A team of U.S. and Australian researchers reveals that the long-term warming of the Indian and Pacific oceans plays an important role in increasing the risk of devastating floods, such as what happened in Australia in 2010/2011.

The study, which was published in Geophysical Research Letters, is one of the first to show how ocean warming can impact a heavy rainfall event, according to researchers from the Woods Hole Oceanographic Institution (WHOI).

Recorded to be among the worst floods in the country’s history, the 2010/2011 floods in the northeast state of Queensland claimed 35 lives and caused $2.38 billion damage. As a result of heavy rains, it led to a rare filling of Lake Eyre, a large lake system in the interior of the country and caused a drop in global sea level.

The sea surface temperatures around Australia during 2010/2011 were on average 0.5°C warmer than they were 60 years ago, says the study’s lead author Caroline Ummenhofer, a WHOI physical oceanographer.

In the summer of 2010/2011, the country was surrounded by extremely warm sea surface temperatures, particularly in the eastern Indian Ocean, western Pacific warm pool region and the Coral Sea. Despite being an average cyclone season, rainfall in Australia’s northeast during that time was 84 per cent above average and soil moisture measurements were the highest recorded since 1950.

Ummenhofer and her colleagues ran numerical experiments to try to understand how different factors contributed to the unusual 2010/2011 conditions. Their research determined that due to warmer sea surface temperatures, Australia was three times as likely to get this much rain during a strong La Niña event.

“The additional warming of the oceans has profound impacts on the atmosphere. It increases the amount of moisture in the atmosphere and can intensify rain-producing circulation conditions,” says co-author Professor Matthew England from the ARC Centre of Excellence for Climate System Science.

He explains that this is why in 2010/2011, more moisture was brought onshore along Australia’s east coast. Stronger rising motion over the northeast resulted in higher rainfall, making it more likely for Australia to suffer extreme rainfall conditions during this strong La Niña, England says.

In addition to the warming oceans bringing more rainfall, previous research has also shown that as a result of global warming, strong La Niña and El Niño events are likely to become more frequent.

Australia has long been acknowledged as a country of extremes, but this research suggests extreme rainfall events may become far more frequent in a warming world, according to Ummenhofer. “As we come into climate change talks in Paris, this research offers yet another incentive for countries around the world to take action to forestall global warming,” she says.

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