Preprints
https://doi.org/10.5194/egusphere-2024-3149
https://doi.org/10.5194/egusphere-2024-3149
28 Nov 2024
 | 28 Nov 2024
Status: this preprint is open for discussion.

Interdecadal Cycles in Australian Annual Rainfall

Tobias F. Selkirk, Andrew W. Western, and J. Angus Webb

Abstract. The extremes of Australian rainfall have profound economic, ecological and societal impacts; however, the current forecast horizon is limited to a few months. This study investigates interdecadal periodicity in annual rainfall records across eastern Australia. Wavelet analysis was conducted on rainfall data from 347 sites covering 130 years (1890–2020). Prominent cycles were extracted from each site and clustered using a Gaussian Mixture Model. This revealed three principal cycles centred around 12.9, 20.4 and 29.1 years that were highly significant over red noise by t-test (p<0.0001). Overall, the three cycles combined had a mean contribution to total rainfall variance (R2) of 13 % across all sites, but this was up to 29 % at individual sites. Both the 12.9-yr and 20.4-yr cycles were detected at over 95 % of sites. The strength of each cycle varied over time and this amplitude modulation of the signal showed a systematic movement across the area investigated. 86 % of extremely wet years fell within the positive phase of the combined reconstruction, with 80 % of extremely dry years falling in the negative phase. These results indicate underlying periodicity in annual rainfall across eastern Australia, with the potential to build this into long-term forecasts. This concept has been suggested in the past, but not rigorously tested. These findings open new paths for research into rainfall patterns in Australia and internationally. They also have broad implications for the management of water resources across all sectors.

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Tobias F. Selkirk, Andrew W. Western, and J. Angus Webb

Status: open (until 14 Jan 2025)

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  • RC1: 'Comment on egusphere-2024-3149', Anonymous Referee #1, 08 Dec 2024 reply
Tobias F. Selkirk, Andrew W. Western, and J. Angus Webb
Tobias F. Selkirk, Andrew W. Western, and J. Angus Webb

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Short summary
This study investigated rainfall in eastern Australia to search for patterns that may aid in predicting flood and drought. The current popular consensus is that such cycles do not exist. We analysed 130 years of rainfall using a very modern technique for identifying cycles in complex signals. The results showed strong evidence for three clear cycles of 12.9, 20.4 and 29.1 years with a confidence of 99.99 %. When combined, they showed an 80 % alignment to years of extremely high and low rainfall.