Pasture predictions for the Kyogle region are based on the assumption that the pasture system is comprised of Kikuyu with annual ryegrasses sown in autumn. The predictions suggest that overall water balance will be minimally affected and pasture growth may increase by approximately 5% by 2030. This gain is reduced to less than 1% pasture growth by 2070 under the high emissions scenario mainly because of hotter summer temperatures offsetting warmer winters and more CO2 available to plants. These conditions suggest C4 species may tend to dominate pasture systems, leading to a slight but overall decline in pasture quality.
The following graph shows predicted pasture growth under three possible scenarios of:
Currently, emissions are tracking the high global emissions scenario and therefore, it is the most relevant for northern NSW. One can assume that something like this high scenario will occur in the absence of major global emission reductions.
The following graphs are expressed as ‘box plots’, which need some explaining in order to be easily understood. The box plot is interpreted as follows:
It is important to note that the predictions are not attempting to describe exactly what will actually happen in the specific year of 2030 or 2070, but indicate a the range pasture production conditions that might be expected at that time in the future, based on the current climate change scenarios.
For the Kyogle region, the average pasture production yield in terms of tonnes of Dry Matter per Hectare (t DM/ha) is predicted to be negligible for kikuyu/annual ryegrass pastures by 2070, although up to almost 5% increase in the seasonal pasture growth pattern is predicted by 2030 under the higher the emissions scenario.
The 2070 predictions show an increase in spring growth due to an earlier finish to annual ryegrass and the start of kikuyu growth, although this is offset across the whole year. There is little effect predicted of increased rainfall variability on annual pasture production by both 2030 and 2070 for Kyogle.
The following graphs shows box-plots of predicted mean annual pasture production for dryland pastures for Kyogle by 2030 and 2070. The far left plot is the baseline or current situation, while the second, third and fourth plots show predicted pasture yields under low, medium and high climate change scenarios.
The below figure shows rainfall, runoff and drainage at Kyogle for the baseline (1971-2000) and predictions for 2030 and 2070 under the high emissions scenario. As shown, no major changes are predicted for Kyogle.
(Hotlink to report: Eckard R, Cullen B, 2008 WFSAT Phase II – Final Report: Whole Farms Systems Analysis and Tools for the Australian and New Zealand Grazing Industries, published by MLA, DA, AgResearch Limited, December.)