Whole Farm Systems Analysis and Tools for the Aust and NZ Grazing Industries

Summary

Climate change projections for Australia forecast increasing temperatures and changes to rainfall patterns. The aim of this work was to quantify the effects of climate change scenarios in 2030 and 2070 on pasture growth, species composition and water balance for a range of sites (cool temperate to subtropical) and pasture types, relative to an historical baseline climate. Six future climate scenarios were developed for each site by combining historical climate data with climate change projections for Low, Medium and High climate change scenarios in 2030 and 2070. The impact of the future climate scenarios on pasture production and water balance were modelled using the SGS Pasture Model and DairyMod. Detailed results for each site are presented. 
In general, climate change impacts on pasture production were predicted to be minor under the 2030 scenarios, associated with temperature increases of up to 1.2oC and rainfall reductions up to 9%. However, under High climate change projections for 2070, with up to 4.4oC warming and 30% annual rainfall declines, increased growth and a shift towards C4 dominance was modelled in mixed C3/C4 swards in summer dominant rainfall regions or where irrigation was applied, while declines up to 19% of annual production of C3 dominant pastures in southern Australia were predicted. In the C3 dominant pastures, the decline in production was moderated by reduced drainage below the root zone, and employing deeper rooted plant systems was an effective means of mitigating some of the impact of lower rainfall. In areas where irrigation was used, the irrigation requirement increased by up to 10% (with no extension of the irrigation season), with the greatest increase in the northern Victorian dairying region. This is also an area where climate change is likely to cause a reduction in irrigation water availability.