Assessment of Tropical Cyclone Risk in Southwestern Western Australia using Multiple Lines of Evidence

Stochastic cyclone models are used to evaulate risk for purposes including placing insurance and reinsurance. These models are highly sensitive to landfall frequency assumptions specially in marginal areas, which tend to be more vulnerable to damage as building code requirements are not as stringent. Considering the study area of southern Western Australia, the long-term tropical cyclone (TC) climatology is compiled and analysed to understand the potential landfall frequency. TCs were identified back to the early 19th century from a range of historical sources such as government survey records, shipping logs, in-situ and remote meteorological observations and newspaper accounts. Their characteristics in terms of location, landfall, intensity, extent, forward speed and raininess were estimated and summarised. TC annual frequencies were then calculated over a range of latitudinal wind regions and temporal eras. The results show that the study area has a long history of TC impacts that may be underappreciated from modern records. The records are dominated by strong interdecadal variability, and no long term trend in frequency was evident. The non- or low cyclonic status of these regions in the building code may be questioned. This extended climatology provide a benchmark for assessment of stochastic TC risk models and climate change trend analysis. Further, it has use cases in emergency management, prioritisation of mitigation investment, and application in building design and land use planning.