La Niña will shape the Australian summer 2021-22 with above-average precipitation forecasts for the eastern parts of the continent; Increase flood risk. Most of Australia, except in parts of the southeast, should expect above-average summer highs.
This explainer distills the latest advice from the Bureau of Meteorology on what to expect this summer. It takes stock of extreme weather risks, takes a close look at the effects of La Niña – the dominant climate driver influencing our weather today – and puts everything in the context of our changing climate.
What is La Niña and how will it shape the summer of 2021-22 in Australia?
The Bureau of Meteorology stated that a La Niña is underway on November 23, 2021. Australia’s weather is influenced by a number of “climate drivers” including the El Niño Southern Oscillation, the Indian Ocean Dipole, the Southern Annular Mode and the Madden-Julian Oscillation. These are cyclical fluctuations in sea surface temperatures and ocean-atmosphere interactions in the Pacific Ocean, Indian Ocean, Southern Ocean and the tropics. They influence the annual fluctuations in temperature, precipitation and other weather patterns.
La Niña is a phase of the Southern Oscillation of El Niño. It occurs when equatorial trade winds get stronger; Bring cooler water up from deeper ocean depths. This leads to a cooling of the surface of the central and eastern tropical Pacific. The stronger trade winds also help warm surface water to accumulate in the western Pacific and north of Australia. These warmer water in the Western Pacific means more clouds will develop when warm, humid air rises. This can lead to heavy rainfall in northern Australia.
Every La Niña event is different, as the effects of La Niña can be amplified or dampened by the other climate drivers.
The current La Niña is expected to last until late summer or early autumn 2022. However, there are reasons to expect that this La Niña will not be as disruptive as the exceptionally strong 2010-12 event, including the fact that the 2010-12 La Niña coincided with a negative phase of the dipole in the Indian Ocean. This enhances the effect of La Niña. At the moment the dipole in the Indian Ocean is in a neutral phase.
However, Southern Annular Mode (SAM) is expected to remain positive through the end of the year. The La Niña conditions in the Pacific Ocean and the positive SAM phase influence the above-average precipitation prospects. Please see BoM’s latest Climate Driver Update for more information.
According to the Bureau of Meteorology (summer) projections from December to February and in line with typical La Niña conditions, rainfall between December and February should be above average in eastern Australia, particularly in the eastern parts of Queensland.
The odds are stacked (1.5 to 3 times more likely) in favor of some unusually high maximum temperatures for most of the country outside the southeast. Sub-average daytime temperatures are likely for eastern NSW.
What extreme weather risks do we see this summer?
The Bureau of Meteorology’s 2021-22 Summer Outlook shows that the eastern parts of the continent will likely be above average humidity, with a higher risk of heavy rainfall and widespread flooding for those areas.
When it comes to cyclones, there are typically more cyclones in the Australian region during the La Niña years than during the non-La Niña years. There were several notable cyclones during La Niña 2010-12, including Cyclone Yasi – one of the most powerful and expensive in Australian history. Any year that Queensland had more than one major tropical cyclone was a La Niña year. The Bureau of Meteorology has forecast an average to slightly above average number of cyclones for the 2021/22 season.
What does this mean for bushfire risks?
Above-average rainfall may be good news when it comes to reducing the risk of bushfires. However, rain in spring and early summer means a lot of grass growth. If these grasses dry out quickly in warm weather, the risk of rapidly escalating grass fires increases.
The Bureau of Meteorology has warned that we must watch out for grass and crop fires in the summer of 2021-22, especially inland and in the southwest of the country, where we had high grass growth in winter and spring.
All in all, 2021-22 is unlikely to repeat the dire conditions we experienced in the run-up to and during the Black Summer, although we mustn’t be complacent. Unfortunately, due to accelerating climate change, we have entered a new era with greater risk of fire and we need to be even more vigilant than before.
How is all of this related to climate change?
While the La Niña event will affect our weather this summer, it is important to remember that these short-term cyclical factors are now occurring in the context of global warming.
Australia’s temperature and rainfall variability is also affected by global warming caused by human activities, primarily the burning of coal, oil and gas, as well as land use changes such as deforestation. All weather now occurs in an atmosphere that is warmer, more humid, and more energetic. Australia’s climate warmed by around 1.44 ° C between 1910 and 2019. A warmer atmosphere can absorb more water vapor – seven percent more per degree of warming. A warmer and more humid atmosphere also provides more energy for weather systems that generate heavy rainfall. This means that while climate change can only lead to a modest increase in the total amount of precipitation worldwide – limited by the moisture retention capacity of the atmosphere – it leads to a dramatic increase in the heaviest and most damaging rainfall. In the past few decades, and particularly in Northern Australia, much of our rain has come in the form of short, intense rains. This trend will continue and increase the risk of dangerous flooding.
Ignoring climate change is expensive
Australians are already paying the price for the carbon pollution that has been added to the atmosphere over the past two centuries.
The cost of extreme weather disasters in Australia has more than doubled since the 1970s, reaching $ 35 billion in the 2010-2019 decade. Queensland bears the highest burden of total damage to the state from extreme weather disasters since the 1970s, about three times that of Victoria and about 50% more than NSW. On a person basis, Queensland’s losses were more than double the national average.
For more information, see the Climate Council report “Hitting Home: The Compound Costs of Climate Inaction”.
Governments like the Australian government, which have failed to cut emissions in the past decade, have condemned Australians and communities around the world to a much more dangerous future than if they had heeded repeated warnings from scientists. Because of this past inactivity, gradual, measured steps are no longer sufficient to avoid a catastrophe. This is where truly transformative action is needed. This means halving global emissions at least in half over the next ten years and achieving net zero emissions worldwide by 2040 at the latest. As an industrialized country with great potential for renewable energy, Australia should reduce its emissions by 75% by 2030 and reach net zero by 2035.
No developed country has more to lose from climate change-induced extreme weather conditions or more to gain as the world transforms into a carbon-free economy than Australia. It is in the interests of all of us to do more urgently and quickly to reduce emissions.
For more information, see Aim High, Go Fast: Why Emissions Need to Plummet This Decade, the Climate Council’s science-based vision of what Australia’s best efforts might look like.
Stay safe this summer
Everyone stay healthy, and if you haven’t already, contact your state / territory fire and emergency department for advice on how to deal with the extreme weather risks of summer.