Two separate climate systems are conspiring to bring a wet and warm end to winter, the Bureau of Meteorology has forecast. After a calm few months, the Indian Ocean Dipole and La Nina are brewing, seeing a dramatic change in the weather over the coming months. La Nina’s last appearance earlier this year led to massive floods across the country’s east. Widespread floods in the southeast are now a real possibility again, but there is no indication yet of how serious they might be should they occur.
The Bureau’s climate outlook for August to October, released in recent days, also included a look back on the current conditions. Last month there was record-breaking rain in southwest Western Australia. Perth is expected to have had its wettest July in over two decades. The north of Australia was warmer than average during the first two months of winter, with the southeast of the country cooler. Adelaide saw its coldest day on record on July 22, with the mercury not reaching even 10C. But those chilly temperatures will soon be long gone with warmer-than-average days and particularly nights for the coming months.
Climate drivers cranking up
The Indian Ocean Dipole (IOD) and El-Nino Southern Oscillation (ENSO) climate drivers are the causes. Both are a measure of sea surface temperatures aided by powerful trade winds. The IOD, as the name suggests, is centered on the Indian Ocean and ENSO in the Pacific. How these temperatures rise and fall can significantly affect rainfall in Australia, Africa, and the Americas. Generally, if it’s wetter than usual in Australia, it will be drier in either or both of the other two continents. “In the Indian Ocean, a negative IOD has developed, bringing warm ocean waters to the north and northwest of Australia and typically enhancing winter and spring rainfall over much of southern and eastern Australia,” said Dr. Paul Feikema, a senior hydrologist with the BOM.
That’s combined with a lowering of water temperatures in a patch of the Pacific Ocean, which is crucial in forming positive or negative ENSO conditions – the latter known as a La Nina. A La Nina occurs when trade winds increase, hauling calmer waters from the ocean’s depths to the eastern Pacific’s surface. These stronger east-to-west winds also push warmer seas closer to Australia. That aids in the creation of more clouds and so moisture and windier conditions for the continent. “Some models indicate this cooling could be sufficient to reach La Nina levels during spring,” Dr. Feikema said. “However, even if La Nina levels are not reached (and ENSO remains neutral), this cooling may strengthen the wet outlook for much of Australia. As a result, the August to October outlook suggests above-average rainfall is very likely across much of the country.”
Flooding is a ‘possibility.’
Already sodden catchments mean widespread flooding is a real possibility across southeastern parts of the country in the coming months. However, the increased rainfall is less likely to occur in southwest WA, bringing a reprieve from the constant rain in Perth. Southern Victoria and much of Tasmania may also miss out. As for temperatures, days are likely to be warmer than average across Tasmania, Victoria, coastal New South Wales, and southern parts of South Australia, as well as the nation’s north. But nights are likely to be warmer across almost the country, except southwest Western Australia. The Bureau added that Australia’s climate has warmed by around 1.44C from 1910–2019, while southern Australia had seen a 10–20 percent reduction in excellent season rainfall in recent decades.
