Applying historical records to extend the tropical cyclone climatology in southwestern Australia, 1830–2023

Historical climatologies of tropical cyclones have been constructed for five of the Earth's seven tropical cyclone basins and this reappraisal for the southeastern Indian Ocean moves a step closer to completing a global compilation for the 19th and 20th centuries. The need for longer-term climatologies is especially pronounced in our case-study region in the southwest area of Western Australia, where TC Alby (1978) is unique as an example of an unpredictable, high-impact event in the era of modern satellite monitoring. We identify 29 events for a ~ 130-year period preceding 1960. Based on this extended record, tropical cyclone frequencies are calculated over a range of timeframes and latitudinal ranges. The record is dominated by strong interdecadal variability, and no long-term trend in frequency was determined. While no severe (Australian Category 3 and above) tropical cyclones have made landfall in Perth or adjacent regional cities over the past ~200 years, our results clearly show that southwestern Australia has a long history of tropical cyclone impacts, calling into question its classification within the Australian building code as a non-cyclonic region. This revised climatology provides a basis for development of and comparison with stochastic tropical cyclone hazard models and climate change trend analysis, with use cases across emergency management, prioritisation of mitigation investment, re/insurance risk pricing, wind and storm surge hazard assessment, and associated uses in building design and land use planning. These findings underline the value of historical records for understanding tropical cyclones in areas of marginal cyclone influence and/or where instrumental observations are available for only the past 50–60 years.