Climate change in the Corrigin 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 a decrease in rainfall and an increase in temperature occurred 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 to WA’s economy each year. Corrigin is 230 kilometres south-east of Perth in the central grainbelt. This agri-climate profile provides a historical analysis and future projections for a range of climate variables relevant to farm businesses in the Corrigin area.

Changes at a glance

The observed trends in Corrigin’s climate include:

• a decline in annual rainfall
• a decline in growing season rainfall
• fewer very wet years
• fewer rain days in winter
• an increased risk of consecutive drought years
• more heavy rainfalls in summer
• more variable and later starts to the growing season
• an increase in autumn maximum temperatures
• an increase in the number of frosts in winter.

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What the records show

There were observed shifts in climate for Corrigin 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 has decreased by 5% from 1931–1974 to 2000–2018.
• Growing season rainfall (April–October) has declined by 12% since the mid-1970s, with a further 12% decline since 2000 (Figure 1).
• The chance of 2 consecutive drought years (decile 3 growing season rainfall or below) has increased from 5% in 1931–1974 to 14% in 2000–2018.

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

Around the mid-1970s, there was a shift to consistently drier winter conditions. Figure 2 shows a significant decline in May and June rainfall from 1931–1974 to 2000–2018. Because of the high variability between years, the change in average monthly summer rainfall was not significant between 1931–1974 and 2000–2018.

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

Figures 3 and 4 show that the reduction in winter rainfall was a combination of fewer days with heavy rainfalls, fewer days with rain and less rain during a rainfall. 

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

Figure 4 Average number of rain days per month for Corrigin 1931–2018

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Temperature

Since the mid-1970s, mean monthly maximum temperatures significantly increased in April, May and July (Figure 5). Average monthly minimum temperatures significantly increased in February, April, May and November (Figure 6).

Figure 5 Mean maximum monthly temperature for Corrigin for 1931–2018

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

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

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

The number of frost days (minimum temperature below 2˚C) significantly increased in June. The average date of last frost was 1 October in 1939–1974 and 3 October in 1975–2010. Therefore, frost risk around flowering is still present (Figure 8).

Figure 8 Average number of days below 2°C for Corrigin 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 more rainfall in summer (Figure 9).

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

Temperature

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

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

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What are the agronomic implications?

• Declining growing season rainfall led to a start to the season that is 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 22 May for  1931–1974, to 26 May for 1975–2010, and 29 May for 2000–2018.

Figure 11 Break of the season for Corrigin for the years 1931–2018

• A later and more variable start to the growing season increases production risk for crops and pastures. Declining autumn rainfall means crops needs to be established at the earliest opportunity. Storage and 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 a large reduction in 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 lighter rainfalls mean that evaporation losses are more significant and less water is stored deep in the soil. The greatest risks are increased moisture stress when crops are establishing and finishing.
• Declining growing season 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 remains a significant risk in winter.

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 soil and water resources:

• broadacre cropping
• broadacre livestock production
• horticulture
• pastoral industry
• soil and water resources.