For the Wagga Wagga region, the average pasture production yield in terms of tonnes of Dry Matter per Hectare (t DM/ha) is predicted to increase under low level climate change by up to 12%, although higher levels of climate change predict substantial declines of up to 17% by 2070. This is largely because winter growth rates will be stimulated by increased availability of CO2 to plants, but the shortening of the spring growing season led to overall production decline. There is little effect predicted of increased rainfall variability on annual pasture production by both 2030 and 2070 for Wagga Wagga.
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 southern 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.
The following graphs shows box-plots of predicted mean monthly pasture production for dryland pastures for Wagga 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 following figure depicts the water balance of rainfall, runoff and drainage at Wagga Wagga for baseline (1971-2000) and 2030 and 2070 under the high emissions scenario. Importantly this graph shows a reduction in rainfall and drainage that (as shown in the above box plots) will adversely affect pasture production, despite the anticipated warmer winter periods and increased CO2 available to plants.
(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.)