The Danger Zone? The Effect of Storm-based Tornado Warnings on Expected Casualties
Bilder, Michael T.
For decades, the National Weather Service (NWS) issued tornado warnings on a county-level. As a result, an entire county would be warned, even if only a small portion of the population was in danger. Over-warning for tornado threats can lead to a very dangerous sense of complacency amongst the public. On October 1, 2007, the agency converted to issuing storm-based warnings, through which meteorologists would design a unique warning area (shaped as a polygon) that projects the general path they expect a tornado or potentially tornadic storm cell to take. In theory, this approach limits the warning audience to the part of a county that could be directly impacted by a tornado. Narrowing the warning should reduce the impact of false alarms, as well as enable individuals to better assess the risk of harm and the value of taking shelter, thereby reducing the number of expected tornado casualties. Using regression analysis, this thesis tests to see if the way in which the NWS uses geography to communicate proximity to tornado risk has an effect on expected casualties. The effect of reducing the warning area size is controlled for by incorporating into the model the average county area reduction score for each county tornado event. This variable failed to achieve significance. Consequently, the thesis cannot conclude that the switch to storm-based warnings has had a statistically significant effect on reducing or increasing expected casualties. The lack of significance could be attributed to insufficient data, although the dataset contains nearly all county tornado events since the policy took effect. An alternative explanation is that most of the current warning dissemination systems are incapable of only alerting individuals located within the unique boundaries of the polygon.
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