Australian Tornadoes: Climatology 1795-2014 Compared to a ‘Record' 2013

A new climatology for the occurrence of tornadoes in Australia has been developed for the period 1795 to 2014, the second largest single country record. However, extensive media coverage in 2013 raised the question ‘Was 2013 a record tornado year?' Like many places 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 limitations, and biases related to institutional policy of event documentation. Recently, extensive library archives of scanned newspapers, and digitization of the original severe thunderstorm reports material have become available for Australia that can offer insight into historical events and extend the existing climatology.

Keyword optimization was 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 were inferred from newspaper accounts. Further, tornadoes from the existing Severe Storms Archive were cross-validated and additional metadata determined for inclusion in the new climatology. Based on documentary evidence, tornadoes were rated via the Fujita scale using three categorizations to reflect uncertainty in historical strength determination (Weak F0-F1, Strong F2-F3 and Violent F4-F5). The quality of record for each identified event was categorized into three levels (Possible, Likely or Definite) based on the reliability of observations, as well as documentation of characteristics indicating the presence of a tornadic event.

The climatology in context of a recent observed year (2013) will be presented, highlighting that the annual frequency of tornadoes in Australia ranges between 30 and 80 observed tornado events per year but likely underestimates the total frequency given underreporting due to population density. Numerous tornado outbreak cases have also been identified throughout the length of the record. To further illustrate the risk posed for Australia by tornadoes, cases from 2013 encompassing the broad spectrum of tornado formative environments will be discussed. These results reveal that Australia is subject to tornadoes from most environmental sources on a relatively frequent basis, and this should play a greater role in the forecasting and warning process.