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NatureScience

La Nina to Continue through First Quarter of 2011

A report from the UN’s weather agency, the World Meteorological Organization, has reported that the current La Nina event will last through the first quarter of 2011, and possibly into the second quarter.

However, the report noted that “the strength of the event is likely to decrease during the course of the coming 4 months.”

Atmospheric indicators show this episode to be one of the strongest of the last century, states the report, while oceanic indicators have been at moderate to strong levels.

Moderate to strong La Niña conditions have continued since August 2010, with sea surface temperatures averaging around 1.5 degrees Celsius cooler than normal in the east-central tropical Pacific. Markedly strengthened trade winds and much reduced cloudiness indicate a strong coupling between the ocean and overlying atmosphere.  As typically observed with the advent of the mature stage of La Niña, sea surface temperatures in the western tropical Pacific and eastern Indian Ocean have risen to well above their averages, while those in the western Indian Ocean have become below average.

The subsurface waters of the central and eastern equatorial Pacific also continue to reflect moderate to strong La Niña conditions, with temperatures of 1 to 5 degrees Celsius below average down to a depth of 150 meters. This large volume of anomalously cold water is likely to maintain the existing cooler than average ocean surface temperatures.

“In atmospheric terms it has to be termed one of the strongest ever La Nina episodes,” said Rupa Kumar Kolli, head of world climate services at the World Meteorological Organisation. “The most important impacts we have witnessed in recent months have been the devastating floods in Australia.”

Australia has suffered flooding in all three of its eastern continental states, with 35 people killed in Queensland, an additional nine still missing, and 70 towns with 200,000 people affected. Currently, the estimated damage cost is around $1 billion AUD, and the Australian gross domestic product will suffer a reduction of $30 billion AUD.

The Queensland floods were immediately followed by flooding in the western and central parts of Victoria, where more than 51 communities have been affected by flooding, with a total of 1,730 properties being flooded and hundreds of roads and train services being cancelled. The damage bill for Victoria currently rests at an estimated $2 billion AUD.

This La Nina is also believed to be linked to above average rainfall in southern Africa, below average rainfall in eastern equatorial Africa, and below average rainfall in central southwest Asia and southeastern South America.

In light of the above assessment, regions typically impacted by La Niña events are advised to take note of the expected continuation of moderate to strong La Niña conditions over the coming 1-2 months, concluded the report, and weaker La Niña conditions during March and April. Consultation of local climate outlooks provided by the respective regional and national agencies is recommended for the best information on management of climate-related risks.

Source: UN World Meteorological Organization [report available here (.doc)]
Image Source: robstephaustralia




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