2030 and 2070 pasture predictions for Elliot

Pasture predictions for the Elliot region are based on the assumption that the pasture system is comprised of perennial ryegrass and white clover.

The predictions suggest that:

• Both dryland and irrigated pasture production will increase approximately 8% and 11% respectively by 2030 under the high emission scenario due to warmer winter temperatures and increased CO₂ availability to plants.
• By 2070 both dryland and irrigated pastures are slightly reduced because of warmer late spring and summer temperatures.
• Drainage is reduced in these pasture systems with a 5% increase in irrigation requirements in the 2030 and 2070 High scenarios compared to the baseline.

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 Tasmania. 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 the Elliot region, the average dryland pasture production yield in terms of tonnes of dry matter per hectare (t DM/ha) is predicted to increase by approximately 10% for perennial ryegrass/white clover pastures by 2070, and 8% by 2030. Irrigated pasture production is predicted to increase by approximately 11% and 10% by 2070 and 2030, respectively but this assumes that the increased irrigation water requirement is available.

Drainage is reduced in these pasture systems with a 5% increase in irrigation requirements in the 2030 and 2070 High scenarios compared to the baseline.

The following graphs show box-plots of predicted annual pasture production for dryland and irrigated pastures for Elliot 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 figures below show rainfall, runoff and drainage at Elliot under dryland conditions and include irrigation requirements for irrigated conditions. The data are presented for baseline (1971-2000), and the predictions by 2030 and 2070 under the high emissions scenario. As shown, drainage is reduced by both 2030 and 2070 for both dryland and irrigated conditions, with a slight increase in irrigation demand by 2070.

(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.)