Climate change in the Dalwallinu area, Western Australia

Page last updated: Monday, 16 October 2017 - 3:59pm

The Agriculture and Food Division of the Department of Primary Industries and Regional Development (DPIRD) provides this agri-climate profile of historical and projected climate information to support farm business managers in their response to a changing climate in the Dalwallinu area of Western Australia.

Why this information is important

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

Records show that rainfall decreased and temperatures 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 to WA’s economy per year. Dalwallinu is 220 kilometres north-east of Perth on the eastern edge of the northern grainbelt. This agri-climate profile provides an analysis of records and projections for a range of climate variables relevant to farm businesses in the Dalwallinu area.

Changes at a glance

The observed trends in Dalwallinu’s climate include:

  • little change to annual rainfall
  • a decrease in growing season rainfall (smaller and less frequent rainfalls)
  • a decrease in the number of heavy rainfalls in winter
  • an increase in summer rainfall
  • an increase in the number of heavy rainfalls in summer
  • fewer very wet years
  • more-variable and later break of season
  • an increase in average maximum and minimum temperatures.

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What the records show

There were shifts in climate for Dalwallinu in the mid-1970s, then again around 2000. Therefore the analysis is for 1939–1974 (35 years), 1975–2010 (35 years) and 2000–2010 (10 years).

Rainfall

Total annual rainfall in 1975–2010 decreased by 3%, compared to 1939–1974.

Growing season rainfall (April–October) has declined by 10% since the mid-1970s and a further 15% since 2000 (Figure 1).

The chance of two consecutive drought years (decile 3 growing season rainfall or below) has increased from 5% in 1939–1974 to 14% in 1975–2010.

Bar chart showing variability of rainfall and drop in growing season rainfall since 1974
Figure 1 Time series of growing season (April–October) rainfall (mm). Horizontal lines represent averages for 1939–1974, 1975–2010 and 2000–2010.

Around the mid-1970s there was a shift to consistently drier winter conditions. Figure 2 shows a significant decline in June rainfall and a significant increase in December rainfall in 2000–2010, compared to 1939–1974.

Bar chart showing large decrease of winter rainfall and an increase in summer rainfall
Figure 2 Average monthly rainfall (mm) for 1939–1974, 1975–2010 and 2000–2010

Figures 3, 4 and 5 show the rainfall reduction during June has resulted from a combination of fewer days with heavy rainfall (greater than 5mm), fewer days with any rain and more days with light rainfall. The increase in summer rainfall has mainly resulted from more rain during December and January.

Bar chart showing change in monthly rainfall of more than five millimetres over the three periods
Figure 3 Average number of days with rainfalls greater than 5mm per month for 1939–1974, 1975–2010 and 2000–2010

Bar chart showing the drop in autumn and early winter rain days
Figure 4 Average number of rain days per month for 1939–1974, 1975–2010 and 2000–2010

Bar chart showing very large increase in the average amount of rain in each rainfall in December and January
Figure 5 Average size of rainfalls per month for 1939–1974, 1975–2010 and 2000–2010

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Temperature

Since the mid-1970s, mean monthly maximum temperatures significantly increased during April–July and have remained largely unchanged during the rest of the year (Figure 6).

Bar chart showing a rise in autumn and early winter maximum temperatures
Figure 6 Mean monthly maximum temperature for 1939–1974 and 1975–2010

Average monthly minimum temperatures significantly increased during April, May and November (Figure 7).

Bar chart showing rises in average monthly minimum temperatures
Figure 7 Mean monthly minimum temperature for 1939–1974 and 1975–2010

The number of days with maximum temperature above 35 degrees Celsius (˚C) did not change significantly (Figure 8).

Bar chart showing little change in the number of days each month with days above 35˚C
Figure 8 Average number of days per month with maximum temperature above 35˚C for 1939–1974 and 1975–2010

The number of frost days — days with minimum temperature below 2˚C — significantly decreased during August and remained largely unchanged during September and October. The average date of the last frost was 20 August in 1939–1974 and 13 August in 1975–2010. A frost risk for cereal crops around flowering remains (Figure 9).

Bar chart showing the risk of frost in August has significantly dropped
Figure 9 Average number of days per month with minimum temperature below 2˚C for 1939–1974 and 1975–2010

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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 that rainfall will decrease in autumn-winter and increase in summer (Figure 10).

Bar chart showing a historical and projected decrease in autumn and winter rainfall and an increase in summer rainfall
Figure 10 Historical monthly rainfall for 1939–1974 and 1975–2010 and monthly projected rainfall for 2035–2064

Temperature

Projections are that average monthly maximum temperatures will increase (Figure 11).

Bar chart showing historical and project temperature rises
Figure 11 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?

  • Since 1939, the start of the growing season has been more variable and generally later. The average break of the season, derived from a sowing rule that uses a sowing window starting from 25 April, shifted from 24 May for 1939–1974 to 27 May for 1975–2010. In 2000–2010 the average break was 3 June.

Chart showing how the average break of season is nearly ten days later that before 1975
Figure 12 Time series of date of break of the season. Horizontal lines show averages for 1939–1974, 1975–2010 and 2000–2010.
  • Later and more variable break of season will increase production risk for crops and pastures. Declining autumn rainfall means crops need 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 decline of heavy rainfall events in winter has reduced the reliability of run-off into farm 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 estanlishment, flowering and grain fill.
  • Declining winter rainfall will reduce pasture production. Flexible lot-feeding or confined-feeding systems may need to be established to maintain or finish stock in dry years. Perennial pastures and native pastures should be investigated as a possible alternative to annual pastures.

What are the options for adapting to climate change?

Agriculture and Food provides 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:

Contact information

Rob Sudmeyer
+61 (0)8 9083 1129