Climate models

Climate models indicate potential for La Niña rain


THE likelihood of above-average precipitation in northern and eastern Australia during the summer has increased, with the Bureau of Meteorology today declaring that a La Niña has developed in the Pacific Ocean .

The office said La Niña is part of a cycle known as El Niño-Southern Oscillation (ENSO), a natural change in ocean temperatures and weather conditions along the equator in the Pacific Ocean.

During La Niña, the waters of the central or eastern tropical Pacific become cooler than normal, persistent southeast to northwest winds strengthen in the tropical and equatorial Pacific, and clouds move westward , closer to Australia, the office said.

The office’s head of operational climate services, Dr Andrew Watkins, said that typically during La Niña events, precipitation is concentrated in the western tropical Pacific, resulting in a wetter than normal period for the eastern, northern and central parts. from Australia.

“La Niña also increases the risk of cooler-than-average daytime temperatures for much of Australia and may increase the number of tropical cyclones that form.

“La Niña is also associated with the earlier first rains of the northern rainy season, as we have seen across much of tropical Australia this year,” Dr Watkins said.

“The last significant La Niña took place in 2010-12.

“This strong event had significant impacts across Australia, including the wettest two-year spells on record in Australia and widespread flooding,” he said.

“La Niña also occurred in the spring and summer of 2020-21. Back-to-back La Niña events are not unusual, with around half of all past events returning for a second year. “

Dr Watkins said this year’s event is not expected to be as strong as the 2010-12 event and may even be weaker than the La Niña 2020-21 event.

“Each La Niña has different impacts, as it is not the only climatic factor affecting Australia at some point.

“That’s why it’s important not to look at it in isolation and to use the Office’s climate outlook tools online to get a sense of the likely conditions for the coming months,” Dr Watkins said.

The Bureau had previously moved to La Niña WATCH on September 14, 2021 and to La Niña ALERT on October 12, 2021. La Niña is expected to persist at least until the end of January 2022, with climate models suggesting this La Niña will be short-lived. , persisting until late southern hemisphere summer or early fall 2022.

The office said several indicators from the El Niño Southern Oscillation (ENSO) now show clear La Niña patterns. Sea surface temperatures in the tropical Pacific are near La Niña thresholds, with climate model prospects expecting them to cool further. In the atmosphere, cloud and wind patterns are typical of La Niña, indicating that the atmosphere is now reacting and reinforcing the changes observed in the ocean.

The Indian Ocean Negative Dipole (IOD) is nearing its end, with ocean index values ​​in the neutral range. However, the cloud and wind pattern in the eastern Indian Ocean suggests that some influence of IOD remains. All models indicate that the IOD will remain neutral over the next several months, in line with its typical seasonal cycle. A negative IOD increases the chances of above average spring precipitation for much of southern and eastern Australia.

The Madden-Julian Oscillation (MJO) is currently over the Maritime Continent region at low to moderate force. The MJO is expected to progress eastward across the Maritime Continent and into the Western Pacific over the next fortnight, increasing the chances of above-average precipitation in northern Australia and the Maritime Continent, to the north from Australia.

The southern ring mode (SAM) has generally been positive for several weeks. It should remain at positive levels until the end of the year. A positive SAM during the summer generally brings wetter weather to eastern parts of Australia, but drier than average conditions for western Tasmania.

Climate change continues to influence the Australian and global climate. Australia’s climate warmed by around 1.44 ° C for the period 1910-2019. Precipitation in northern Australia during its rainy season (October-April) has increased since the late 1990s. In recent decades, there has been a trend for a greater proportion of precipitation coming from short duration and heavy rainfall events, particularly in northern Australia.

Download the audio of today’s press conference here.

For more information on climatic factors, visit the office’s website.