Global heating in the Indian Ocean has shifted a climate pattern towards drier conditions across Australia’s globally important wheat belt causing a severe drop in yields over the past three decades, according to a new study.
Scientists from Australia and China warned as global heating continues, wheat-growing conditions would become more challenging.
The study, published in Nature Food, analysed different climate phenomena that influenced Australia’s rainfall since the late 1800s and used models to see how this affected wheat yields.
Global heating has caused a shift in a climate pattern known as the Indian Ocean Dipole which, when it’s in a positive phase, can starve wheat growers of rain.
The number of positive IOD events had risen markedly in recent decades, corresponding with a drop in rainfall and falling yields.
In good years, the average wheat yield could reach 2.5 tonnes a hectare but in drier years with positive IOD events, the yield would drop well below 1.5 tonnes a hectare.
The researchers used models that account for other factors that can influence wheat yield, such as crop management, sowing time, or the varieties planted.
The study comes as Australia is being heavily affected by the alternate negative phase of the IOD that is contributing to major downpours across the south and east of the continent.
A lead author of the study, Dr Bin Wang, a climate research scientist at the New South Wales government’s Department of Primary Industries, said: “The Australian wheat crop totally depends on rainfall. A positive IOD typically sees below average winter and spring rainfall. That means the wheat yield is decreased.
“The climate warming is a major driver in bringing more occurrences of these positive IOD events.”
Dr Andrew King, a co-author of the study at the University of Melbourne, said research had shown the Indian Ocean was warming quickly and this was caused by emissions of greenhouse gases.
The areas in Australia most influenced by those positive IOD events overlapped the areas where wheat is grown.
“We would expect wheat farmers to feel more challenging conditions in the future than they have in the past,” he said.
The study found positive IOD events had become stronger than before and this had seen it take greater influence over wheat yields than other climate systems, such as El Niño or La Niña.
As greenhouse gases continue to rise in the atmosphere, this would probably see more positive IOD events causing more droughts.
Australia is one of the world’s major exporters of wheat, accounting for more than 10% of the global trade.
The country’s wheat belt includes south-west Western Australia, south-east South Australia, western Victoria and swathes of central New South Wales and Queensland, west of the Great Dividing Range.
Farmer Peter Holding, who grows wheat and canola in Harden in NSW, sold about nine-tenths of his property in the 2000s “because the droughts beat us”.
Holding, who also works with campaign group Farmers for Climate Action, said improvements in wheat varieties, chemicals and fertilisers, and greater understanding of soils had meant yields had been held steady.
“Basically we’ve been running harder to stand still. What’s happening with climate change is that the extremes are getting more extreme,” he said.
“That’s quite worrying. We’re just not getting those average years. The averages have disappeared and the extremes have become the norm.”
According to forecasts from the Australian Bureau of Agricultural and Resource Economics and Sciences (ABARES), 2022-23 could be the second-biggest wheat harvest on record.
But ABARES warns the negative IOD and a third consecutive La Niña – a system also linked to higher rainfall – could make conditions too wet, causing downgrades in wheat quality and a delay in harvesting.
In other wheat-growing regions such as southern parts of the United States, southern Brazil and Argentina, La Niña means drier conditions, which could have “implications for global grain production over the coming year”, ABARES has said.
Holding said the conditions for some farmers were now “too wet” but he expected conditions to “flip, and flip hard” to drought in the coming years “and that’s going to be really tough”.
Brett Hosking, chair of industry group GrainGrowers, said regardless of any models “growers farm to the conditions in the paddock and need access to world-class varieties to keep pace with climate variability and a growing need for food”.
He said there was significant variation across the country’s growing regions and the effects of IOD and the cycle of La Niña and El Niño were not the same everywhere.
He said wheat yields were increasing “due to the ingenuity of growers” coupled with research, adding: “Growers continue to adapt and produce crops despite the challenges thrown at them.”
Technology and improved modelling and forecasting “will continue to be vital as both growers and those in research and development adapt to challenges”.
