North West cyclone increase may have been caused by Asian forest fires

North West cyclone increase may have been caused by Asian forest fires

28 November 2013

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Australia — When CSIRO research scientist Dr Don McFarlane looked at the Pilbara’s climate history right back to 1910, there was one period of wet weather that really stood out. From 1996 to 2001 the region had an extraordinary period of cyclone activity.

“The period between about 1996 and 2001 was very much wetter and a lot more tropical cyclones came through that period,” he says.

It was the kind of climate change that you didn’t have to be a meteorologist to notice.

“It had about a 50 percent increase in its average rainfall for that long period. And I think those people that were in the Pilbara at that time probably remember that period; a lot of the rivers were running,” he says.

Dr McFarlane says research from the Indian Ocean Climate Initiative has indicated that air pollution from Asia may be the explanation for this anomalous weather.

“Some of the wetting that has been occurring in the ’90s and early 2000s might have been a result of forest fires and pollution generally coming down from that South East Asian or even East Asian area,” he says.

Particles in the atmosphere from fires, dust and volcanoes are called aerosols and can cool large parts of the Earth’s surface. When this happens over Asia it leaves North West Australia relatively warmer, increasing moist monsoonal winds blowing towards the Pilbara and associated cyclones and rainfall.

But Pilbara cyclones caused by Asian forest fires mask the long term change to the climate which the CSIRO research is trying to uncover. The effect of aerosols on the climate is expected to be just a glitch on the longer term trend driven largely by increasing atmospheric greenhouse gas levels.

“If anything, there is a slight emphasis on the drying trend in the future. But it’s not a strong drying trend like in the south west of WA,” says Dr McFarlane.

The longer term drying trend is produced by a reduction in winter rain in the Pilbara as the climate warms.

“The cold fronts that used to come up, and in the winter bring a little bit of rain to the West Pilbara, are not getting through as much as they used to,” he says.

“But at the same time there’s been other times when there’s actually been increased rainfall in the eastern part of the Pilbara as well. So we’ll be looking at some of those trends and then trying to work out what might happen in the future,” Dr McFarlane says.

The results of the research will help communities and industry prepare for climate changes in the future.

“We’ll be using the future climate projections to see how the rivers and the aquifers may perform in time.”

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