A New Historical Tornado Climatology for Australia

A new climatology for the occurrence of tornadoes in Australia is under development for the period 1795 to 2013. Like many countries outside of the United States, the historical records for tornadoes are poorly documented. Existing data from the Australian Bureau of Meteorology National Severe Storms Archive also suffer from observer-driven spatial inhomogeneties, and biases related to institutional policy of event documentation. Recently, extensive library archives of scanned newspapers have become available for Australia that can offer insight into historical events and allow the potential for extension of the existing climatology. Keyword optimization has been used to identify tornadoes from the scanned data while reflecting changes to terms used in the historical vernacular. Additional metadata relating to intensity, time of occurrence, path characteristics, injuries, fatalities and damage is inferred from newspaper accounts. Further, tornadoes from the Severe Storms Archive are cross-validated and additional metadata determined for inclusion in the new climatology.

Based on documentary evidence, tornadoes are rated via the Fujita scale using three categorizations to reflect uncertainty in historical strength determination and more easily identified differences between strength (Weak F0-F1, Strong F2-F3 and Violent F4-F5). The quality of each identified event is categorized into three levels (Possible, Likely or Definite) and is based on the reliability of observations, as well as documentation of characteristics indicating the presence of a tornado event. Preliminary research has shown that the review for the period 1795 to 1900 has increased the existing database by a factor of eight for the same period, and increased its size by two thirds overall. In addition, the historical review has revealed several tornado outbreaks, including an event producing at least 33 tornadoes in a nine-hour period in 1897. These insights into the nature of the historical climatology allow a greater understanding of risks in the present and future relating to deaths from tornadoes, the frequency of outbreaks and violent tornadoes, as well as spatial occurrence. While reviewing historical accounts is painstaking, the climatology has demonstrated the importance of historical climatology for understanding the frequency of severe phenomena such as tornadoes. Going forward, the climatology will be used for the analysis of the synoptic conditions that are favorable to the development of tornadoes in Australia.