A severe winter storm record for southwestern Australia, 1830–2024

Abstract This study describes the development of the longest sub-daily pressure record available from Australia and the Southern Hemisphere. We present newly consolidated mean sea level pressure observations for Perth in southwestern Australia, spanning 1830–2024. After establishing the quality of the new sub-daily pressure record, we evaluate its ability to resolve severe storms, verifying them against the synoptic fields generated by the 20th Century Reanalysis and independent historical records. We calculate a severe storm index for Perth using extreme pressure changes to assess any long-term changes in austral winter (June–August) storm activity back to 1830. Our results show a 20.2% decrease in the number of winter storms influencing Perth since 1970, with the decline further strengthening to 30.9% since 1990. The most recent decade (2010–2019) shows the lowest number of storms compared with any other decade since 1830. A supporting analysis of Perth rain days since 1830 displays considerable inter-annual variability and a notable reduction in winter rainfall since the 1970s. These results provide further evidence of a drying trend across southern Australia previously attributed to anthropogenically-influenced shifts in westerly storm tracks and changes in storm characteristics. We also identify a protracted dry period between 1830–1846 that is more pronounced than the current rainfall deficit. This analysis suggests that twentieth and twenty-first century weather observations do not capture the range of natural variability and extremes recorded in pre-industrial records, implying that future weather and climate risk is likely to be underestimated in the Australian region.