A new study has concluded that long-term warming of the Indian and Pacific oceans worsened the deadly floods that hit Australia in 2010/11.
During the summer of 2010/11, a series of floods hit the northern Australian state of Queensland, affecting at least 90 towns, over 200,000 people, killing at least 38 people (with another 9 listed as missing at the time), and causing AUD$2.38 billion worth of damage and an estimated reduction in Australia’s GDP of about $40 billion.
Enough rain fell, in fact, to cause a filling of the rarely-filled Kati Thanda–Lake Eyre in the middle of the desert country, and even had enough of an impact to cause a drop in global sea levels.
At the time it was assumed that a hyperactive La Niña was at least partly at play behind the sheer intensity of the weather patterns behind the flooding, and now a new study by a team of US and Australian researchers working out of the Woods Hole Oceanographic Institute in Massachusetts, United States, has concluded that both a strong La Niña and a long-term ocean warning were behind the floods.
The results of the research were published in an article (How did ocean warming affect Australian rainfall extremes during the 2010/2011 La Niña event?) in the journal Geophysical Research Letters, attempting to discern the causes behind the phenomenal conditions that led to the flooding.
“The sea surface temperatures around Australia during 2010/2011 were on average 0.5°C warmer than they were 60 years ago,” said lead author Caroline Ummenhofer, a physical oceanographer with Woods Hole Oceanographic Institution (WHOI). “While many past studies have found a global warming link to heat extremes, this study is one of the first to show how ocean warming can impact a heavy rainfall event.”
The researchers determined that Australia was surrounded by extremely warm sea surface temperatures in the eastern Indian Ocean (to the west of Australia), western Pacific warm pool region (to the north and east of Papua New Guinea), and the Coral Sea (to the north-east of Australia). These warmer sea surface temperatures led to rainfall in Australia’s north-east 84% above average.
In fact, the researchers determined that all the conditions put together increased Australia’s chances of encountering rainfall this severe by a factor of three during a strong La Niña event.
“The additional warming of the oceans has profound impacts on the atmosphere,” said co-author Prof Matthew England from the ARC Centre of Excellence for Climate System Science. “It increases the amount of moisture in the atmosphere and can intensify rain-producing circulation conditions.”
“This is why in 2010/11 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.”
Of tangential interest to these findings is previous research which has concluded that increased warming of ocean temperatures in conjunction with global warming as a whole will lead to more frequent La Niña and El Niño events.
“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,” said 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.”
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