Using Tornado, Lightning, and Population Data to Identify Tornado Prone Areas in Canada

The first Canadian tornado database was published by Michael Newark of Environment Canada in 1984, and covered the years 1950-1979. A new Canadian tornado database covering the years 1980-2009 has now been developed. Tornado data were assembled from each region of Canada over the 30-year period and refined using a consistent methodology. There are several very large yet relatively remote areas of Canada (e.g. northern Ontario and Quebec, parts of the Prairies) where severe weather is rarely reported, creating significant gaps in the tornado climatology. In order to fill those gaps, and better define ‘tornado-prone' regions of Canada, a combination of tornado, lightning and population data was used. Tornado data from the new 30-yr database, Canadian Lightning Detection Network data from 1999-2008, and population density data from the 2001 census were mapped to a 50 x 50 km grid and tornado occurrence was modelled. Then, using the log-linear relationship for tornado intensity and occurrence that has been noted in the literature, the total tornado occurrence values were partitioned by F-scale value. This resulted in areas defined as being prone to F0-F5 tornadoes and prone to only F0-F1 tornadoes. A third area was added to note where tornadoes occur very rarely. The attached map shows each of these areas, with all tornadoes in the Canadian database going back to 1792 superimposed as a check. The Canadian National Building Code is already making use of this ‘tornado prone' information.