Frost risk on the rise despite warmer climate
GroundCover™ Supplement Issue: 109 | 03 Mar 2014
An increase in the number of frosts later in the season means more growers are reassessing sowing dates and varieties
It is a cruel paradox that although Australia’s climate is warming, the number of frost days and the length of the frost season have increased across much of the Australian grainbelt (Figure 1).
CSIRO analysis of climate data between 1960 and 2011 suggests the increasing frost incidence is due to the presence of more highs centred further south (37.5°S) and further west (125°E) and to the existence of more El Niño conditions during this period.
CSIRO climate application scientist Dr Steven Crimp says the southern shifting highs bring air masses from further south than in the past. This air is very cold and leads to extensive frosts.
“We think this so-called ‘southward displacement’ is what is driving the changing frost patterns,” Dr Crimp says.
Modelling work indicates that the increased incidence of frosts in August is likely to remain around current levels until the mid-2030s.
“By gaining a better understanding of the drivers of frost we will be in a better position to develop frost forecasting tools.”
Along with an increased incidence of frosts between August and November there has also been a shift to frost occurring later in the year.
“Many people think the increase in frosts is due to dry conditions, but frost events over the past decade have included some very wet years,” Dr Crimp says.
“Even though we are in a warming trend, we have this surprising change in frost risk. In the east, the window of frost occurrence has widened, so frosts are occurring earlier in the season and much later in the season. As we move to the west there is less occurrence of earlier frosts and it is more of a shift to frosts later into the season.”
The frost window has lengthened by three weeks in the Victorian grainbelt and by two weeks in the New South Wales grainbelt. Western Australia has, statistically, remained the same, while eastern South Australian sites are similar to Victoria, and sites in the west of SA are more like WA.
Northern Victoria seems to be the epicentre of the change in frost occurrence. Analysis of long-term temperature data for Longerenong in the Victorian Wimmera indicates the incidence of moderate (2ºC) and extreme (0ºC) frosts during the wheat flowering window has increased in the past 15 years (Figure 2).
Dr Crimp and his team found the frost window over much of northern Victoria had lengthened considerably in the decade to 2011. “If you look at the risk of experiencing a 2ºC minimum temperature event, the 10 per cent risk now occurs 46 days later than in any of the previous decades. The frost window over this past decade has been much wider than farmers have experienced before.”
More information:Dr Steven Crimp,
02 6246 4095,
Queensland Alliance for Agriculture and Food Innovation,
07 4639 8813,
GRDC Project Code MCV00010, UQ00071
Region National, North, South, West
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