Climate Change

Australia shivers as winter ends; spring to be wet due to negative Indian Ocean Dipole, La Nina

The Bureau of Meteorology recently stated that its three-month climate outlook was of above average rainfall for much of Australia, particularly for the central and eastern states

By Rajat Ghai
Published: Wednesday 10 August 2022

A screengrab showing snowfall on Bluff Knoll, the highest peak in southern Western Australia on the morning of August 9, 2022A screengrab showing snowfall on Bluff Knoll, the highest peak in southern Western Australia on the morning of August 9, 2022

Australia is witnessing a second cold blast after its coldest July in a decade. The continent, which is in the throes of the southern winter, could also be in for a wet spring after meteorological authorities confirmed that a negative Indian Ocean Dipole (IOD) was underway.

The Bureau of Meteorology (BOM), which comes under the federal Australian government, stated last week, that its three-month climate outlook was “of above average rainfall for much of Australia, particularly for the central and eastern states.”

“With wet soils, high rivers and full dams, and the outlook for above average rainfall, elevated flood risk remains for eastern Australia,” Andrew Watkins, the Bureau of Meteorology’s head of long-range forecasting, was quoted as saying.

According to the BOM, the IOD describes a natural climate cycle brought about by sustained changes in the difference between sea surface temperatures of the tropical western and eastern Indian Ocean.

Andrew King, a senior lecturer in climate science at the University of Melbourne, recently wrote for The Conversation:

Warm waters in the east Indian Ocean, like we’re seeing at the moment, increase the occurrence of low pressure systems over the south-east of Australia as well as the amount of moisture in the air.

This means there’s a higher likelihood of rain generally and an increased chance of extreme rain events too, he added.

But will this become a regular phenomenon? “Oceans around Australia are acidifying and have warmed by around 1°C since 1910, contributing to longer and more frequent marine heatwaves,” the BOM’s State of the Climate 2020 had noted.

Roxy Matthew Koll, a climate scientist with the Indian Institute of Tropical Meterology, Pune, told Down To Earth:

As the oceans warm, extreme positive IOD events are projected to increase by almost a factor of three by the end of the 21st century. However, the climate models used to make these projections have significant biases in representing the distribution of sea surface temperatures. Hence the projected increase in extreme positive IOD events is debatable.

“It is shown that the rise in extreme IOD events could stabilise if the global mean temperature is kept under 1.5-2.0°C warming by 2050,” he added.

The other factor that could cause a wet spring is the La Nina weather phenomenon. The BOM, in its ‘Climate Driver Update’ released August 2, said:

The Bureau’s ENSO Outlook remains at La Niña WATCH, meaning there is around a 50 per cent chance (double the normal likelihood) of La Niña forming later in 2022. This is a result of current observations and model outlooks.

“La Niña events increase the chance of above average winter–spring rainfall across much of northern and eastern Australia,” it added. The La Nina phenomenon in the equatorial Pacific Ocean is the opposite of El Nino. La Ninas generally have a cooling effect on global temperatures.

There have already been back-to-back La Nina events in the recent past.

King noted in The Conversation article that “Three La Niña events in a row is not unprecedented but it is unusual. The increased chance of another La Niña raises the odds of wetter conditions persisting for a few more months at least.”

Wet and cold

Meanwhile, it has been damp and wet across Australia in the past few days. The BOM tweeted August 8 that a cold front would sweep across south-west Western Australia, bringing rain, isolated thunderstorms, strong winds and colder temperatures.

It also said that there was a likelihood of snow in the state, which is a rare event.

The BOM also said flood warnings remained in place for inland New South Wales and north-east Victoria states. “Rain is expected to return to south-east Australia later this week due to a front and low-pressure system moving across Australia,” it added.

Perth, Western Australia’s main city, shivered August 9 as the cold front from the Southern Ocean moved in. The temperature at Perth’s main weather station was 9ºC at midday August 9, according to media reports.

“This is equal to the city’s average overnight minimum temperature at this time of year and a whopping 9ºC below its average August maximum temperature,” website reported.

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