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

Conventional wisdom holds that improved tornado warnings will reduce tornado casualties, since longer lead time on warnings provides extra opportunity to alert residents who can then take precautions. We provide empirical evidence on the relationship between warnings and casualties using a data set of tornadoes in the contiguous United States between 1986 and 2002. We examine two questions: Does a warning issued on a tornado reduce the resulting number of fatalities and injuries?, and, Do longer lead times reduce casualties? We find 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 minutes reduces fatalities, while longer lead times beyond that point increase fatalities (compared to no warning). The fatalities results, however, are highly sensitive to several killer tornadoes.