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: Climate change could wipe out Australian mammals

Related Stories

Climate change could wipe out Australian mammals

June 5, 2015

Australian native animals could be under threat of extinction from climate change, with a unique longitudinal study by Deakin University scientists finding our small mammal populations are suffering the ravages of long-term ...

NASA-led volunteers map landslides by Nepal quakes

June 3, 2015

As millions of people regroup from the impact of the earthquakes in Nepal, a team of international volunteers is combing through satellite imagery of the region to identify additional hazards—earthquake-induced landslides.

Blueprint for a thirsty world from Down Under

May 26, 2015

The Millennium Drought in southeastern Australia forced Greater Melbourne, a city of 4.3 million people, to successfully implement innovations that hold critical lessons for water-stressed regions around the world, according ...

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

January 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 you might not ...

Recommended for you

Climate ups odds of 'grey swan' superstorms

August 31, 2015

Climate change will boost the odds up to 14-fold for extremely rare, hard-to-predict tropical cyclones for parts of Australia, the United States and Dubai by 2100, researchers said Monday.

Quantifying the impact of volcanic eruptions on climate

August 31, 2015

Large volcanic eruptions inject considerable amounts of sulphur in the stratosphere which, once converted into aerosols, block sun rays and tend to cool the surface of the Earth down for several years. An international team ...

0 comments

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.