Drought deepens as ‘very dry winter’ combines with record heat
By Peter Hannam
Drought-hit regions of southern and eastern Australia got little if any relief during winter, with barely half the normal rainfall and the country still posting its warmest start to any year for daytime temperatures.
The Bureau of Meteorology’s winter summary showed the country had its sixth-warmest June-August for maximum temperatures, while rainfall averages were the least – at 36.4 millimetres – since 2002. For the first eight months of 2019, maximums are running the hottest on record and mean temperatures the second-warmest.
“It was a very dry winter over the bulk of the continent,” said Blair Trewin, the bureau’s senior climatologist, adding that south-eastern Australia was on course for a third relatively dry April-September cool season in a row.
The Murray-Darling Basin, Australia’s food bowl, had yet another poor season, with less than half its typical rain. The average of 48.4 millimetres was its fourth lowest in more than a century of records.
NSW was particularly dry with about a third of its usual winter rain, and the least since 1982 as high-pressure systems dominated the state. Daytime temperatures were the fifth mildest on record – or about 1.44 degrees above average – with each of the past three winters now among the top 10 hottest.
Sydney had its third-warmest winter on record – at almost 2 degrees above the norm – for daytime readings. The eight days in a row above 20 degrees marked a July record for the Harbour City, and its year-to-date average maximum of 23.6 degrees is the hottest for any January-August period on record.
Strong westerlies meant Victoria had a less extreme winter than parts further north, with rainfall just 11 per cent below the norm and average temperatures about half a degree above average.
So far this year, Victoria is running at about the third-warmest for mean temperatures, the bureau said.
“It’s been wet in the southern part of the state, especially west of Melbourne,” Dr Trewin said. “It’s been dry, though, in the far north-west and parts of central and east Gippsland.”
Comparisons for Melbourne itself are more difficult because of a change of its monitoring site, with readings at the Olympic Park location dating only from 2013. Greater Melbourne, though, was generally warmer than average during winter despite several bursts of cold that included snow in the Dandenong Ranges.
Consequences of the poor rains include ongoing hardship for farmers but also rising concern about the availability of water in fast-drying catchments. Sydney, for instance, had its second-lowest winter runoff on record as parched soils soaked up much of the meagre rainfall.
While climate change contributes to the background warming of Australia – temperatures have risen almost a degree over the past century – the immediate drivers are also not promising as far as the prospects for drought-breaking weather go.
One source of moisture for inland Australia is the Indian Ocean but relatively cool conditions off Western Australia have turned much of that tap off. The gauge of such conditions, known as the Indian Ocean Dipole, has been in its positive phase since about May and is expected to become more so in coming months, international models used by the bureau show.
Conditions to the south, though, contributed to weather patterns that at least brought some rains to the southern edge of the nation and Tasmania.
The so-called Southern Annular Mode, which gauges the westerly belt of winds circulating Antarctica, has lately been in its negative phase.
That means the storm tracks have shifted towards the equator in their west-to-east movement. The strong upper level jetstream, for instance, is closer to about 45-50 degrees south rather than 55-60 degrees, Eun-Pa Lim, a senior research scientist at the bureau said.
The bureau’s outlook for the next three months remains for most of Australia to be warmer and drier than average.
Also being closely watched is a so-called sudden stratospheric warming event over the Antarctic region. While such events in the northern hemisphere are usually accompanied by big chills, such as in Europe, the same is not the case for Australia, Dr Trewin said. Storms, though, may nudge further north, such as to New Zealand or possibly Tasmania.