Comparative Analysis of the Tornado Outbreaks Of April 3-4, 1974 and April 27-28, 2011: Deriving Population Exposure Fatality Rate Estimates for Tornado Outbreaks Using Geographic Information Systems (GIS)

This study derived and compared population exposure and fatality rate estimates from two widespread tornado outbreaks using a GIS. The two events included the April 3, 1974 and April 27, 2011 tornado outbreaks, and comparisons were made at the state level (examining Alabama in particular) and then the outbreak level. This research asks specifically whether tornado warnings have become more effective over time at reducing the number of fatalities. We present an analysis of population data at various scales to demonstrate the robustness of our estimation approach, and show that county level population data can be used to compare recent and historical outbreaks, although the higher resolution of the census track data is preferred for studying a single tornadic event. Also, dynamic modeling could be used to achieve further accuracy by incorporating time sensitive population data. An increase in tornado warning effectiveness could not be determined based on this analysis because the data failed to demonstrate a significant difference in fatality rates. This suggests that for tornadoes of a given intensity and size, warning advancements that continue to promote the current shelter-in-place paradigm may not reduce fatality rates. It was also discovered that the accuracy of population exposure and resulting fatality rates is directly related to the accuracy of the tornado path data at the tract level but not necessarily at the county level. Finally, a GIS can be used to innovatively evaluate population exposure and fatality rates as well as compare the characteristics of two or more tornado outbreaks.