Population and energy elasticity of tornado casualties

Abstract

Tornadoes 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.

Increasingly Powerful Tornadoes in the United States

“…Tornado power is metered by the energy dissipated near the ground (Fricker et al, 2017). On average, the longest lasting tornadoes generate the most extreme wind speeds (Brooks, 2004;Elsner, Jagger, & Elsner, 2014;Fricker & Elsner, 2015).…”

“…We calculate tornado power (P) using the energy dissipation equation defined in Fricker et al (2017) as…”

“…Here we focus on the available recent period of this record from 1994 to 2016. Additional details and justification for using tornado power are given in Fricker et al (2017). The fraction of path area is that recommended by the U.S. Nuclear Regulatory Commission (Fricker & Elsner, 2015), which combines a Rankine vortex with empirical estimates derived from detailed storm surveys (Ramsdell & Rishel, 2007).…”

“…On days with 16 to 31 tornadoes less than 4% of the tornadoes are rated EF3 or worse while on days with more than 63 tornadoes more than 8% of the tornadoes are rated EF3 or worse (Table 1). of casualties when people are present (Fricker et al, 2017). This leads us to hypothesize that tornadoes are becoming more powerful.…”

Spatial Distributions of Tropical Cyclone Tornadoes by Intensity and Size Characteristics

“…The greatest casualty count is 32, which is related to one of TC Bonnie's (2004) F 2 tornadoes with a path length of 8 km, path width of 457 m, and DPI of 4.26. This tornado intersected multiple residential areas, which illustrates that tornado-related losses are a function of the size and intensity of a tornado along with the impacted socioeconomic landscape [26,27].…”