Australia’s Weather – a Two Year Summary
Annabelle Honner, Agfarm Freight Coordinator
September 2019
Over the last 24 months, all growing regions of Australia have experienced at least below average rainfall, with parts of north western NSW, SA Mallee, WA Esperance and northern Adelaide areas receiving their lowest rainfall on record. In fact, the BOM has defined parts of the Murray Darling basin as being in drought since January 2017. There is no question this has been a prolonged and intense drought, but the question is, why have we been in a drought for so long?
Image source: http://www.bom.gov.au/jsp/awap/rain/index.jsp?colour=colour&time=latest&step=0&map=decile&period=24month&area=nat
There have been a series of complicated and inter-connecting atmospheric weather events, particularly in the last 12 months, that have resulted in continued low rainfall across Australia, particularly in the eastern states. Throughout 2017, there were no strong climatic influences that were affecting Australia’s climate either way, until the end of 2017 and into the beginning of 2018, when we experienced a short-lived La Niña. Unfortunately, this event did not have a huge effect on rainfall in Australia. This decayed quite quickly and, although there were certain climatic indictors of El Niño, they were not long lived enough to constitute an El Niño event. Around October 2018, a negative Indian Ocean Dipole (IOD) formed, which lasted until mid-way through December. At the beginning of this year there were once again climatic signs of El Niño forming, but by June this year, another Positive IOD formed, which is still active.
The IOD is influenced by the difference in ocean temperatures between the west and east Indian Ocean. In a positive IOD year, these interactions generally result in moisture shifting away from Australia and being pulled towards the east coast of Africa and the Middle East. The IOD can impact anytime from May – December, where after the onset of the northern monsoon results in IOD being unable to form. In general, northern QLD, NT and WA’s rainfall onset occurs from November to early December, however predictions are indicating that any chances of rainfall onset occurring before November-December are unlikely, meaning the effects of the positive IOD may well be felt right up to the end of this year.
Image source: http://www.bom.gov.au/climate/rainfall-onset/
These rainfall outlooks also lay shaky foundations for the upcoming summer crop plant. Significant soil moisture deficits persist through NSW and QLD, and this combined with the lack of upcoming rainfall may well be enough to convince many growers to not sow a summer crop, and instead fallow their paddocks in hope for decent rain at the end of summer and into autumn to set them up for a 2020/21 winter crop. Furthermore, water availability for irrigation is becoming increasingly tighter, with ABARES forecasting water prices for the 2019/20 season to reach as high as $650/ML in southern NSW, VIC and SA, making irrigation an expensive option for most. In its most recent production report, ABARES has forecasted the area planted to sorghum to decrease by 28% from the 2018/19 plant to 391,000 ha, 30% below the 10-year average. They’ve also predicted area planted to cotton to be reduced by 58% to 145,000 ha. Despite a reduction in planting, lint yields are forecast to be average to higher, as nearly the whole crop planted will be irrigated. These summer crop outlooks reflect the poor soil moisture and continued outlook of unfavourable conditions.
Image source: http://www.bom.gov.au/climate/outlooks/#/rainfall/median/seasonal/0
These rainfall outlooks also lay shaky foundations for the upcoming summer crop plant. Significant soil moisture deficits persist through NSW and QLD, and this combined with the lack of upcoming rainfall may well be enough to convince many growers to not sow a summer crop, and instead fallow their paddocks in hope for decent rain at the end of summer and into autumn to set them up for a 2020/21 winter crop. Furthermore, water availability for irrigation is becoming increasingly tighter, with ABARES forecasting water prices for the 2019/20 season to reach as high as $650/ML in southern NSW, VIC and SA, making irrigation an expensive option for most. In its most recent production report, ABARES has forecasted the area planted to sorghum to decrease by 28% from the 2018/19 plant to 391,000 ha, 30% below the 10-year average. They’ve also predicted area planted to cotton to be reduced by 58% to 145,000 ha. Despite a reduction in planting, lint yields are forecast to be average to higher, as nearly the whole crop planted will be irrigated. These summer crop outlooks reflect the poor soil moisture and continued outlook of unfavourable conditions.
Image source: http://www.bom.gov.au/water/landscape/#/sm/Relative/day/-28.4/130.4/3/Point////2019/9/12/
The BOM defines ending rainfall deficiency (not necessarily breaking a drought) as the rainfall in the last month already exceeding the 30th percentile for the three-month period commencing that month, or if the rainfall for the past three months is above the 70th percentile for that period. Basically, above-average rainfall needs to happen for consecutive months for a drought to be broken. Unfortunately for now, the long-range three-month forecasts are not providing much hope that above average rainfall will be received, however once the positive IOD and the negative SAM have both broken down, hopefully weather patterns start turning around.
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