Spatial and Temporal Characteristics of the Population Bias in U.S. Tornado Reports
The official tornado report record is limited by a significant bias. Termed the "population bias", it communicates misleading climatological trend information by displaying an increasing number of reports from 1950 through the early 2000s. This increase in reports is most likely due to inc...
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| Format: | Others |
| Language: | English English |
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Florida State University
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| Online Access: | http://purl.flvc.org/fsu/fd/FSU_migr_etd-7510 |
| Summary: | The official tornado report record is limited by a significant bias. Termed the "population bias", it communicates misleading climatological trend information by displaying an increasing number of reports from 1950 through the early 2000s. This increase in reports is most likely due to increasing technology and awareness regarding tornadoes. This led to more reports being made and less being missed, as opposed to an increase of tornado events. We propose a method for quantifying this population bias in four regions, the Central Plains, Northern Plains, Southeast, and Midwest using bounding boxes spanning multiple states in each region. A spatial model is developed, which calculates the distance from the nearest city on a 128 X 128 grid within each region. The city locations are based on the 1990 census. The tornado report density is also computed at each grid point, and we explore the relationship between report density and distance from the nearest city. We then use that relationship to quantify the population bias as the ratio of the maximum report density to minimum report density in the vicinity of a city. We find that this population bias has a general decrease throughout the record, and the most significant decrease is after the induction of radar in the early 1990s. The bias has diminished for all regions within the most recent years of the record. We find that the changing nature of this population bias has a regional dependency, which must be addressed when considering a model with a population bias term in future studies. We also speculate that we are now reporting all tornadoes in all regions. === A Thesis submitted to the Department of Geography in partial fulfillment of the requirements for the degree of Master of Science. === Summer Semester, 2013. === June 28, 2013. === geography, population bias, spatial model, tornado === Includes bibliographical references. === James Elsner, Professor Directing Thesis; Jay Baker, Committee Member; Chris Uejio, Committee Member. |
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