Spatiotemporal Analysis of Near-Miss Violent Tornadoes in the United States

Abstract

In the hazards literature, a near-miss is defined as an event that had a nontrivial probability of causing loss of life or property but did not due to chance. Frequent near-misses can desensitize the public to tornado risk and reduce responses to warnings. Violent tornadoes rarely hit densely populated areas, but when they do they can cause substantial loss of life. It is unknown how frequently violent tornadoes narrowly miss a populated area. To address this question, this study looks at the spatial distribution of possible exposures of people to violent tornadoes in the United States. We collected and replicated tornado footprints for all reported U.S. violent tornadoes between 1995 and 2016, across a uniform circular grid, with a radius of 40 km and a resolution of 0.5 km, surrounding the centroid of the original footprint. We then estimated the number of people exposed to each tornado footprint using proportional allocation. We found that violent tornadoes tended to touch down in less populated areas with only 33.1% potentially impacting 5000 persons or more. Hits and near-misses were most common in the Southern Plains and Southeast United States with the highest risk in central Oklahoma and northern Alabama. Knowledge about the location of frequent near-misses can help emergency managers and risk communicators target communities that might be more vulnerable, due to an underestimation of tornado risk, for educational campaigns. By increasing educational efforts in these high-risk areas, it might be possible to improve local knowledge and reduce casualties when violent tornadoes do hit.

A tornado daily impacts simulator for the central and southern United States

“…To show how the TorDIS can be used to study spatial variations in tornado impacts, the 1,000 year annual simulation was subset to focus on six metropolitan statistical areas (MSAs): Oklahoma City (Oklahoma), Dallas/Fort Worth (Texas), Chicago (Illinois), Birmingham (Alabama), Omaha (Nebraska) and St. Louis (Missouri), hereafter references to the city name refer to the MSA. These MSAs were chosen for their size (from < 1 million persons in Omaha to > 9 million persons in Chicago; US Census Bureau, ), distribution throughout the model domain and varying levels of tornado hazards (tornado hazards are most common in an “L”‐shaped pattern between Nebraska, Texas and Alabama, and they drop off further towards the northeast; Concannon et al ., ; Ashley, ; Hatzis et al ., ).…”

“…The annual impacts are greater in Birmingham at lower thresholds due to the higher rural density (Ashley, ), while the annual impacts are greater in Omaha at slightly higher thresholds because most of the population in Omaha is confined to the centre (US Census Bureau, ). This implies that tornadoes are unlikely to impact many people, but when they do, the totals will be higher (Hatzis et al ., ). In fact, despite being the least populous MSA in the present study, significant tornadoes impacting Omaha nearly had the same probability of impacting 20,000 persons as in Oklahoma City, which had nearly 400,000 more people in 2010 (Table ).…”

“…However, since the objective is to assess the long-term risk of tornado impacts and not the impacts for a specific year, this methodology was considered to be acceptable. This mode can be used to assess the longterm risk of population exposures exceeding 5,000 persons in a given area (Hatzis et al, 2019). The objective in both modes is to determine the statistical distribution of potential tornado impacts over the period from which the atmospheric environmental data are drawn (i.e.…”

“…To show how the TorDIS can be used to study spatial variations in tornado impacts, the 1,000 year annual simulation was subset to focus on six metropolitan statistical areas (MSAs): Oklahoma City (Oklahoma), Dallas/Fort Worth (Texas), Chicago (Illinois), Birmingham (Alabama), Omaha (Nebraska) and St. Louis (Missouri), hereafter references to the city name refer to the MSA. These MSAs were chosen for their size (from < 1 million persons in Omaha to > 9 million persons in Chicago; US Census Bureau, 2010), distribution throughout the model domain and varying levels of tornado hazards (tornado hazards are most common in an "L"-shaped pattern F I G U R E 5 Monthly variation in median significant tornado counts (a) and median annual persons exposed to significant tornado winds (b) over the study area for a 1,000 year simulation T A B L E 2 Impact analysis from a 1,000 year Tornado Daily Impacts Simulator (TorDIS) simulation over the study area between Nebraska, Texas and Alabama, and they drop off further towards the northeast; Concannon et al, 2000;Ashley, 2007;Hatzis et al, 2019). The normalized significant tornado count was highest over Birmingham (112) and lowest over St. Louis (82) ( Table 3).…”

“…For the high-impact tornadoes, the probability that the exposure of a simulated violent tornado would be higher than observed, on the date of the event, was 1.5%, 3.6% and 2.7% for Tuscaloosa-Birmingham, Joplin and Moore, respectively. Given that all three tornadoes impacted > 5,000 persons, it is not surprising that these exposures are not very likely to be exceeded (Hatzis et al, 2019).…”