INFORMACIÓN GENERAL DE LOS MARCOS SELECCIONADOS

While deaths and injuries associated with tornadoes is a well-researched field, much less has been done to evaluate the relationship between economic losses and tornado events. This thesis presents an analysis of tornadoes from 1990-2012, specifically focusing on the property and crop losses sustained during these tornado events. Since the National Weather Service switched from the Fujita scale rating system to the Enhanced Fujita scale in 2007, the first part of this research analyzed the

comparability between the two scales. The second part looked at the geographic location of tornadoes over time, specifically looking at the movement of tornado clusters as determined by the Getis-Ord Gi* statistic. The final part of this thesis analyzed extreme tornadoes and extreme losses, mapping them geographically and determining the statistical relationship between the two variables.

The implementation of the Enhanced Fujita scale in 2007 brought with it the question of its comparability with the previously used Fujita scale. This research has shown that the two scales are comparable when the tornadoes are rated 3, 4, or 5; however, the scales are not equal when looking at tornadoes rated 0, 1, or 2.

Specifically, there has been an increase in the number of tornadoes rated 1 and 2 on the Enhanced Fujita scale, and a decrease in the number of tornadoes rated 0. This verifies previous research done comparing the early years of the two scales. The change in

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rating between the two scales can be explained (at least in part) by the way tornadoes are rated on the new scale, which includes twenty-seven more indicators of tornado damage than did the original Fujita scale. Since fewer tornadoes are rated as EF0 on the new scale, it brings into question whether some tornadoes rated F0 on the Fujita scale may in fact be underrepresenting the tornado’s true intensity. As this research has shown that the Fujita and Enhanced Fujita scales are not the same for lower-rated tornadoes, they should not be treated as such in future research.

Tornadoes are most commonly known for their presence in the areas known as Tornado and Dixie Alleys. The answer to the second research question has shown that high numbers of tornadoes do in fact occur in Tornado Alley and Dixie Alley.

Additionally, there is an area of high tornado occurrence in the southern portion of the Florida peninsula. An analysis of yearly mean tornado cluster location showed that tornadoes have moved northward and eastward over time. However, this analysis also introduced the possibility that while tornadoes moved eastward from 1990 to the early 2000s, tornadoes have since moved back westward. If this trend continues in the future, areas in northern Tornado Alley and northern Dixie Alley may see more tornadoes than they have in the past. On a more localized scale, communities which reside to the north of where tornadoes occur now may need to make adjustments to their emergency plans to include an increased tornado threat in the future. This research has not been able to clearly determine the movement of tornadoes longitudinally over time, and it is unclear whether tornado clusters will move eastward or westward in the future. Additional

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research over a longer study period is needed to determine the future east-west movement of tornadoes.

Research Question 3 showed that areas in the United States characterized by tornadoes with extreme damages and extreme tornadoes include central Tornado Alley, eastern Dixie Alley, and along the Kentucky/Illinois/Indiana border. However, this

research has also demonstrated that extreme tornadoes are not always the same tornadoes as those incurring extreme losses. There are parts of the country, particularly in Iowa, Illinois, Missouri, North Carolina, and South Carolina, where tornadoes create a large amount of economic loss but are not defined as extreme tornadoes based on their Enhanced Fujita scale rating. In these areas, non-extreme tornadoes can produce

extreme damages. With the increase in the amount of things people own as population and wealth increases in the future, the number of non-extreme tornadoes causing extreme damage could potentially increase.

The fourth research question evaluated the relationship between extreme tornadoes and extreme losses and found that F/EF5 tornadoes have a greater mean, range, and standard deviation than F/EF4 tornadoes, but that the distribution was less skewed. Since an increase in tornado rating from 4 to 5 indicates structures having had greater damage, the increase in average economic loss is not surprising. This research question also looked at the different methods of declaring a tornado as extreme. As shown previously, extreme tornadoes are not the only tornadoes that produce extreme damage. This research has shown that the list of tornadoes rated F/EF4 and F/EF5 is not the same as the list of tornadoes producing more than $1 million in damages using the

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CPI method of inflation, and that neither of these lists is the same as the list of tornadoes producing more than $1 million in damages using inflation by county GDP. This confirms the earlier statement that producing extreme economic loss is not the same as a tornado being rated extreme on the Enhanced Fujita scale.

Studying economic losses incurred during tornado events is important to developing a comprehensive assessment of tornado hazards. The first step,

understanding how economic loss and extreme tornadoes are related, has been started here. A few questions arise from the results of this research: 1) Why has the location of tornadoes over time changed, and is that trend likely to continue in the future? 2) How will the movement of tornadoes over time affect the locations of extreme tornadoes and tornadoes with extreme losses? 3) How could the Enhanced Fujita scale be improved to take into account the non-extreme tornadoes that produce extreme economic loss? Future research aiming to address these questions would help increase scientists’ understanding of tornado events, and could provide communities with better ways to mitigate tornado events of the future. With the uncertainty of how climate change will affect tornado intensity and location, the answers to these questions will become more important as communities prepare for a changing tornado climate.

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Appendix A: Tornado Rating and Counts Boxplots

65 Figure A.2: Boxplots for F/EF1 Tornadoes

66 Figure A.3: Boxplots for F/EF2 Tornadoes

67 Figure A.4: Boxplots for F/EF3 Tornadoes

68 Figure A.5: Boxplots for F/EF4 Tornadoes

69 Figure A.6: Boxplots for F/EF5 Tornadoes