The Impact of Climate Change on Crop Diversity in South Australian Farms

Most climate change impacts on agriculture focus on farm-scale outcomes (e.g., changes in profit) as profits are what drives farmer adaptation responses. Australian broadacre farms typically combine cropping and livestock activities.

A variety of modelling techniques estimate agricultural climate change impacts each with their own strengths and weaknesses. This paper uses a statistical model to estimate climate change impacts on agricultural production.

1. Drought

Drought is a significant challenge for all farmers, but for those growing crops it presents the most significant threat to profitability. Various drought indicators have been developed to support government policy and private drought insurance markets, but none capture the more subjective aspects of farmer perception of conditions (see Botterill 2003).

While it is difficult to distinguish human influences from natural variability, research has detected some signals of change in the climate system. In particular, a decrease in winter rainfall that is large compared with historical natural variation has emerged in the southern Australia cropping region. This trend is likely to be caused by a weakening of the Walker Circulation associated with the El Nio–Southern Oscillation, and could result in increased dry states compared to past decades (CSIRO 2010).

Rainfall predictions have less confidence than temperature projections, but global climate models generally agree that reduced rainfall will occur across south-eastern Australia, especially in autumn and winter. This is expected to lead to lower agricultural production and water availability (Cai & Cowan 2013; Van Dijk et al. 2013).

Despite the uncertainty in predicting the frequency of drought, it is clear that farmers’ perceptions of drought are shifting. The proportion of AAGIS farms that self-assessed as ‘in drought’ has decreased over time, although this varies by state. For example, in NSW and QLD, farmers reported being in drought around 30% of the time between 1992-93 and 2018-19, whereas this was only about 12% for farms in SA and VIC.

It is likely that the shift in drought perceptions reflects farmers’ adaptation to a changing climate. For example, they may be adapting to a reduced supply of water by reducing irrigation use, or they might be adjusting their cultivation techniques to increase the potential yield from available water.

2. Flood

A warming planet is expected to increase the frequency of extreme rainfall events, which can lead to floods and erosion. These will likely reduce crop yields, and may damage infrastructure such as roads, railway lines and irrigation dams. They may also result in polluted or depleted water supplies, which will impact drinking and other water-dependent industries (CSIRO 2011).

Climate change is accelerating the onset of summer heat waves, increasing the intensity of droughts, and altering rainfall patterns. These changes will affect crop, livestock and land management strategies on a national scale. However, the specific impacts will vary among farmers, as a result of differences in their current cultivation practices and the types of crops they grow.

Farming communities are particularly vulnerable to the escalating effects of global climate change, as their agricultural production is dependent on weather conditions. Failing crops and livestock will lead to increased dependence on government support programs, while deteriorating local water supplies can cause economic hardship for the entire community.

The research in the Mallee & Wimmera regions found that farmers’ attitudes and behaviours towards climate change are complex and varied. Although most respondents in the survey were sceptical about human causality in climate change, their beliefs did not correlate with their on-farm adaptation decisions. However, it is possible that strength of belief in the phenomenon relates to the level of urgency felt about taking action. This is supported by the finding that householders with a strong place attachment to their local area were more inclined to take risk mitigation actions, including prescribed burning and clearing of native vegetation. These actions reflect their recognition of a relationship between climate change and wildfire risk, which is consistent with findings in other studies, such as those by Wheeler et al. [43] in the Murray-Darling Basin and Blennow et al. [44] in Swedish forest owners.

3. Heat

Increasing average temperatures and higher rates of extreme heat, as well as reduced rainfall and water scarcity, are expected to reduce crop productivity (CSIRO 2011). Crops are also likely to be vulnerable to pests and diseases in future. Human health is predicted to be adversely affected by the spread of mosquito-borne infectious diseases such as dengue fever and malaria, and Ross River virus infection (Doctors for the Environment Australia 2011). Built infrastructure is at risk from damage from bushfire and flooding, and electricity disruptions caused by surges in demand during hot weather.

The South Australian climate has already shifted significantly over recent decades with decreases in autumn and winter rainfall across the state (CSIRO 2010). This is a result of global changes to atmospheric circulation, including an expansion of the subtropical ridge and the resulting change to the Indian Ocean Dipole.

Rainfall patterns are also changing within regions, with decreasing late winter and spring rainfall in some areas, and increased summer and autumn rainfall in others. These changes are expected to continue, although it is not yet clear whether the overall trend will be a reduction or an increase in rainfall over South Australia.

A major finding of the research was that farmers autonomously adapt to risks induced by climate change, based on their environmental values and place attachment. For example, those in group one are more likely to recognise that climate change alters wildfire risk and are supportive of the use of prescribed burning and vegetation clearing to mitigate this threat. However, those in group three are less aware of the impact of climate change on bushfire risk and are more reticent about taking action to reduce this risk.

4. Cold

In South Australia, the prevailing climate is drier than in the past and rainfall is projected to continue decreasing. This is due to global warming, a change in the atmospheric circulation and an expansion of the tropics. This is expected to result in fewer cold fronts and storm systems which are critical for our rain-fed agriculture.

These changes will also increase the temperature gradient between the surface and the atmosphere, meaning that more heat will be trapped at lower altitudes and less cold air will reach higher altitudes. This is expected to have an impact on the availability of freshwater at lower latitudes and on marine ecosystems. For example, there are concerns that increased surface water temperatures will reduce the frequency of upwelling, which brings nutrients from deep ocean waters to the surface and supports the biodiversity in marine ecosystems such as rock lobster, blacklip abalone and King George whiting.

The ABARES research shows that, based on the current climatic conditions, wheat yields are expected to decline over the coming decades in both Mallee and Wimmera. This is partly because of increased exposure to extreme temperatures, but also because of lower winter rainfall, particularly in the Wimmera (Tesfaye et al 2017).

ABARES has used ten climatic projections to assess future crop diversity and farm profits across the state. The projections show that increasing temperatures and decreasing rainfall will significantly reduce wheat yields, while improved soil health and fewer pests will partially offset these effects. It is important that farmers continue to develop new crop varieties, which will improve their ability to cope with climate change and provide high-quality food. These new varieties will also reduce the need for chemical inputs that are expensive, pump carbon dioxide into the atmosphere and are harmful to the environment.

5. Pests

Climate change affects crop diversity through its impact on agronomic characteristics and plant diseases. It also increases the likelihood of a pathogen or pest attack by increasing the degree of uniformity of susceptible traits, the extent of cultivation of the crop and the environmental conditions that favour its multiplication. This effect is heightened when the crop is of high yield potential.

The rate of climate change is faster than in the geological past and will continue to accelerate. Average surface air temperatures on land and in the ocean have already risen by over 0.7 degC since 1910, and will continue to rise (CSIRO 2011).

Increased average temperature leads to shorter growing seasons and more droughts. It also reduces the availability of water to crops because of reduced rainfall and increased evaporation. This reduces crop yields. Climate change will also alter soil nitrogen availability and plant defence mechanisms, which makes them more vulnerable to herbivore insect infestations.

Research has found that agronomic practices can mitigate the impact of climate change on crops. This includes using crop rotations to reduce biotic stress, modified tillage systems for soil conservation and control of weeds, and integrated pest management. These practices can also include the use of cultivars with improved resistance to disease and insect pests.

Interviews with 30 farmers were conducted in two South Australian regions – the Eyre Peninsula and Yorke Peninsula. The number of interviews was limited to avoid data saturation, where no new themes or information are generated during the interview process (Lobell et al. 2015). Interviews were taped and transcribed, and analysed using thematic analysis.