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
by Damian Carrington
Tuesday 11 January 2011 18.07
Toowoomba Flood 2011.01.10
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."