CLIMATE DRIVERS IN TASMANIA
In Tasmania, Ridgy controls the pressure pattern, allowing rain-bearing fronts through in winter and blocking them more often in summer.
Sam herds up the cold fronts that sweep across Tassie – bringing cold weather and rainfall events.
Indy herds moisture all the way from the Indian Ocean, bringing drier or wetter winter-springs depending on whether he’s feeling positive or negative. He’s more active in the north.
Enso herds moisture from the Pacific Ocean towards Tasmania’s north and east. bringing less rainfall in an El Nino, and more rainfall during a La Nina.
Eastie scampers along the south-east coast of Australia, can go into action overnight, and his favourite seasons are autumn and winter. He can cause strong winds, heavy rains and lots of rough weather.
FUTURE CLIMATE IN TASMANIA
Tasmania’s climate in the decades ahead will be different from what it was in the past. We can expect changes in: temperature, extreme temperatures, sunshine, humidity, wind speed, rainfall, sea-level rise and storm surge, drought and extreme rainfall, and severe weather.
You may need to modify your farming practices to manage the risks presented by the change in climate.
General threats for agriculture across southern Australia include:
- decline in productivity due to increased drought (longer and more intense) and bushfires
- crop yields benefiting from warmer conditions and higher carbon dioxide levels, but vulnerable to reduced rainfall
- greater exposure of stock and crops to heat-related stress and disease
- earlier ripening and reduced grape quality
- less winter chilling for fruit and nuts
- southern migration of some pests
- potential increase in the distribution and abundance of some exotic weeds
The Climate Futures for Tasmania: Impacts on Agriculture report by the Antarctic Climate and Ecosystems Cooperative Research Centre (ACE CRC), provides farmers, agribusiness and agricultural policy makers with important information about the expected impacts of climate change on the agricultural sector.
Temperature projections for Tasmania are for continued warming over the coming decades. Mean or average temperature in Tasmania has increased by more than 0.5 °C since 1950, with a higher trend in the north-east than in the rest of the state. The increase has been greater for minimum temperatures (usually occurring overnight) than for maximum temperatures.
The projection under a low greenhouse gas emission scenario (best case) is for an 0.6°C increase over 1990 climate by 2030, and a 1.0°C increase under a high greenhouse gas emission scenario (worst case). By 2070, under a low greenhouse gas emission scenario (best case), projection is for a 1.5°C increase over 1990 climate, and under a high greenhouse gas emission scenario (worst case), a 2.5°C increase is projected.
The projected rise in mean temperature is relatively uniform across Tasmania. Projected warming for spring and autumn is similar to the annual increase, but slightly greater for summer and slightly less for winter.
Scientists have more confidence in the projections for mean temperature than in those for rainfall. They have more confidence in the projections for 2030 than in those for 2070.
We can expect more very hot days and nights. The largest increases in extreme temperature are projected to occur in the spring and autumn months, with increases of greater than 4°C.
The number of heatwaves (where maximum temperatures exceed 28°C for more than 3 consecutive days) at Launceston, for example, is projected to increase progressively over the coming decades to twice per year, on average. This is approximately 4 times more frequent than what we currently experience. We can expect less frosts and less very cold days and nights.
Relative humidity is likely to increase around Tasmania’s coast, and decrease over inland and high-altitude regions.
Modest increases in wind speed are likely under a high carbon emission–scenario.
Tasmania has experienced a downward trend in rainfall over the period 1970–2011. We have observed the largest changes in autumn. Projections show an increase in rainfall over Tasmania’s coastal regions, and reduced rainfall over central Tasmania and in the north-west.
The projection is for a 2-5% decrease in annual rainfall in 2030 relative to the 1990 climate. Under a low greenhouse gas emission scenario (best case), projection is for a 2-5% decrease in annual rainfall by 2070 when compared to 1990, and under a high greenhouse gas emission scenario (worst case), a 2-10% decrease is projected.
Scientists have more confidence in the projections for temperature than in those for rainfall. They have more confidence in the projections for 2030 than in those for 2070.
Predicted changes in sea levels vary regionally. Projections estimate a sea-level rise of 26–59 centimetres by 2100 for a no-mitigation scenario (IPCC Third and Fourth Assessment Report). Around Tasmania, the largest storm surges occur on the south-east coast and the smallest on the northern coast. Sea level rise under a no–mitigation scenario could lead to storm surges associated with a 1-in-100 year storm tide event occurring as frequently as once every 50 years by 2030.
Potential evapotranspiration is expected to increase over Tasmania. Evapotranspiration is the combination of evaporation from soil and water surfaces, and transpiration from vegetation. An increase in aridity and drought occurrence is likely when these changes are combined with the projected declines in rainfall.
Projections show an increase in daily rainfall intensity and an increase in the number of dry days. This suggests that Tasmania’s rainfall patterns will have longer dry spells interrupted by heavier rainfall events.
Changes in severe weather vary regionally. Potential changes that may impact agriculture in Tasmania include increased flooding and fewer frosts.
TASMANIAN CLIMATE EXPERTS