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Dec 20, 2022
Can we attribute the intense precipitation event in the Brisbane region in February 2022 to climate change?
Camille Cadiou, Robin Noyelle, Nemo Malhomme & Davide Faranda
Can we attribute the intense precipitation event in the Brisbane region in February 2022 to climate change?

Cumulated precipitations between the 23rd of February and 3rd of March 2022 in south-east Australia according to the NCEP reanalysis.

Can we attribute the intense precipitation event in the Brisbane region in February 2022 to climate change?

Camille Cadiou, Robin Noyelle, Nemo Malhomme & Davide Faranda
 
From the last week of February to mid-March 2022, the eastern coast of Australia faced an episode of intense rainfall. 345mm of rain was recorded at Brisbane on the 28th of February. The intense rain occurred while soils were already close to saturation from the recent precipitations in the end of 2021. This led to severe and enduring floodings during the month of March. The intense precipitations were caused by a combination of ingredients: tropical moisture was first deflected to the subtropics, then collected and lifted by a low pressure system stationed over Eastern Australia blocked by a high pressure offshore the Coral sea. This combination created an atmospheric river capable of transporting several gigaliters of water towards Queensland and the South West of the continent.


This extreme precipitation event was unprecedented in the Brisbane region and very intense with respect to previous historical records in the broader Eastern coast of Australia. To understand to what extent climate change could have influenced this extreme event, researchers employed attribution methods, which aims to quantify the influence of climate change on a meteorological event and to investigate the physical mechanisms that lead to it.


In this paper, the ESTIMR team used two attribution methods: a classical one based on return time statistics and a new one introduced recently by the team and based on the atmospheric circulation. The first method consists in comparing the likelihood of observing an event so intense in the past with respect to the present. If this probability is greater in the present climate, it means climate change made this event more likely.  The second one compares the large air masses and the high and low pressure systems at the time of the rain bomb event. Then it determines if a similar situation had already occurred in the recent (1990-2020) and remote past (1950-1980). The systematic comparison between the recent and remote past allows them to compare the impacts of a similar atmospheric configuration when the influence of climate change on the atmosphere was still weak. 


The climate of Australia is strongly influenced by the natural evolution of the climate, in particular a large atmospheric and oceanic oscillation called El-Niño-Southern-Oscillation (ENSO). ENSO is a phenomenon of the Pacific region that irregularly alternates between two phases. During the event, ENSO was in the La Niña phase, which induces additional air moisture in the south West Pacific and wind circulation patterns that could have played a role in the intensity of the event. They adapt the attribution methods to compare between El Niño and La Niña phases and evaluate how ENSO could have played a role in the intensity of the event.


The statistical attribution shows that this event has a low probability of happening both in the past and present climates (less than one in a century). This first attribution method yields no clear signal of a climate change influence. The second method reaches similar conclusions, with no clear signal of climate change on precipitation for the atmospheric configuration observed. It is likely that the La Niña phase of the ENSO played a significant role in the intensity of the event.


These results are coherent with what the IPCC report states about rainfall over Australia, namely that “Available evidence has not shown an increase or a decrease in heavy precipitation over Australasia as a whole (medium confidence), but heavy precipitation tends to increase over Northern Australia (particularly the north-west) and decrease over the eastern and southern regions.” 

Reference

Cadiou*, C., Noyelle*, R., Malhomme, N., Faranda D.  Challenges in Attributing the 2022 Australian Rain Bomb to Climate Change. Asia-Pac J Atmos Sci (2022). https://doi.org/10.1007/s13143-022-00305-1

*Equal Contributions

Acknowledgments

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement N 956396 under grant agreement No. 101003469 (XAIDA).

 
 
#326 - Last update : 12/20 2022
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