NWC REU 2011
May 23 - July 29



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Deriving Population Exposure Fatality Rate Estimates for Tornado Outbreaks Using Geographic Information Systems (GIS)

Amber R. Cannon, Kim Klockow, Randy Peppler, and Harold Brooks


What is already known:

  • The tornado outbreak in April of 2011 caused a high number of fatalities.
  • Effectiveness of current tornado warning procedures was called into question.
  • Are present-day tornadic outbreaks stronger or more deadly than historical outbreaks?

What this study adds:

  • Rubrics for 1) outbreak population and fatality rate analysis and 2) the fatality rate for a single event provide a basis for comparison between two or more events.
  • Tornado warning effectiveness in Alabama has improved from 1974 to 2011 based on these outbreaks.
  • County level population appears reasonable for comparing historical and present day outbreaks.
  • GIS can be used to innovatively evaluate tornado warning effectiveness.


In this study we looked at several issues regarding the derivation of population exposure and fatality rate estimates during widespread tornado outbreaks. The two events studied were the April 3, 1974 and April 27, 2011 tornado outbreaks in the state of Alabama. We attempted to determine if tornado warnings have become more effective over time at reducing the number of fatalities. We used GIS to perform an analysis on these outbreaks. We found that the effectiveness of tornado warnings did improve between the two outbreaks, and we can have reasonably high confidence in using county level population data to compare recent and historical outbreaks, although the higher resolution of the census track data is preferred for studying a single tornadic event. We also found that the accuracy of fatality rates is directly related to the accuracy of the path data. Finally, GIS can be used to innovatively evaluate tornado warning effectiveness.

Full Paper [PDF]