Predicted climate change impacts on northern NSW farming systems

Take home messages

An increasing body of scientific evidence regarding the impact of human activity on the earth’s climate has shifted the debate from “Is climate change real?” to “What can we do about it?”  Adapting current management activities must include considerations of both climate variability and change.  Advisers have a vital role in helping to develop information-rich farming systems that will improve responses to current climate variability and that can enhance adaptation to climate changes.

Historical changes in climate?

Globally averaged air temperatures have warmed by over 1^oC since records began in 1850, and each of the last four decades has been warmer than the previous one (IPCC 2018).  This warming is driven by increasing concentrations of all the major long-lived greenhouse gases in the atmosphere, with carbon dioxide (CO₂) concentrations rising above 400 ppm and the CO₂ equivalent (CO₂-e) of all gases reaching 500 ppm for the first time in at least 800,000 years (Foster et al., 2017).

In Australia, warming in average temperatures since 1910 has exceeded 1^oC (BoM and CSIRO 2018). The frequency of both day-time and night-time temperature extremes have also changed. High monthly maximum temperatures that occurred around 2% of the time in the past (1951–1980) now occur around 12% of the time (2003–2017) (BoM and CSIRO 2018). Similarly, the frequency of very warm monthly minimum, or night-time, temperatures has changed from 2 to 12% more recently. This shift in the distributions towards hotter temperatures and more extreme high temperature conditions has occurred across all seasons, with the largest change being in spring (BoM and CSIRO 2018).

In Walgett, over the period 1950 to 2018, warming has occurred in maximum temperatures of approximately 1.22^oC. A declining trend in annual rainfall has also been observed, with around 23% less annual rainfall now than in 1950. Evaporation rates have also risen, driven by warmer maximum temperatures with an additional 240 mm occurring now than in 1950. When comparing the proportion of evaporation to rainfall, the local warming has resulted 29% higher water deficit than in 1950.

We can compare the distribution of annual mean maximum and minimum temperatures for the period 1950 to 1984 and 1985 to 2019 (Figure 1 and Table 1).  The analysis reveals that the warming that has occurred has increased the frequency of annual mean maximum temperatures of 29^oC from 6% to 20% (Figure 1 and Table 1).  The distributional changes in annual mean minimum temperatures are more complex, with a decline in the frequency of warmer temperatures i.e. above 14^oC but an increase in the frequency of temperatures between 13 and 14^oC.

A similar examination of maximum and minimum temperature extremes (Figure 2 and Table 1) shows that despite some warming in mean minimum temperatures, the frequency of cold extremes has increased i.e. minimum temperatures of -4^oC have increased in frequency for 2% to 13% (Figure 2).

The increase in extreme hot days has clearly increased with temperatures of 48 to 50^oC now twice as frequent as in the earlier record (Figure 2)

Figure 1. Probability distributions of mean annual minimum temperature (left) and mean annual maximum temperatures (right) for Walgett for two periods,  1950 to 1984 and 1985 to 2019.

Figure 2. Probability distributions of annual minimum temperature (left) and annual maximum temperature (right) extremes for Walgett for two periods,  1950 to 1984 and 1985 to 2019.

Since 1950 Walgett has experienced historical declines in winter and spring rainfall, with slight increases in summer rainfall.  The distribution of annual rainfall for the period 1985 to 2019 shows a higher frequency of amounts between 100mm and 200mm and lower frequency of amounts greater than 700mm (Figure 3 and Table 1). Reduction in rainfall over the observed record has resulted in later season breaks (now +/- 14 days later) and longer dry spell lengths (JJA and SON).

Figure 3. Probability distributions of annual rainfall for Walgett for two periods,
1950 to 1984 and 1985 to 2019.

Table 1. Observed changes in maximum, minimum temperature and rainfall for the period 1950 to 1984 and 1985 to 2019.  
Data is sourced from the Australian Bureau of Meteorology.

The current acceleration of global warming is expected to continue based on future greenhouse gas (GHG) emissions trajectories. Previous studies have examined how the rates of record-breaking have changed in the US (Anderson & Kostinski 2011), the UK (Kendon, 2014), and Australia (Lewis & King, 2015). These studies have found increased rates of hot temperature records and decreased record setting for cold temperatures in recent decades (King et al., 2015; King, 2017). Lewis and King (2015) found that from 2000 to 2014 there were 12 times as many hot record‐breaking temperatures as cold records in Australia and attributed this to anthropogenic climate change. Across the world, there were about five times more record‐breaking monthly temperatures than would be expected without human induced climate change (Coumou et al., 2013) over the early 21st century.

Climate change has been found to not only increase the likelihood of breaking high temperature records (e.g. Lewis and Karoly, 2013), but record‐breaking hot summers and years over previous decades are also attributable to anthropogenic climate change (King et al., 2016). More recent research by Mann et al. (2018) has shown that the synoptic features (large scale weather systems) responsible for prolonged heatwaves are on average 50% more prevalent by 2050 under a business-as-usual GHG emissions trajectory.

In addition to record breaking temperatures, changes in rainfall patterns, sea levels, rates of glacial retreat and biological responses have also been detected consistent with expected climate change projections.  This mounting evidence has led to scientific consensus that:

Emissions of greenhouse gases and aerosols due to human activities continue to alter the atmosphere in ways that affect the climate system and these changes and resultant trends will continue for the foreseeable future; and

There is at least 95% confidence that humans are the main cause of global warming since 1950, and most likely responsible for 100% of that temperature rise (IPCC, 2013) with a less than 1 in 100 000 chance that human activities are not responsible for the observed increase in global temperatures (Kokic et al., 2014).

These changes are already likely to have negatively impacted on Australian agriculture, acting as a major drag on yield growth (Hughes et al., 2017) with similar impacts on yield growth globally for the major crops (Porter et al., 2014).

A major issue in understanding historical and future climate change is how much are the various human-induced climate forcings (greenhouse gas emissions, stratospheric ozone depletion, Asian aerosols, and landcover change) interact with components of natural variability (Watkins 2005, McKeon 2006). Thus, it is important for successful climate adaptation that agricultural decision-makers keep informed of the evolving climate science and updated climate change scenarios.  As scientific understanding improves and there is more confidence in emission scenarios, current and future uncertainties can be rapidly assessed in terms of decision making.

What is expected to happen in the future?

In response to the continued growth in atmospheric GHG concentrations, scientists estimate that global average temperatures could increase by up to 4.8^oC by the end of the present century, dependent on global population growth, technological advancement and economic growth (IPCC, 2013). To put this in context, the difference between our historical temperatures and those of the last ice age was only about 5^oC. So even though 4.8^oC does not sound like much, it signals a huge change in how the climate-ocean-land systems of the earth function and hence how agriculture will operate.

In Australia, national projections suggest up to 1.3^oC of additional warming could be experienced by 2030 and up to 5.1^oC of warming could be experienced by 2090, with the greatest warming being in inland Australia and the lesser warming along the southern coast and Tasmania (CSIRO, 2015). Global studies indicate that a rule of thumb is that global potential crop production drops by 6% per degree warming (Porter et al., 2014).

Whilst changes in rainfall are more uncertain, projections suggest drier conditions in the southern half of Australia, particularly in the south-west and during the cool season months of May to October, with as much as 20% less by 2030 and up to 50% less rainfall by 2090 (CSIRO, 2015).

At a regional scale projected change in climate for the Far Western region (Walgett represents an eastern town in this study region) are summarised in Table 2.  Estimates of median annual warming for 2030 are 0.7^oC and for 2070 are 2.1^oC (Table 2).  Projected changes in annual rainfall for 2030 are small (i.e. +1%) due to projected increases in autumn and summer (i.e. +14% and +3% respectively) and decreases in winter (-7%) and spring (-10%).  By 2070 projected median increases in annual rainfall are +8%, driven by projected mean increases in all seasons except spring (Table 2). Due to continued warming, evaporation rates are likely to increase.  The annual potential evaporation (1986-2005) for the region is 2121 mm. By 2030 the median value of annual potential evaporation is projected to increase by 8% and by 2070 by 17%.

Table 2. Projected changes in temperature and rainfall for the Far West region (Walgett is on found on the eastern part of this region).  Present average temperatures and rainfall are calculated for the period 1986 to 2005.  The data contained in this table represents information compiled from the Queensland Department of Environment and Science, SILO database and NARCliM databases.

To contextualise the projected changes discussed above, we can identify locations in Australia where its current climate is similar to the projected climate for Walgett in 2030.  These locations are sometimes referred to as climate analogues and include Dirranbandi, Roma, Bourke, Augathella, Brewarrina, Tambo, Collarenebri, Cunnamulla, Mitchell, Charleville, St George and Lightning Ridge (Figure 4).

Figure 4. Present day geographical analogues that reflect what Walgett’s climate could be like in 2030. Data sourced from https://www.climatechangeinaustralia.gov.au/en/climate-projections/climate-analogues/analogues-explorer/

The impacts of climate change on wheat production for Walgett have been simulated using the Agricultural Production Simulator (APSIM).  The simulations are based on a continuous wheat rotation with a Sunvale wheat variety, grown on a grey vertosol soil. The simulations were run using daily climate data for the period 1990 to 2018, with future scenarios for 2030 and 2070 produced by scaling daily temperature and rainfall from the historical baseline period by the mean annual values found in table 2.

If the 1990 to 2018 climate were to change, with a mean increase in temperature of 0.7^oC and slight increase of 1% in annual rainfall (i.e. the median 2030 projection), small improvements (approximately 80 to 200 kg per hectare) might be possible for 5^th and 25^th percentile yields (Figure 5).  The 75^th percentile yields are likely to decline by 200 kg per hectare, with little change in the 95^th percentile yields (Figure 5).

If temperatures were to increase by 2.1^oC and annual rainfall where to increase by 8% from the 1990 to 2018 base period, further improvements in the 5^th and 25^th percentile yields are possible (i.e. 500 kg per hectare) (Figure 5).

This simple example highlights the sensitivity of wheat production at Walgett to temperature increases and modest changes in annual rainfall, but does not take into consideration the compounding effects pest and disease. This simulation exercise does begin to make a case for adaptation at a range of spatial scales including farm-level and regional scales as well as changes to strategic planning and polices at the state and national level.

Figure 5. Boxplots of wheat yield for Walgett for the period 1990 to 2018 (baseline), for a 28 year period centred on 2030 and 2070. Simulations were undertaken using APSIM based on a continuous wheat rotation with the Sunvale wheat variety on a grey vertosol soil. Yields are expressed in kilograms per hectare. The horizontal line indicates the average yield, the top and bottom of the ‘box’ indicates the 25^th and 75^th percentiles (i.e. the yields exceeded in 3/4 and 1/4 of years) and the tops and bottoms of the ‘whiskers’ indicate the 95^th percentile and bottom 5^th percentile values).  Climate scenarios for the 2030, 2050 and 2070 simulations are based on the mean annual projections of change in temperature and rainfall found in Table 1.

Adapting to projected climate changes

Climate change is likely to pose a significant challenge for Australian agriculture. Of greatest concern are likely to be changes in water availability, and the change in frequency of climatic extremes (e.g. heatwaves, drought and floods).

Many of the actions required for adapting to climate change are extensions of those currently used for managing climate variability.  For this reason, efforts to improve current levels of adaptation to climate variability will have positive benefits in addressing likely climate change impacts.

Examples of likely farm level adaptation options include:

• Enhancing the current implementation of zero tillage and other minimum disturbance techniques, retaining crop residues, extending fallows, changing row spacing, changing planting density, staggering planting times, traffic and erosion controls
• Alter planting decisions to be more opportunistic – more effectively considering environmental condition (e.g. soil moisture), climate (e.g. seasonal climate forecasting) and market conditions
• Expand routine record keeping of weather, production, degradation, pest and diseases, weed invasion
• Incorporating seasonal climate forecasts and climate change into farm enterprise plans
• Improve efficiency of water distribution systems (to reduce leakage and evaporation), irrigation practices and moisture monitoring
• Learning from farmers in currently more marginal areas
• Selection of varieties with appropriate thermal time and vernalisation requirements, heat shock resistance, drought tolerance, high protein levels, resistance to new pests and diseases and perhaps that set flowers in hot/windy conditions
• Enhance current consideration of decision support tools/training to access/interpret climate data and analyse alternative management options (e.g. APSIM, EverCrop).

There are also longer-term decisions at a family farm level - to sell up, to buy more land, where to invest. These are especially pertinent for farmers in low rainfall regions and it will increasingly be more difficult to find no-regret decisions if climate change progresses as anticipated (Hayman 2005). These decisions, along with industry infrastructure (silos etc.) and industry support (drought policy), are hard decisions requiring full understanding of the likely future risks (Hayman 2005).

The value of adaptation

There is a growing international body of research examining the benefits of adaptation to climate variability and change, showing a number of adaptation options are available to reduce the possible impacts of climate change.

In Australia studies have examined the economic benefits of adaptation in the wheat industry at both national and regional scales under a range of likely future climate conditions. Hochman et al. (2017) highlighted that the adoption of new technology and management systems has held actual yields fairly steady: without these advances, water-limited yield would have dropped by 27%. It was estimated that rainfall declines should have accounted for about three-quarters of the fall in simulated yield potential, whilst observed warming should have accounted for about a quarter of fall in yield potential.

Continued adaptation to climate change has been estimated to add an additional AU$500 M per annum to Australia’s annual income from wheat exports (Howden and Crimp 2011) via the introduction of improved water-use efficiency options and may mitigate potential yield losses by up to 18% through broader scale adaptation (Ghahramani et al. 2015).

The results suggest a number of adaptation options exist to manage increased future downside risk, however the effectiveness of adaptation is driven by the extent of future change. Under conditions of large climate change, tactical adaptation will only have limited effectiveness. More extensive adaptation options, often defined as transformation adaptation, may be required.

Advisers have a key role to play in changing the nature of the climate change dialogue. In the space of about five years, many grain growers and their advisers have moved from asking "What is climate change?" or "Is it real?" to "How do we manage for climate change?" and "What will the impact be on the grains industry?"

Advisers have a vital role to play in this dialogue, not only in assisting grain growers in reducing greenhouse gas emissions from on-farm activities, but also in developing information systems that growers can tap into in order to build farming systems that can cope with current climate variability and can adjust to ongoing climate changes.

References

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Acknowledgements

The authors would also like to acknowledge that this research was made possible via financial support from the New South Wales Department of Environment and Heritage. We would like to acknowledge the Australian Bureau of Meteorology (BoM) for provision of its Australian Climate Observations Reference Network – Surface Air Temperature (ACORN-SAT) data and the Science Division of the Queensland Department of Environment and Science (DES) for provision of it SILO climate data. The authors would also like to acknowledge the projection data sets sourced from NARCliM and the climate analogue data from the CSIRO climate projections website.

Contact details

Dr. Steve Crimp
Climate Change Institute
Australian National University
Fenner School of Environment and Society
Building 141, Linnaeus Way, Action, ACT 2601
Ph: 02 6125 7265
Email: Steven.Crimp@anu.edu.au