Meteorologists around the world, including Australia, have warned for months that La Nia conditions are forming in the Pacific Ocean, and Tuesday’s announcement means parts of the country are on alert for possible flooding and an increase in tropical cyclones.
“In terms of tropical cyclones, for La Nia, we see a higher-than-average — probably about a 65% chance of seeing a higher-than-average number of 11 tropical cyclones,” said Andrew Watkins, head of the Bureau of Operations Climate Services, at a news conference. said in.
Those same parts of the country already have wet soil, clogged rivers and high catchment areas for long periods of rain.
“Further rains increase the risk of widespread flooding, typically in southeastern Australia,” he said.
The news dashes the plans of millions of Australians planning local beach holidays over the Christmas summer period, many of whom have recently emerged from lockdowns during the pandemic.
But La Nia brings some advantages, including cooler temperatures in the summer, which can typically rise above 30 °C (86 °F).
“The good news about La Nia is that it reduces the risk of bushfires,” Watkins said. “At least in the context of those big wildfires that we saw a few years ago, the risk is reduced.”
La Nia usually occurs at intervals of between a few years and a decade, and typically lasts for a year or two, but has formed on the heels of each other.
What is La Nina?
La Nia is part of a natural cycle called the El Nio Southern Oscillation – or ENSO, and occurs when cold water forms on the west coast of the South American continent.
Pulled by strong easterly winds, the cold water moves west into the Pacific, forming a “cold tongue”. This moves the hot water and consequently high pressure system. The resulting weather system — filled with warm, water-filled air — produces unusually heavy rains when it makes landfall.
Its effects are different in different parts of the world.
For example, in the Americas, La Nia generally brings wetter and cooler conditions in the Pacific Northwest and Northern Plains, but it brings drier and warmer-than-average conditions in the southern states, exacerbating drought in some regions there. could.
In the context of Australia, cooler waters in the central and eastern tropical Pacific, along with strong and persistent southeast to northwest winds, help move clouds closer to the country to the west, BoM explained.
“The last significant La Nia was 2010-12. This strong event saw major impacts across Australia, including Australia’s two-year period on record and widespread flooding,” Watkins said.
A link to climate change?
The extent to which global warming has contributed to the intensity of La Nia is still not known, with records of this event only dating back 60 years.
El Nio and La Nia are events that occur naturally as part of Earth’s weather systems, but research is beginning to show that increased global temperatures can reverse or reverse their effects.
A 2018 study on atmospheric conditions simulated climate conditions and found that climate change can increase the severity of weather events stemming from El Nio patterns.
Outside of any impact on hurricanes, climate change could mean that some of the older temperature patterns associated with El Nio and La Nia no longer apply.
While La Nia cools temperatures, global warming is happening so rapidly, sometimes its effects are muted.
Long-term weather patterns across Australia are notoriously difficult to forecast, and the BoM is collecting oral evidence from Aboriginal Australians to better understand the continent’s weather cycles.
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