Modelling the sensitivity of agricultural systems to climate change and extreme climatic events

Little is known about the impacts of increased frequencies of extreme climatic events (ECEs) on agricultural landscapes, though such events may be much more detrimental than those of gradual climate change alone. Here we develop an approach for examining the sensitivity of agricultural systems to climatic variability and ECEs on pasture-based dairy farms.

Using a combination of spreadsheet formulae, biophysical and economic tools, we compared two approaches for generating future climate scenarios: a ‘Gradual’ approach, wherein climate projections of changes in monthly average temperature and rainfall were applied without altering the pattern of ECEs, and a ‘Variable’ approach, where monthly change projections were combined with more heatwaves, longer droughts and more extreme rainfall events to generate future scenarios with increased variability.

The sensitivity of each approach was compared by modelling whole-farm system impacts on pasture and milk production, feed intake and profit under ‘Low’ and ‘High’ climate change projections based on the Representative Concentration Pathways with the highest greenhouse emissions in 2080 (RCP8.5) at three sites in southern Australia. ‘Low’ change projections had average warming of 1.6–2.0 °C and rainfall 10–18% higher than the historical climate, while the ‘High’ change scenario had 2.5–3.2 °C of warming and 15–30% reductions in rainfall. Both future climate scenarios applied the same average monthly change in rainfall and temperature relative to historical climates, but the relative frequency of events falling in the tails of the historical climate distribution was increased in the Variable approach. When used to simulate impacts on whole farm systems, the Variable approach translated into lower annual pasture growth and utilisation, and greater variation within and across years. Exposure to more frequent ECEs led to greater reliance on purchased feeds and lower long-term profitability, particularly in the High change scenarios.

We conclude that increased climate variability associated with more frequent ECEs has impacts on agricultural systems over and above those of gradual climate change, which may have two main implications. First, climate change projections following RCP8.5 will progressively depress pasture yields and profitability of pasture-based dairy systems. Second, future modelling of climate change impacts on agricultural systems must adopt methodologies that account for the variability associated with ECEs in projected climate data, since the sensitivity of losses in production and profitability becomes greater with more frequent ECEs, even if gradual long-term changes in climate are accounted for.