Future Ready Dairy Systems

Dairy Australia

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2030 and 2070 Pasture Predictions for Kyabram

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 high emission scenario for 2030 predicts increases of about 12% in annual production of irrigated perennial ryegrass, sub-clover and paspalum pastures. This is because increased summer production, due to earlier growth of paspalum and higher summer growth rates, more than compensate for declining perennial ryegrass production in spring.
  • However, under the 2070 high scenario annual pasture production increases by only approximately 1%.
  • Average irrigation water requirements increased by 35-47 mm under the 2030 High scenario and approximately 58-70 mm/year under the 2070 High scenario compared to the baseline scenario, without changing the length of the irrigation.
  • Rainfall variability treatments had little effect on pasture production because the model assumes that irrigation water is available.

The following graph shows predicted pasture growth under three possible scenarios of:

  • low global emissions scenario
    This scenario is based on a coordinated world response to climate change that results in rapid reductions in greenhouse gas production leading to only very small changes in the climate by 2030;
  • medium global emissions scenario
    This scenario is based on future global emissions being balanced across a range of renewable and non-renewable energy sources resulting in mid-level emissions and medium level climate change by 2030.
  • high global emissions scenario
    This scenario is based on relatively unconstrained growth in global emissions using mostly non-renewable energy sources that results in higher levels of climate change by 2030.

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:

  • Each box plot represents 30 annual simulation, in order to get some idea of the variation around the average for the baseline (actual 1971 to 2000 data, and the 2030 and 2070 scenarios)
  • The box itself contains the middle 50% of the data. The upper edge of the box indicates the 75th percentile of the data set, and the lower hinge indicates the 25th percentile.
  • The line in the box indicates the median value of the data.
  • The ends of the vertical lines or “whiskers” the 10 percentile (lower) and 90 percentile (upper).
  • The points outside the ends of the whiskers are the two highest and two lowest estimates from the 30 annual simulations.

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.)