United States between 1986 and 1999. The date of WSR-88D radar installation in each National Weather Service Weather Forecast Office is used to divide the sample. Tornado warnings improved after the installation of Doppler radar; the percentage of tornadoes warned for increased from 35% before WSR-88D installation to 60% after installation while the mean lead time on warnings increased from 5.3 to 9.5 min and the false alarm ratio fell slightly. A regression analysis of tornado casualties, which controls for the characteristics of a tornado and its path, reveals that expected fatalities and expected injuries were 45% and 40% lower for tornadoes occurring after WSR-88D radar was installed in the NWS Weather Forecast Office. This analysis also finds that expected casualties are significantly lower for tornadoes occurring during the day or evening than late at night throughout the sample, which provides indirect evidence of the life-saving effects of tornado warnings.

Protection from Nature’s Fury: Analysis of Fatalities and Injuries from F5 Tornadoes

Improved technology and warnings seem to have reduced tornado casualties over time. We subject this conventional wisdom to empirical scrutiny by examining the determinants over time of casualties from the strongest (F5) tornadoes in the United States since 1900. We limit analysis to F5 tornadoes to control for the strength of storms and then control for economic and demographic characteristics of the storm paths in a regression analysis of casualties. We find significant negative time trends over the periods 1900 to 1999 when controlling for population density and 1950 to 1999 when also controlling for income. Our results indicate that everything else being equal, fatalities from an F5 tornado were 40% lower in 1999 than 1950 and 90% lower in 1999 than 1900.

The Determinants of Tornado Casualties and the Benefits of Tornado Shelters

Several recent powerful tornadoes have raised interest among the public and policymakers in tornado shelters. We estimate casualty functions (fatalities, injuries) based on factors like storm intensity, county population density, and time of day, using historical data from Oklahoma and then estimate expected tornado casualties for Oklahoma using historical tornado frequencies assuming no further market penetration of shelters. We then calculate the cost per life saved and injury prevented for shelters. The cost per life saved for shelters in permanent homes without discounting is around $30 million. Shelters will then provide cost effective protection for residents of mobile homes.