Australia floods: La Niña to blame

The country is in the in the grip of an unusually strong periodic climate phenomenon that brings heavy rains
Damian Carrington guardian.co.uk 11 Jan 11;

The devastating flooding in Queensland is the result of Australia being in the grip of an unusually strong "La Niña", a periodic climate phenomenon that brings more rain to the western Pacific, and less to South America along the eastern Pacific.

"The Queensland floods are caused by what is one of the strongest – if not the strongest – La Niña events since our records began in the late 19th century," said Prof Neville Nicholls at Monash University and president of the Australian Meteorological and Oceanographic Society. "The La Niña is associated with record warm sea-surface temperatures around Australia and these would have contributed to the heavy rains." Warmer oceans produce damper air and hence more rain. This is driven onshore by the stronger east-to-west trade winds characteristic of La Niña.

These weather patterns led to December being the wettest ever recorded in Queensland and to Australia having its third wettest year. The Australian Bureau of Meteorology predicts that La Niña is likely to persist into the southern hemisphere autumn, raising the possibility of further torrential downpours.

La Niña, "the girl" in Spanish, is named in reference to its counterpart, El Niño – "the Christ Child". Here the climatic conditions are reversed, with warmer, wetter weather over South America which is usually first noticed at Christmas by fishermen off Peru. La Niña occurs at intervals between a few years and a decade and generally lasts for a year or two. What causes the switch is not known, but it is thought to arise from the complex interaction of ocean and atmospheric circulations.

"This is one of the strongest La Niña events in the past half century," said Bill Patzert, a climatologist at Nasa's Jet Propulsion Laboratory. "Impacts include heavy rains and flooding, which has damaged crops and flooded mines in Australia and Asia. It also has resulted in flooding in northern South America and drought conditions in Argentina. This powerful little lady is spreading her curses and blessings across the planet. She's the real deal."

A silver lining in the storm clouds brought by La Niña is the relief of the decade-long drought much of Australia has endured. There was a dramatic recovery in water storages across the Murray-Darling Basin in eastern Australia from 26% full at the start of 2010 to 80% at the start of 2011. However, elsewhere in the country, south-western Australia suffered its driest year on record in 2010, continuing decades of drying.

"The extent to which any of this – the floods, warm oceans, or very strong La Niña – is linked to global warming is unknown, because the requisite studies to test this have simply not been done yet," said Nicholls.

But as a general point, said Prof Vicky Pope, head of climate change advice at the Met Office, a warmer world is a wetter world. "As the average global temperature increases one would expect the moisture content of the atmosphere to rise, due to more evaporation from the sea surface. For every 1C sea surface temperature rise, atmospheric moisture over the oceans increases by 6-8%. Also in general, as more energy and moisture is put into the atmosphere [by warming], the likelihood of storms, hurricanes and tornadoes increases."

Scientists See Climate Change Link To Australian Floods
David Fogarty, PlanetArk 13 Jan 11;

Climate change has likely intensified the monsoon rains that have triggered record floods in Australia's Queensland state, scientists said on Wednesday, with several months of heavy rain and storms still to come.

But while scientists say a warmer world is predicted to lead to more intense droughts and floods, it wasn't yet possible to say if climate change would trigger stronger La Nina and El Nino weather patterns that can cause weather chaos across the globe.

"I think people will end up concluding that at least some of the intensity of the monsoon in Queensland can be attributed to climate change," said Matthew England of the Climate Change Research Center at the University of New South Wales in Sydney.

"The waters off Australia are the warmest ever measured and those waters provide moisture to the atmosphere for the Queensland and northern Australia monsoon," he told Reuters.

The Queensland floods have killed 16 people since the downpour started last month, inundating towns, crippling coal mining and are now swamping the state's main city of Brisbane.

The rains have been blamed on one of the strongest La Nina patterns ever recorded. La Nina is a cooling of ocean temperatures in the east and central Pacific, which usually leads to more rain over much of Australia, Indonesia and other parts of Southeast Asia.

This is because the phenomena leads to stronger easterly winds in the tropics that pile up warm water in the western Pacific and around Australia. Indonesia said on Wednesday it expected prolonged rains until June.

WEATHER SWITCH

The Pacific has historically switched between La Nina phases and El Ninos, which have the opposite impact by triggering droughts in Australia and Southeast Asia.

"We've always had El Ninos and we've had natural variability but the background which is now operating is different," said David Jones, head of climate monitoring and prediction at the Australia Bureau of Meteorology in Melbourne.

"The first thing we can say with La Nina and El Nino is it is now happening in a hotter world," he told Reuters, adding that meant more evaporation from land and oceans, more moisture in the atmosphere and stronger weather patterns.

"So the El Nino droughts would be expected to be exacerbated and also La Nina floods because rainfall would be exacerbated," he said, though adding it would be some years before any climate change impact on both phenomena might become clear.

He said the current La Nina was different because of the warmest ocean temperatures on record around Australia and record humidity in eastern Australia over the past 12 months.

Prominent U.S. climate scientist Kevin Trenberth said the floods and the intense La Nina were a combination of factors.

He pointed to high ocean temperatures in the Indian Ocean near Indonesia early last year as well as the rapid onset of La Nina after the last El Nino ended in May.

"The rapid onset of La Nina meant the Asian monsoon was enhanced and the over 1 degree Celsius anomalies in sea surface temperatures led to the flooding in India and China in July and Pakistan in August," he told Reuters in an email.

He said a portion, about 0.5C, of the ocean temperatures around northern Australia, which are more than 1.5C above pre-1970 levels, could be attributed to global warming.

"The extra water vapor fuels the monsoon and thus alters the winds and the monsoon itself and so this likely increases the rainfall further," said Trenberth, head of the Climate Analysis Section at the National Center for Atmospheric Research in Boulder, Colorado.

"So it is easy to argue that 1 degree Celsius sea surface temperature anomalies gives 10 to 15 percent increase in rainfall," he added.

Some scientists said it was still too soon to draw a definite climate change link to the floods.

"It's a natural phenomena. We have no strong reason at the moment for saying this La Nina is any stronger than it would be even without humans," said Neville Nicholls of Monash University in Melbourne and president of the Australian Meteorological and Oceanographic Society.

But he said global atmospheric warming of about 0.75C over the past half century had to be having some impact.

"It has to be affecting the climate, regionally and globally. It has to be affecting things like La Nina. But can you find a credible argument which says it's made it worse- I can't at the moment."

(Editing by Robert Birsel)

NASA says La Nina fueling Australia floods
Yahoo News 14 Jan 11;

WASHINGTON (AFP) – The US space agency said Thursday that a particularly strong La Nina weather pattern of cooler water temperatures is fueling heavy rains and floods in Australia.

"Although exacerbated by precipitation from a tropical cyclone, rainfalls of historic proportion in eastern Queensland, Australia have led to levels of flooding usually only seen once in a century," said David Adamec, oceanographer at NASA's Goddard Space Flight Center.

"The copious rainfall is a direct result of La Nina's effect on the Pacific trade winds and has made tropical Australia particularly rainy this year."

NASA is monitoring weather patterns via satellite images which show a strong La Nina pattern in November and December 2010.

"The solid record of La Nina strength only goes back about 50 years and this latest event appears to be one of the strongest ones over this time period," said climatologist Bill Patzert of NASA's Jet Propulsion Laboratory in California.

"It is already impacting weather and climate all around the planet."

Australia's third-largest city Brisbane was reeling Thursday with whole suburbs under water and infrastructure smashed as the worst flood in decades hit 30,000 properties.