Milking the Weather - June 2011 Edition
Impact of climate variability on pasture production
Dr Brendan Cullen, The University of Melbourne
Record rainfall over much of eastern Australia has seen pastures growing all through the summer in southern Victoria. Have we ever seen a summer and autumn period with as much pasture growth as this year?
Modelling of pasture growth rates at Terang in south west Victoria and Ellinbank in west Gippsland suggests that we haven’t. Based on the climate for the past 50 years (1961-May 2011), summer production for 2010- 2011 at both sites was in the top ten per cent of years, while the autumn of 2011 has been the highest producing on record. This long growing season bucks the trend of what we have seen over the past decade.
The seasonal production of a perennial ryegrass-based pasture at Terang is shown in Figure 1, with similar patterns evident at Ellinbank.
Autumn and spring are the two seasons with the greatest variability in dryland pasture growth rates. The length of the spring growing season, whether it is a ‘short’ or ‘long’ spring, is an important determinant of annual pasture production. In the past decade we have seen a higher frequency of short spring seasons. The spring of 2006 was a notable example.
Autumn is another key time of year when pasture growth rates are highly variable, related to the timing of the autumn break. While the Bureau of Meteorology has reported declining autumn rainfall over much of south eastern Australia during the past 50 years, the pasture growth analysis does not indicate a higher frequency of late autumn breaks in southern Victoria. The timing of rain can be just as important as the total amount.
Climate change projections for the next 20 years suggest a drying trend across Victoria, however the predicted changes are small compared to the annual variability in rainfall. So, managing seasonal variability will continue to be the key for climate risk management.
Figure 1. Seasonal pasture production (t DM/ha) at Terang comparing the long term average with the 2010/11 season.
