According to the Indian Ocean Climate Initiative (IOCI) - a partnership of the State Government of Western Australia, CSIRO, and the Bureau of Meteorology - the region's climate is likely to continue to become warmer and drier over coming decades due to the increase in greenhouse gases.

CSIRO Marine and Atmospheric Research scientist, Dr Bryson Bates, says there is increased confidence in how the climate of south-west Western Australia will change due to increasing greenhouse gas concentrations, but that the IOCI team will now do further work to understand climate change across the whole of the state.

"The next phase of IOCI will be a much bigger research effort than ever before," Dr Bates says. "Following the great strides forward we have made in understanding the climate of the south-west, we will now investigate other aspects of the West Australian climate, particularly in the economically important north-west."

"We need to improve our understanding of the contribution to climate change in the region from factors such as the Asian Brown Cloud, and improve our understanding of tropical cyclones in the north-west."

Dr Bates says the IOCI research team have already used climate projections from nine climate models to understand how climate may change in the south-west.

"Our results show that by 2030 there would be a rise in temperatures in all seasons and a decrease in winter rainfall," he says. "Rainfall may decline by as much as 20 per cent relative to the 1960-1990 level, with the number of winter rain days decreasing by up to 17 per cent, and runoff in south-west WA catchments consequently decreasing by between five and 40 per cent."

"By about 2085, these changes may further increase, with rainfall declining by between five and 34 per cent, and the number of winter rain days decreasing by up to 30 per cent," Dr Bates says.

Dr Pandora Hope, from the Bureau of Meteorology Research Centre, says that IOCI's results also provide increased confidence in the causes of recent past climate changes in south-west Western Australia.

"The sudden decline in south-west Western Australian early winter rainfall that occurred in the 1970s, and has continued since, is occurring because the potential for storm development over this region has decreased due to much weaker winds in the upper atmosphere," Dr Hope says. "In the next phase we will investigate how much of this change might be explained by natural variations in the climate or if this is a consequence of human activity."

The researchers also identified that since the mid-1970s there has been a decrease in the number of winter weather systems that bring wet conditions and an increase in the number of systems that bring dry conditions.

"It's unlikely the observed warming is a result of natural climate variability alone," Dr Hope says. "And the observed rainfall decline in south-west WA is likely to have been caused by both natural fluctuations and increases in greenhouse gas concentrations."

As announced today by the WA Environment and Climate Change Minister David Templeman, the next phase of IOCI will continue until 2011 to help decision-makers make plans to adapt to future climate change and variability.

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