Comparative seasonal rainfall maps released on 24 February 2016 by the Australian Export Grains Innovation Centre (AEGIC) show that a new climate is emerging in Australia.
AEGIC researchers analysed data from more than 8,000 Bureau of Meteorology (BoM) stations across Australia and found that rainfall zones nationwide have changed significantly since the turn of the 21st century.
The findings were presented by AEGIC agro-meteorologist Dr David Stephens at the 2016 GRDC Perth Grains Research Update as part of a talk entitled ‘South-west Western Australa is losing its Mediterranean Climate’.
The new analysis has uncovered dramatic changes to Australia’s climate over the past 16 years, Dr Stephens said.
“Since 2000, there has been a general increase in summer rainfall across Australia and a corresponding decrease in winter rainfall, leading to shifts in rainfall zones extending for hundreds of kilometres,” he noted.
“Rainfall between May to October over much of the heavily populated regions of southern Australia has decreased 10 to 30 percent, while summer rain has increased up to 40 percent in some areas.
“This change in climate has major implications for farming and pastoral systems as the profitability of different crop type changes, disease risk changes, and the composition of rangeland grasses changes with stocking rates,” Dr Stephens said.
IMPLICATIONS OF THE NEW RAINFALL PATTERN
1. Winter crops sown earlier will do better across key grain-growing regions
AEGIC’s analysis highlights the need for Australian grain growers to change their schedules to allow for earlier sowing of winter crops, says Dr Stephens. Earlier-sowing regimes were measured by AEGIC recently and found to be a successful strategy.
It’s a strategy that could prove even more productive if the new pattern – less winter rainfall across many of the main grain-growing regions of Australia –.continues.
Earlier sowing of winter crops should continue, for a number of reasons, Dr Stephens asserted.
Early-sown crops can take advantage of additional soil moisture in summer. “They also experience a lower evaporative demand through the growing season, and are less affected by declining rain in October and rising spring temperatures,” he said.
2. Perennial tropical crops could replace temperate grass crops in parts of WA and Queensland
“In pastoral regions in much of Western Australia, increasing summer rain with a reduction in rainfall variability has assisted perennial C4 (tropical) plants at the expense of C3 (temperate) grasses (especially in southern areas), while in central and northern Queensland, an increase in rainfall variability has been detrimental on pasture production and stocking rates,” Dr Stephens explained.
3. Water-efficient farming systems will be crucial across southern Australia
“Australia is going to need some of the most water-efficient farming systems in the world to mitigate the effects of a drier and warmer climate in southern Australia," Dr Stephens contended.
“Research in this area is vital because Australian crop yields have been among the most affected by climate change compared to other grain-exporting nations,” Dr Stephens said.
BACKGROUND TO THE CHANGING RAINFALL PATTERNS
Key changes in rainfall zones across Australia between 2000 and 2015
- In regions with a Mediterranean climate, winter (and winter-dominant) rainfall zones are contracting in a south-westerly direction.
- In northern and eastern areas, summer (and summer dominant) rainfall zones are expanding southward.
- Between these regions lies a ‘uniform rainfall zone’ in which rainfall varies little between summer and winter. The southern boundary of this zone has shifted significantly, from southern/central New South Wales into central Victoria and the Mallee region of south-east South Australia.
- Since 2000, a uniform rainfall zone has appeared along the eastern edge of the wheat-belt in south-west Western Australia, extending from Beacon to Southern Cross to Grass Patch.
- Typically, Australia’s rainfall zone boundaries have shifted by between 100 and 400 kilometres over the past 16 years.
- The winter rainfall zone has expanded only in south-eastern Tasmania, a region in which winter rainfall has become more reliable since 2000.
Why the change in rainfall zones?
It appears that the shift in rainfall zones, as shown in the AEGIC maps, relates to changes in a number of factors, including barometric pressure, sea surface temperatures and upper-level westerly winds.
The mid-1970s brought a weakening of the Indian Ocean Trough west of Perth that appears to be associated with lessening winter rainfall. Since 2000, this trough has weakened further. Over the same time frame, high pressure systems over Australia have strengthened, and sea surface temperatures have warmed across all seasons, promoting greater summer rainfall.
A marked warming of winter-time temperatures in the Indian Ocean west of Perth, inversely associated with rainfall, has contributed to weaker cloud-band activity across Australia in recent years.
At a hemispheric scale, the temperature gradient between the equator and the South Pole – an important driver of weather – dropped in the early years of the 21st century as May-July westerlies weakened over Australia.
Variability in annual rainfall across Australia has also changed since 2000.
There has been a reduction in rainfall variability in some regions, notably south-western Australia, due to the loss of wet years; and more consistent average-to-above-average rainfall in others, principally Australia’s north-west and the southern part of South Australia.
In contrast, annual rainfall has become more variable across inland Victoria, southern New South Wales and much of central Queensland.
For more information, contact AEGIC’s Keir Tunbridge on 0438 632 463 or at email@example.com.