Frost risk on the rise despite warmer climate

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An increase in the number of frosts later in the season means more growers are reassessing sowing dates and varieties

Photo of wheat being held

Frost damage.

PHOTO: GRDC

 

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.”

Return on frost research investment

A new two-year research project will quantify the severity, timing and frequency of frost events in different agro-economic zones across Australia. The University of Queensland's Queensland Alliance for Agriculture and Food Innovation (QAAFI) project leader Dr Jack Christopher says the ultimate goal of the new project is to quantify the direct and indirect yield losses associated with frost across each of the GRDC growing regions to better inform research investment.

"Frost causes direct and indirect yield losses," Dr Christopher explains. "We want to quantify these for each region to guide research investments chasing frost avoidance versus frost tolerance and resistance."

Data collected from nearly 3000 weather stations across Australia will be used to analyse the frequency of frost events in each cropping region.

"We will use the frost damage and climate data collected at research sites in past years to determine the minimum temperature required to produce frost damage in each of the major cropping regions," Dr Christopher says.

The resulting crop damage thresholds will be used to quantify yield reductions due to direct frost damage and these, combined with indirect yield losses from late sowing, will be used to estimate the total economic impact of frost in each region.

By quantifying the economic impact of frost the potential impact of research into improved frost management and genetic frost resistance can be estimated.

"Using this information we can then estimate the likely economic return from a research investment achieving a 1ºC, 2ºC  or 3ºC improvement in genetic frost resistance."

Along with an increased incidence of frosts between August and November there has also been a shift to frost occurring later in the year.

Figure 1: Regions of increasing August to November frosts

 

“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).

Figure showing historic number of frosts in flowering window

Figure 2: Historic number of frosts in flowering window 20 September to 30 October, YitpiPBR logo, Longerenong, Victoria.

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,

steven.crimp@csiro.au;

Dr Jack Christopher,
Queensland Alliance for Agriculture and Food Innovation,
07 4639 8813,

j.christopher@uq.edu.au

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Identifying frost in wheat

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GRDC Project Code MCV00010, UQ00071

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