Climate change in the Cunderdin area, Western Australia

Why this information is important

Climate change and climate variability have already challenged Western Australian (WA) broadacre cropping and animal production. Producers have been able to meet these challenges by adopting innovative farming systems to maintain farm productivity and profitability. Future climate change will present further opportunities and challenges for producers.

Records show that rainfall decreased and temperature increased over the last century. Climate projections for the south-west of WA are for declining rainfall and higher temperatures.

The grainbelt of WA contributes more than $4.5 billion a year to WA’s economy. Cunderdin is 150 kilometres east of Perth in the middle of the central grainbelt. This agri-climate profile provides an analysis of records and projections for a range of climate variables relevant to farm businesses in the Cunderdin area.

Changes at a glance

The observed trends in Cunderdin’s climate include:

• a decline in annual rainfall
• a decline in growing season rainfall
• an increased chance of consecutive drought years
• more drier than usual years
• a decline in the number of heavy rainfalls and number of rain days in winter
• an increase in the number of heavy rainfalls in summer
• more variable and later starts to the growing season
• increased average maximum temperatures 
• an increased number of frosts around flowering.

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What the records show

There were shifts in climate for Cunderdin in the mid-1970s, then again around 2000. Therefore, the analysis is for 1931–1974 (43 years), 1975–2018 (43 years) and 2000–2018 (18 years).

Rainfall

• Total annual rainfall decreased by 8% from 1931–1974 to 1975–2018.
• Growing season rainfall (April–October) declined by 12% from 1931–1974 to 1975–2018, with a further 15% decline since 2000 (Figure 1).
• The chance of two consecutive drought years (decile 3 growing season rainfall or below) increased from 5% in 1931–1974 to 14% in 1975–2018.

[1]

Figure 1 April to October rainfall for Cunderdin for the years 1931–2018

Around the mid-1970s there was a shift to consistently drier winter conditions. Figure 2 shows a significant decrease in May and June rainfall between 1931–1974 and 1975–2018.

[2]

Figure 2 Monthly average rainfall for Cunderdin for the years 1931–2018

Figures 3 and 4 show the decline in June rainfall was caused by a combination of fewer days with heavy rainfalls (greater than 5 mm) and fewer rain days.

[3]

Figure 3 Average monthly number of rainfall events greater than 5mm for Cunderdin 1931–2018

[4]

Figure 4 Average monthly number of rainfall days for Cunderdin 1931–2018

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Temperature

Since the mid-1970s, mean monthly maximum temperatures significantly increased in April, May, October and November (Figure 5). Average monthly minimum temperatures remained unchanged, except for a significant decrease in June (Figure 6).

[5]

Figure 5 Average monthly number of rainfall days for Cunderdin 1931–2018

[6]

Figure 6 Mean minimum monthly average temperatures for Cunderdin 1931–2018

The number of days with maximum temperature above 35 degrees Celsius (˚C) remained about the same (Figure 7).

[7]

Figure 7 Average number of days over 35°C in Cunderdin for 1931–2018

The number of frost days (minimum temperature below 2˚C) significantly increased in July, September and October. Frost risk around flowering significantly increased (Figure 8). The average date of last frost was 31 August in 1931–1974 and 14 September in 1975–2018.

[8]

Figure 8 Average number of days below 2°C for Cunderdin for 1931–2018

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Projected changes

The following projections for 2035–2064 were obtained using an intermediate emissions scenario (A2) and downscaled data from the CSIRO Global Climate Model CCAM (CMIP3).

Rainfall

Projections are for less rainfall in autumn–winter and spring (Figure 9).

[9]

Figure 9 Historical monthly rainfall for 1939–1974 and 1975–2010 and monthly projected rainfall for 2035–2064

Temperature

Projections are for increasing average monthly maximum temperatures (Figure 10).

[10]

Figure 10 Historical mean monthly maximum temperature for 1939–1974 and 1975–2010 and projections for 2035–2064

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What are the agronomic implications?

• Declining growing season rainfall led to the start of the growing season being more variable and generally later (Figure 11). The average start of the growing season, derived from a sowing rule that uses a sowing window starting from 25 April, has shifted from 20 May for 1931–1974, to 27 May for 1975–2018 and 2000–2018.

[11]

Figure 11 Break of the season for Cunderdin for 1931–2018

• Later and more variable starts to the growing season will increase production risk for crops and pastures. Declining autumn rainfall means that crops needs to be established at the earliest opportunity, possibly with dry seeding. Conservation of out-of-season rain is gaining importance. Effective control of summer weeds and stubble is becoming more important.
• The loss of heavy rainfalls in winter has led to reduced reliability of run-off into farm dams. Roaded and natural catchments will need to be 15–20% larger to fill existing dams.
• Declining growing season rainfall and the occurrence of lighter rainfalls has led to greater proportional evaporation losses and less water stored deep in the soil. This increases the risk of moisture stress during crop establishment, flowering and grain filling.
• Declining winter rainfall will reduce annual pasture production. Flexible lot-feeding or confined feeding systems may need to be established to maintain or finish livestock in dry years.
• Frost risk in winter and spring has increased significantly and is likely to remain at this level.

What are the options for adapting to climate change?

We provide information and technical support for making changes at the incremental, transitional and transformative levels. A general guide is available for each major enterprise and for resource management:

• broadacre cropping [12]
• broadacre livestock production [13]
• horticulture [14]
• pastoral industry [15]
• soil and water resources [16]