On the recent hiatus of tropical cyclones landfalling in NSW, Australia

Abstract

It is well known that severe storms result in some of the costliest natural disasters for New South Wales (NSW), Australia. However, it is not widely acknowledged that some of these events are, in fact, a result of landfalling tropical cyclones (TCs). Indeed, the intense focus of TC research within the tropics generally disregards landfalling TC events in the mid-latitude regions of Australia. This is likely due to the perceived infrequency of these events compared to other more susceptible regions. Therefore, in this study, we review this assumption by developing a 150-year record of TC activity, based on a range of digitised and analogue historical datasets and identify 30 individual landfalling TCs that have impacted NSW. Periods of enhanced and reduced TC activity are observed, with a defined hiatus (absence of landfalling TCs) after approximately 1980. The recent decrease in TC activity is subsequently linked to an increase in El Niño activity and warming of north-west Australian sea-surface temperatures during this time. Importantly, it is possible that a return to enhanced TC activity could occur again in the future if the Pacific conditions align. We also propose that pre-instrumental data on TC activity need to be developed to appropriately quantify TC risk for the study region via the development of local palaeoclimate archives. This study provides a significant contribution to understanding the risks of NSW landfalling TCs and expands upon our knowledge of environmental conditions that influence landfalling TCs in NSW.

Intense east coast lows and associated rainfall in eastern Australia

“…for examining longer-term variations in cyclones and rainfall along eastern Australia. These studies have highlighted large multidecadal variability in the frequency of ECLs and related weather systems, including large numbers of ECL-related floods in the 1860s and 1950s and a decline in floods with tropical influences in recent decades (Power and Callaghan 2016;Gray et al 2020). Large multidecadal variability has also been observed in heavy rainfall events (Ashcroft et al 2019), which some studies have linked to the Interdecadal Pacific Oscillation (Speer 2008).…”

Characterizing Australia's east coast cyclones (1950–2019)

“…This method was then repeated for each seasonal subset. The statistical significance of the cyclone recurrence interval (in months) in the different climate phases (positive, negative and neutral) was evaluated using a test of proportions (Gray et al, 2020; Hogg & Tanis, 1988; Verdon, Kiem, & Franks, 2004). For this test, the total number of ECCs within each phase (e.g.…”

“…positive [y 1 and n 1 ] vs negative ENSO [y 2 and n 2 ]), the combined count was obtained (total number of cyclones in either phase, divided by total number of months in these phases): P 12 = (y 1 + y 2 )/(n 1 + n 2 ). The test statistic was then derived from testing the hypothesis of P 1 = P 2 (Gray et al, 2020; Hogg & Tanis, 1988; Verdon, Kiem, & Franks, 2004). This test was applied for the recurrence intervals over both the total period (from 1950 to 2019) and the seasonal subsets.…”