Understanding autumn rain decline in SE Australia

May 23, 2008
Understanding autumn rain decline in SE Australia
CSIRO Marine and Atmospheric Research scientist, Dr Wenju Cai

According to a report from a CSIRO Wealth From Oceans Flagship study – published this week in the science journal Geophysical Research Letters – since 1950 Victoria has suffered a 40 per cent decline in autumn rainfall (March to May) compared to the average recorded between 1961–90.

The report’s authors, CSIRO’s Dr Wenju Cai and Tim Cowan, say that the decline has been most prominent in May, which accounts for about half of the total seasonal reduction.

The identified causes show imprints of climate change influences, in part through a reduction in the number of La Niña events, and in part through changing weather systems originating from the subtropical Indian Ocean that are conducive to late autumn rainfall across Victoria.

The researchers found that since 1950 the spatially alternating high and low pressure systems (called pressure wave-trains) conducive to rainfall over southern Victoria in May have been weakening, leading to rising sea level atmospheric pressure over south-east Australia.

“This weakening is reinforced by a warming of the Indian Ocean, which is at least in part due to global warming,” Dr Cai says. “This suggests that a component of climate change is active in southern Victoria receiving less rainfall.”

Influences from the Indian Ocean sector occur in conjunction with those from the Indonesian Throughflow region, to the north of Australia. Dr Cai says higher sea surface temperatures in the Throughflow region are conducive to rainfall in central and northern south-east Australia, through the familiar tropical northwest cloud bands, which deliver rainfall to the region.

“Through April and May, large increases in sea surface temperatures in the region are usually associated with a transition from an El Niño to a La Niña event, as part of cycle of the El Niño-Southern Oscillation,” he says.

Mr Cowan says that in recent decades, there have been more El Niño events than La Niñas. As the system spends more time in an El Niño phase, and less time transitioning to a La Niña, south-east Australia receives less rainfall. “This El Niño-like behaviour pattern of the Pacific system is also consistent with what is expected from climate change, as recent studies have shown,” he says. Victoria is not alone among states experiencing rainfall declines. During the past 50 years there has been a decreasing trend in rainfall over much of Australia. In south-west Western Australia the trend is strongest in winter; and in southern Queensland strongest in summer.

Source: CSIRO Australia

Explore further: Ancient deformation of the lithosphere revealed in Eastern China

add to favorites email to friend print save as pdf

Related Stories

Who's been affected by Australia's extreme heat? Everyone

Jan 30, 2015

Australia has been hit by two years of heat: 2013 was the hottest ever recorded and 2014 wasn't far behind, taking third place. The country has also sweltered through several significant heatwaves, and, though ...

Bushfires follow Australia's third-hottest year

Jan 06, 2015

Australia experienced its third-hottest year on record in 2014, paving the way for an early start to the bushfire season, scientists said Tuesday as hundreds of firefighters battled blazes in three states.

New dawn for pasta wheat in Australia

Sep 17, 2014

The University of Adelaide's durum breeding program today at the Hart Field Day will release a new durum wheat variety called DBA-Aurora which promises a step-change in potential durum production in southern Australia.

New analysis links tree height to climate

Aug 14, 2014

What limits the height of trees? Is it the fraction of their photosynthetic energy they devote to productive new leaves? Or is it their ability to hoist water hundreds of feet into the air, supplying the ...

Recommended for you

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.