Timing of autumn breaks and length of springs in Tasmanian dairy regions under future climate scenarios

The timing of autumn breaks and the length of the spring growing season are considered two times of the year when pasture growth can be most variable. Daily climate data for two dairy regions of Tasmania (Flowerdale and Ringarooma) was accessed from the ‘Climate Futures for Tasmania’ project and used to simulate a perennial ryegrass sward using the biophysical pasture model DairyMod. The mean frequency of early and late autumn breaks and frequency of short and long spring seasons for a baseline period (years 1971 to 2000) and three climate periods (years 2001 to 2030, 2031 to 2060 and 2061 to 2090) was predicted for each region using climate projections from six general circulation models. Comparing the mean change between the baseline period and the future climate period, years 2061 to 2090, the frequency of early autumn breaks was predicted to increase from 27% to 33% for Flowerdale and from 26% to 34% for Ringarooma. The frequency of late autumn breaks was predicted to decline from 31% to 16% for Flowerdale and from 34% to 17% for Ringarooma. The frequency of short springs was predicted to decline from 14% and 16% for Flowerdale and Ringarooma, respectively, to < 1% for both regions. The frequency of long springs was predicted to remain relatively stable at ~ 32% for both regions. The results of this study indicate that for both regions of Tasmanian, earlier autumn breaks and a reduction in the frequency of short springs will result in a more reliable growing season. This paper discusses the implications of these results and possible adaptation options.