WHEN agriculture in eastern Australia is in strife, an El Nino event is often hanging around.
This time, there is no El Nino, but the drought stress on landholders through NSW and Queensland is acute. What’s going on?
Bureau of Meterology climatologist Lyn Bettio offers two answers: “heat” and “don’t know”.
Heat, because Australia has experienced its hottest year on record, amplifying evaporation rates and minimising the benefit of any rainfall that has fallen on parched land.
Don’t know, because climate scientists are still trying to work out what’s causing the absence of rainfall over vast chunks of eastern Australia.
The usual climate drivers aren’t in evidence. Around the continent, the oceans that breed Australia’s weather are in a neutral state - not unusually warm, not unusually cool, just around average.
Unfortunately, Dr Bettio said, for reasons not yet understood, that isn’t producing “average” weather.
After a destructively wet cycle, the failure of the 2012-13 monsoon kicked off a year of hot, dry conditions - and not coincidentally, poor cattle prices.
Mt Isa recorded its driest year on record. Just 86mm fell on the north-western Queensland town in 2013.
National Climate Centre climatologist Blair Trewin reported on www.theconversation.com that for large parts of inland Queensland, 2013 was the among the driest 10 per cent of years on record.
Dr Bettio said that for NSW, the 18 months from August 2013-January 2014 was the fifth driest such period on record.
Such low rainfall is depressing, but it is within the bounds of normal variability in Australia’s naturally highly variable climate.
Temperature, on the other hand, has been well outside natural variability. Last year was the hottest year recorded in Australia, 1.2C warmer than the 1961-1990 average.
The record heatwaves of early 2013 and 2014 made the news, but the more exceptional conditions were recorded in September, when Australian temperatures were 2.7C above the mean.
As Dr Trewin and other climatologists wrote on The Conversation, September 2013 temperatures were those of an average November.
Dr Bettio said these figures are in agreement with other temperature trends from a warming world. What’s less clear is temperature’s relation to rainfall in northern latitudes.
In south-eastern and south-western Australia, climate models show a clear signal between rising temperatures and decreased rainfall over the long-term.
Over northern NSW and southern Qld, that clarity isn’t there.
That makes it difficult to point to a culprit behind the current drought, Dr Bettio said. And without a culprit, it is impossible to forecast when drought might abate.
Ex-Tropical Cyclone Dylan, which crossed the Queensland coast near Bowen on Friday morning and weakened into tropical low, offers some promise of breaking the cycle, but that promise has been extended before, and not delivered.