Farming on the edge: assessing the impact of historical and future climate change on the mediterranean cropping margins of Australia

The boundary between land suitable for low rainfall grain cropping and the arid interior suitable for extensive grazing has a history in South Australia dating back to Goyder in the 1860s and in Western Australia to Brookman in the 1900s. Historical and future shifts in climatically determined edges of cropping regions focus discussion on how farmers might adapt to a changing climate. We integrate the outputs of climate analysis and crop simulation modelling to explore the limits to crop production at the low rainfall margin of cropping in Western Australia and South Australia. Across 40 locations, growing season (April to October) rainfall over the past two decades was 2-27% drier than the long-term record which corresponded to declines in simulated wheat yields. Increasing CO2 levels, from 296ppm in 1900 to 412ppm in 2020, reduced but didn't eliminate the decline in simulated yield. Climate models indicate that even stronger rainfall declines could be experienced in the future, particularly over the Western Australian cropping regions. We ran APSIM simulations with projected climate data from 8 global climate models GCMs for a subset of 8 representative low rainfall sites across the Western Australian and South Australian cropping region. The 8 GCMs provide a range in projected water limited wheat yields consistent with the range of projected changes in rainfall from different GCMs. We discussed the results with low rainfall farmers and advisers in the regions and provide an overview of their responses to aid our interpretation. Farmers maintained that they were continually adapting to season-to-season variation and to the changing climate. Most farmers felt that their current business model was working, and that climate change hadn't forced them to make drastic changes. There was a belief that improved technologies (e.g., new varieties) and agronomy had served them well in the past and would be able to keep pace with the effects of any climate change. Most of the changes over the last 30 years had been within cropping and grazing enterprises rather than changing enterprises to alternative land uses. The uptake of no-till farming was ranked as the largest change which enabled farmers to make better use of rainfall. Farmers had also changed varieties and adopted new crops. Participants accepted the importance of climate in the success of their cropping enterprises and that the climate was changing. However, there was a strong sense of technical optimism and a refusal to have their future defined by climate alone. Some farmers were concerned that transformation may be driven not directly by climate change, but rather by the policies associated with climate change.