Tomorrow’s forecast: warmer, drier, windier

Global warming will make Tasmania warmer, windier and, for most of us, drier, according to modelling by CSIRO’s Dr Peter McIntosh. [2 October 2007 | Peter Boyer]

Dr Peter McIntosh (Photo Bruce Miller)

Dr Peter McIntosh (Photo Bruce Miller)

Hobart climate scientist Dr Peter McIntosh knew he was taking on a tough assignment when Hydro Tasmania approached him a few years ago and asked him to find out what will happen to our climate over the next 35 years or so.

For one thing, Tasmanian conditions are notoriously difficult to predict – even for days or weeks ahead – because of its varied topography and the many dynamic forces in play at any given time in Southern Ocean latitudes.

Another problem was scale. The interactions of forces over time that make up our climate are so complex that long-term climate modelling tends to work at a “big picture” scale, where Tasmania barely rates more than a glance.

Climate predictions using standard global models represent Tasmania as one or two grid cells. Hydro Tasmania needed to differentiate between various parts of the State down to a resolution of 10 or 20 kilometres.

A solution came from within Dr McIntosh’s own CSIRO Division of Marine and Atmospheric Research, where scientists have developed a variable-resolution climate model capable of providing fine resolution over a relatively small area like Tasmania.

Tasmanian data on temperature, rainfall and wind going back many decades were used to calibrate the model. Then, estimates of future greenhouse gas emissions were fed into the model to develop likely scenarios from the present time to 2040 to help Hydro Tasmania plan its future with more certainty.

Dr McIntosh is careful to point out that no modelling provides a perfect prediction, and that best results are obtained by using multiple models and emission estimates. But the predictions are a sobering reminder that we in Tasmania are far from immune from the impact of global climate change.

•    On average, we can expect higher temperatures – up to half a degree higher by 2040 – especially at night.

•    We should anticipate between 10 and 20 percent less rainfall in all our major centres. On the other hand, rainfall in the South-West is likely to increase by about 10 percent, taking in several important Hydro catchment areas.

•    Wind speeds are likely to increase by up to 5 percent everywhere, which is good for wind-power but not so good for evaporation and soil moisture.

One of the underlying messages of Dr McIntosh’s modelling is that with higher temperatures and wind speeds, we can expect decreasing water availability from catchments in Tasmania’s eastern half. That’s serious food for thought.

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