Why Australia was not wet during spring 2020 despite La Niña

Abstract The austral spring climate of 2020 was characterised by the occurrence of La Niña, which is the most predictable climate driver of Australian springtime rainfall. Consistent with this La Niña, the Bureau of Meteorology’s dynamical sub-seasonal to seasonal forecast system, ACCESS-S1, made hi...

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Autores principales:	Eun-Pa Lim, Debra Hudson, Matthew C. Wheeler, Andrew G. Marshall, Andrew King, Hongyan Zhu, Harry H. Hendon, Catherine de Burgh-Day, Blair Trewin, Morwenna Griffiths, Avijeet Ramchurn, Griffith Young
Formato:	article
Lenguaje:	EN
Publicado:	Nature Portfolio 2021
Materias:	Medicine R Science Q
Acceso en línea:	https://doaj.org/article/251baed10f6c409ead12b8c44a2ea06a
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spelling	oai:doaj.org-article:251baed10f6c409ead12b8c44a2ea06a2021-12-02T18:50:03ZWhy Australia was not wet during spring 2020 despite La Niña10.1038/s41598-021-97690-w2045-2322https://doaj.org/article/251baed10f6c409ead12b8c44a2ea06a2021-09-01T00:00:00Zhttps://doi.org/10.1038/s41598-021-97690-whttps://doaj.org/toc/2045-2322Abstract The austral spring climate of 2020 was characterised by the occurrence of La Niña, which is the most predictable climate driver of Australian springtime rainfall. Consistent with this La Niña, the Bureau of Meteorology’s dynamical sub-seasonal to seasonal forecast system, ACCESS-S1, made highly confident predictions of wetter-than-normal conditions over central and eastern Australia for spring when initialised in July 2020 and thereafter. However, many areas of Australia received near average to severely below average rainfall, particularly during November. Possible causes of the deviation of rainfall from its historical response to La Niña and causes of the forecast error are explored with observational and reanalysis data for the period 1979–2020 and real-time forecasts of ACCESS-S1 initialised in July to November 2020. Several compounding factors were identified as key contributors to the drier-than-anticipated spring conditions. Although the ocean surface to the north of Australia was warmer than normal, which would have acted to promote rainfall over northern Australia, it was not as warm as expected from its historical relationship with La Niña and its long-term warming trend. Moreover, a negative phase of the Indian Ocean Dipole mode, which typically acts to increase spring rainfall in southern Australia, decayed earlier than normal in October. Finally, the Madden–Julian Oscillation activity over the equatorial Indian Ocean acted to suppress rainfall across northern and eastern Australia during November. While ACCESS-S1 accurately predicted the strength of La Niña over the Niño3.4 region, it over-predicted the ocean warming to the north of Australia and under-predicted the strength of the November MJO event, leading to an over-prediction of the Australian spring rainfall and especially the November-mean rainfall.Eun-Pa LimDebra HudsonMatthew C. WheelerAndrew G. MarshallAndrew KingHongyan ZhuHarry H. HendonCatherine de Burgh-DayBlair TrewinMorwenna GriffithsAvijeet RamchurnGriffith YoungNature PortfolioarticleMedicineRScienceQENScientific Reports, Vol 11, Iss 1, Pp 1-15 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Medicine R Science Q
spellingShingle	Medicine R Science Q Eun-Pa Lim Debra Hudson Matthew C. Wheeler Andrew G. Marshall Andrew King Hongyan Zhu Harry H. Hendon Catherine de Burgh-Day Blair Trewin Morwenna Griffiths Avijeet Ramchurn Griffith Young Why Australia was not wet during spring 2020 despite La Niña
description	Abstract The austral spring climate of 2020 was characterised by the occurrence of La Niña, which is the most predictable climate driver of Australian springtime rainfall. Consistent with this La Niña, the Bureau of Meteorology’s dynamical sub-seasonal to seasonal forecast system, ACCESS-S1, made highly confident predictions of wetter-than-normal conditions over central and eastern Australia for spring when initialised in July 2020 and thereafter. However, many areas of Australia received near average to severely below average rainfall, particularly during November. Possible causes of the deviation of rainfall from its historical response to La Niña and causes of the forecast error are explored with observational and reanalysis data for the period 1979–2020 and real-time forecasts of ACCESS-S1 initialised in July to November 2020. Several compounding factors were identified as key contributors to the drier-than-anticipated spring conditions. Although the ocean surface to the north of Australia was warmer than normal, which would have acted to promote rainfall over northern Australia, it was not as warm as expected from its historical relationship with La Niña and its long-term warming trend. Moreover, a negative phase of the Indian Ocean Dipole mode, which typically acts to increase spring rainfall in southern Australia, decayed earlier than normal in October. Finally, the Madden–Julian Oscillation activity over the equatorial Indian Ocean acted to suppress rainfall across northern and eastern Australia during November. While ACCESS-S1 accurately predicted the strength of La Niña over the Niño3.4 region, it over-predicted the ocean warming to the north of Australia and under-predicted the strength of the November MJO event, leading to an over-prediction of the Australian spring rainfall and especially the November-mean rainfall.
format	article
author	Eun-Pa Lim Debra Hudson Matthew C. Wheeler Andrew G. Marshall Andrew King Hongyan Zhu Harry H. Hendon Catherine de Burgh-Day Blair Trewin Morwenna Griffiths Avijeet Ramchurn Griffith Young
author_facet	Eun-Pa Lim Debra Hudson Matthew C. Wheeler Andrew G. Marshall Andrew King Hongyan Zhu Harry H. Hendon Catherine de Burgh-Day Blair Trewin Morwenna Griffiths Avijeet Ramchurn Griffith Young
author_sort	Eun-Pa Lim
title	Why Australia was not wet during spring 2020 despite La Niña
title_short	Why Australia was not wet during spring 2020 despite La Niña
title_full	Why Australia was not wet during spring 2020 despite La Niña
title_fullStr	Why Australia was not wet during spring 2020 despite La Niña
title_full_unstemmed	Why Australia was not wet during spring 2020 despite La Niña
title_sort	why australia was not wet during spring 2020 despite la niña
publisher	Nature Portfolio
publishDate	2021
url	https://doaj.org/article/251baed10f6c409ead12b8c44a2ea06a
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Why Australia was not wet during spring 2020 despite La Niña

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