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A Statistical Model for Regional Tornado Climate Studies.

Jagger TH, Elsner JB, Widen HM - PLoS ONE (2015)

Bottom Line: The model is significantly improved by adding terrain roughness.The effect amounts to an 18% reduction in the number of tornadoes for every ten meter increase in elevation standard deviation.Flexibility of the model is illustrated by fitting it to data from Illinois, Mississippi, South Dakota, and Ohio.

View Article: PubMed Central - PubMed

Affiliation: Department of Geography, Florida State University, Tallahassee, Florida, United States of America.

ABSTRACT
Tornado reports are locally rare, often clustered, and of variable quality making it difficult to use them directly to describe regional tornado climatology. Here a statistical model is demonstrated that overcomes some of these difficulties and produces a smoothed regional-scale climatology of tornado occurrences. The model is applied to data aggregated at the level of counties. These data include annual population, annual tornado counts and an index of terrain roughness. The model has a term to capture the smoothed frequency relative to the state average. The model is used to examine whether terrain roughness is related to tornado frequency and whether there are differences in tornado activity by County Warning Area (CWA). A key finding is that tornado reports increase by 13% for a two-fold increase in population across Kansas after accounting for improvements in rating procedures. Independent of this relationship, tornadoes have been increasing at an annual rate of 1.9%. Another finding is the pattern of correlated residuals showing more Kansas tornadoes in a corridor of counties running roughly north to south across the west central part of the state consistent with the dryline climatology. The model is significantly improved by adding terrain roughness. The effect amounts to an 18% reduction in the number of tornadoes for every ten meter increase in elevation standard deviation. The model indicates that tornadoes are 51% more likely to occur in counties served by the CWAs of DDC and GID than elsewhere in the state. Flexibility of the model is illustrated by fitting it to data from Illinois, Mississippi, South Dakota, and Ohio.

No MeSH data available.


Related in: MedlinePlus

Tornado report frequency by county for Kansas.Only tornadoes rated EF1 and higher are used. Lines show the tornado track. The shortest tracks are not visible at this scale. Total tornado counts over the period 1970–2013 are listed inside the county and the color scale is from few (blue) to many (red).
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pone.0131876.g004: Tornado report frequency by county for Kansas.Only tornadoes rated EF1 and higher are used. Lines show the tornado track. The shortest tracks are not visible at this scale. Total tornado counts over the period 1970–2013 are listed inside the county and the color scale is from few (blue) to many (red).

Mentions: The result is a space-time data set with constant-time attributes that include county area and terrain roughness, and variable-time attributes that include the annual number of tornadoes and population density. Area is converted to units of square kilometers and the tornado rate per county is computed as the number of tornadoes per 10,000 square kilometers per year. Tornadoes are most numerous across central Kansas (Fig 4). The larger counties tend to have more tornado reports although the relationship is not large [r = .34 (.19, .48) 90% CI] since the counties tend to have similar sizes. Regional hot spots include Sedgwick County (city of Wichita) and parts of the northeast in the counties around Kansas City. The correlation between the 2012 county population and the number of tornadoes is not significant [r = .04 (−.12, .20) 90% CI]. The annual number of tornado reports for the state as a whole has increased since 1970 at a rate of less than one per year, but the trend is not significant (Fig 5). Summary statistics are listed in Table 1.


A Statistical Model for Regional Tornado Climate Studies.

Jagger TH, Elsner JB, Widen HM - PLoS ONE (2015)

Tornado report frequency by county for Kansas.Only tornadoes rated EF1 and higher are used. Lines show the tornado track. The shortest tracks are not visible at this scale. Total tornado counts over the period 1970–2013 are listed inside the county and the color scale is from few (blue) to many (red).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4526675&req=5

pone.0131876.g004: Tornado report frequency by county for Kansas.Only tornadoes rated EF1 and higher are used. Lines show the tornado track. The shortest tracks are not visible at this scale. Total tornado counts over the period 1970–2013 are listed inside the county and the color scale is from few (blue) to many (red).
Mentions: The result is a space-time data set with constant-time attributes that include county area and terrain roughness, and variable-time attributes that include the annual number of tornadoes and population density. Area is converted to units of square kilometers and the tornado rate per county is computed as the number of tornadoes per 10,000 square kilometers per year. Tornadoes are most numerous across central Kansas (Fig 4). The larger counties tend to have more tornado reports although the relationship is not large [r = .34 (.19, .48) 90% CI] since the counties tend to have similar sizes. Regional hot spots include Sedgwick County (city of Wichita) and parts of the northeast in the counties around Kansas City. The correlation between the 2012 county population and the number of tornadoes is not significant [r = .04 (−.12, .20) 90% CI]. The annual number of tornado reports for the state as a whole has increased since 1970 at a rate of less than one per year, but the trend is not significant (Fig 5). Summary statistics are listed in Table 1.

Bottom Line: The model is significantly improved by adding terrain roughness.The effect amounts to an 18% reduction in the number of tornadoes for every ten meter increase in elevation standard deviation.Flexibility of the model is illustrated by fitting it to data from Illinois, Mississippi, South Dakota, and Ohio.

View Article: PubMed Central - PubMed

Affiliation: Department of Geography, Florida State University, Tallahassee, Florida, United States of America.

ABSTRACT
Tornado reports are locally rare, often clustered, and of variable quality making it difficult to use them directly to describe regional tornado climatology. Here a statistical model is demonstrated that overcomes some of these difficulties and produces a smoothed regional-scale climatology of tornado occurrences. The model is applied to data aggregated at the level of counties. These data include annual population, annual tornado counts and an index of terrain roughness. The model has a term to capture the smoothed frequency relative to the state average. The model is used to examine whether terrain roughness is related to tornado frequency and whether there are differences in tornado activity by County Warning Area (CWA). A key finding is that tornado reports increase by 13% for a two-fold increase in population across Kansas after accounting for improvements in rating procedures. Independent of this relationship, tornadoes have been increasing at an annual rate of 1.9%. Another finding is the pattern of correlated residuals showing more Kansas tornadoes in a corridor of counties running roughly north to south across the west central part of the state consistent with the dryline climatology. The model is significantly improved by adding terrain roughness. The effect amounts to an 18% reduction in the number of tornadoes for every ten meter increase in elevation standard deviation. The model indicates that tornadoes are 51% more likely to occur in counties served by the CWAs of DDC and GID than elsewhere in the state. Flexibility of the model is illustrated by fitting it to data from Illinois, Mississippi, South Dakota, and Ohio.

No MeSH data available.


Related in: MedlinePlus