THE climate pattern that brought average – and in many cases above average – rains to the eastern Australian cropping belt over winter and early spring is likely to continue through well into spring.

The collapse of a long-running El Nino in autumn has seen much of the eastern farming zone soaked by a series of rain events that have been beneficial for winter crops in many instances, but caused devastating waterlogging and disease losses in the harder hit areas.

The outlook for both the east and west of the continent is for average rainfall conditions to continue through to the end of the winter cropping season.

University of Southern Queensland senior climate scientist, Dave McRae, Toowoomba, said the climate in eastern Australia had moved from an El Nino pattern into a ‘neutral’ phase which meant producers could expect ‘average’ rainfall conditions to persist for some time yet.

“If we look across the cropping zones of eastern Australia, realistically it is an average outlook. Using the SOI phase system, there is roughly around a 50 to 60 per cent chance of getting above median rainfall through to the end of November,” he said.

“If you look at the global circulation models, generally speaking the majority are in agreement with that.

“The outlook is smack bang down the middle. For those cropping areas that are already exceptionally wet, ‘average rainfall’ is probably not what they want. They would like weeks of dry, windy, sunny weather.”

Increased storm activity

Mr McRae said the current climate pattern was also associated with an increased risk of storm activity.

“The thing that stands out at the moment, especially for southern Queensland and northern NSW, in a neutral SOI phase pattern there is an increase in the risk of severe storm activity for spring and early summer. With that you get an associated increase in hail risk,” he said.

“It doesn’t occur in La Nina or El Nino years. It is just a reflection of the fact we are in a neutral pattern and we have a neutral SOI phase.”

El Nino breakdown

Mr McRae said the breakdown of the El Nino in autumn had ended a long period of dry weather for eastern Australia.

“Over the last few years we have been in a relatively strong El Nino event that has led to below average rainfall over the past three years across eastern Australia. Victoria, Tasmania, parts of NSW and much of Queensland had well below average rainfall during that period,” he said.

“But, in autumn/early winter this year the strong El Nino pattern broke down, or flipped out. That isn’t unusual, because if it is going to do it that is the time of year you expect it to occur.

“One of the rules of thumb we have when you have a flip out of a strong El Nino is that often, not always, you will get well above average rainfall during that following winter/early spring. That has certainly been the case this year.”

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Mr McRae said another factor behind the wet conditions over winter had been the warmer-than-normal sea surface temperatures around north-west and eastern Australia.

“What that has done is help with the inflow of moisture across the Continent, both from the east and the west. That has contributed to the well above average rainfall,” he said.

Frost risk

In the West, Bureau of Meteorology media and communication manager, Neil Bennett, Perth, said while the outlook was for an average rainfall finish to the winter cropping season in Western Australia, the main concern now was the risk of frost.

“Temperatures in September have been below average across the south west. That is leading to worries for overnight temperatures. We have had some frost events and we have another frost event coming this weekend,” he said.

Mr Bennett said until now the season had been average across the WA cropping belt, despite some growers feeling it had been exceptionally wet.

“It is surprising how farmers are saying it has been one of the wettest winters they can remember, but the statistics are showing the winter wasn’t an exceptionally wet one, apart from along the south coast where the rainfall was above average. For many parts, it was either average or a little bit below average,” he said.

“The thing that has helped farmers a lot is we had some very good rainfall coming out of autumn that set the subsoil moisture really nicely.”

Regular rainfall pattern

Mr Bennett said compared to previous winters in south-west WA there were no prolonged dry spells this year. Through June, July and August the rains came through in regular patterns.

He said the Indian Ocean Dipole, plus the strength of the high pressure system subtropical ridge through the West, were the key drivers behind the change to the rainfall pattern.

“When we have prolonged dry spells, the ridge tends to sit further south than its normal winter position and it tends to block off the cold fronts. That didn’t happen this year. It sat in a more typical winter position where the ridge access was north of Perth and that allowed the westerly flow to become established, with cold fronts moving up from the Southern Ocean,” he said.

“We also had a lot of interactions of north-west cloud bands moving down over the grain growing area. It was perfect rain, not short and sharp but slow and steady.”

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