Double-barelled La Nina brings third wettest year

Beef Central, 05/01/2012

Click on video to watch the Weather Channel's summary of Australian weather conditions for 2011.



A double-barrelled La Nina made 2011 the third wettest year in Australia since records commenced in 1900, according to the Bureau of Meteorology’s annual Australian Climate Statement released yesterday.

Average Australian rainfall for 2011 was 699mm (28 inches), a hefty 234mm or 34 percent higher than the long term average of 465mm (16.6 inches).

The La Nina patterns that bookended the year and record warm eastern Indian Ocean temperatures contributed to the higher than average rainfall.

Consistent with the La Nina events, the year was charactertised by wetter than average summers.  

Most areas of Australia received rainfall well above average from January to March, while April was wet over northern Western Australia and the Northern Territory.

Falls greater than 300mm across much of the tropical north led to the wettest March on record for Australia as a whole, with average rainfall of 149mm.  That topped the previous record set in 1989 by 23mm.

However rainfall dropped to below average levels for the five months from May to September.

The return of a La Nina pattern brought wetter conditions again in spring, particularly across the western half of the country, with Western Australia recording its third-wettest October on record.

November rainfall was above average for most of the country, while December was wet for the southwest and parts of Queensland.

For the year as a whole, the majority of Australia received above average rainfall; the only regions with below-average rain were patches of southwest Western Australia, western Tasmania and pockets of New South Wales and southeast Queensland.

Average mean temperatures were 0.14 degrees Celcius cooler than the 1961 to 1990 average of 21.81 degrees Celcius. The statement noted that it was the first time since 2001, also a wet La Nina year, that Australia’s mean annual temperature was below the 1961-90 average.

Contrasting this, the global mean temperature was the highest for any year which began with a La Nina. Australia was one of the few places in the world to experience cooler than average temperatures in 2011.

Meanwhile the bureau yesterday reported that the current La Nina over the tropical Pacific Ocean may be close to its peak, with a gradual decline expected over the remainder of the summer and early autumn.

The bureau said that despite some cooling at the surface of the tropical Pacific over the past fortnight, which is indicative of a strengthening La Niña pattern, sea surface temperatures were now warmer and therefore less extreme than they were at the same time last year.

Atmospheric indicators of La Niña also strengthened slightly over the last fortnight, with the Southern Oscillation Index (SOI) monthly December value of +23 being the highest value since the breakdown of the 2010-11 event in autumn 2011.


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