A change in climate is increasing the risk of frost events occurring in south-eastern Australia. Climate & Agricultural Support director Melissa Rebbeck says there has been a change in high pressure system movements in recent years.
“High pressure systems are usually centered over the Great Australian Bight during summer, and move up towards the centre of the country during autumn. This movement allows low pressure systems to take their place, influencing the development of cold fronts and rainfall. We’re now seeing the high pressure systems moving north later in autumn and returning south earlier in spring” she said.
Furthermore the high pressure systems are becoming larger than normal and taking longer to cross the continent. The late moving high pressure systems not only block the rainfall, they can also drag cold air in from the Antarctic.
“The 2014 frost events occurred when a very large high pressure system was unusually low and large, and dragged cold air in from the Antarctic and dropped it over southern and Eastern Australia. Because it was slow moving it caused 6 days of sub zero temperatures from almost dawn until dusk” Ms Rebbeck said.
The frost season is widening and the number of potential frost days is increasing despite an increase in average temperatures. Source: Steve Crimp, CSIRO.
Work by Dr Steven Crimp from CSIRO shows that since 1980 the frequency of very cool months has declined, but at the same time, some grain-growing areas in the east have seen an increase in the number of frost days. More broadly across the entire wheat belt there has been an increase in the length of the frost season, which means frosts are occurring earlier and later in the year (Figure 2).
“This means that frosts are becoming more likely, and over a wider time-frame. Growers need to consider this when setting up their grain program in terms of how to plan their year to avoid a wipe-out by frost. Completely avoiding frost is not possible but agronomic practices like clay spreading or delving can be considered along with spreading sowing dates and understanding new varieties and their maturation, so that the impact of a single severe frost may be reduced” Ms Rebbeck said.
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