Pasture predictions for the Kyabram region are based on the assumption that the pasture system is comprised of a combination of perennial and annual irrigated pasture. Drastically reduced water allocations over the past 12 years have seen perennial ryegrass/clover pastures largely replaced by annual ryegrass/clover and winter cereals. Annual summer fodder crops such as Sorghum and Maize, and drought resistant perennials such as lucerne have also increased in popularity in recent years.
The predictions suggest that:
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 Victoria. 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 Kyabram, the average irrigated pasture production yield in terms of tonnes of dry matter per hectare (t DM/ha) is predicted to increase by approximately 12% for perennial ryegrass/sub- clover/paspalum pastures by 2030 under the high emission scenario (and slightly less under lower emission scenarios), but by 2070 the increase in annual production from the baseline year is negligible at approximately 1% under the high emission scenario.
The following graphs show box-plots of predicted annual pasture production for irrigated pastures for Kyabram 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 figure below shows rainfall, irrigation, runoff and drainage at Kyabram. The data are presented for baseline (1971-2000), and the predictions by 2030 and 2070 under the high emissions scenario. As shown, rainfall and drainage are reduced by both 2030 and 2070 while irrigation demand increase.
Irrigated farming systems are significantly more complex to understand and model than rainfed systems because of the mitigating effect of irrigation if water is available, or the multiplying effect of the impact if irrigation water is not available. Therefore, for Kyabram this modelling study specifically combined the predicted increases in irrigation requirement (due to higher temperatures and evapotranspiration) with the predicted decreases in irrigation supply as suggested from CSIRO modelling of the Murray Darling Basin.
Results suggest that if we take a hypothetical dairy farm that during the baseline period (1970 to 2000) had 100ha of irrigated perennial pasture, and 25 ha of dryland/annual pasture, then in 2030 this farm would only be able to irrigate 92ha (with 33ha of dryland pasture) and in 2070, the area of irrigated pasture would be reduced to 71ha. Clearly, these long term average figures are substantially above what has been happening in northern Victoria since 2000 and therefore might be treated as under-estimates of the impact of climate change on irrigated dairy systems.
(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.)