Sydney set for another heatwave

Last updated 13:45 05/01/2013
sydney weather

Hot in the city: Lou Pagano, a high school science teacher at St Patricks College in Sutherland rises early to catch the sunrise at Coledale Beach. Sydney is in for a scorching summer.

A paddleboarder enjoys the hot weather at Bondi Beach in Sydney.

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At first glance, you don't get more typical years than last year.

Some 1215 millimetres of rain fell on Sydney's Observatory Hill, just 2 millimetres shy of the site's annual averages which go all the way back to 1858.

And nationwide, temperatures came in just 0.11 degrees above the mean for the 1961-90 period, while rainfall was 2.3 per cent higher.

Breaking down the statistics for Sydney and the nation, though, and some significant changes appear to be under way.

It seems the past two wet and relatively cool years associated with the La Nina climate patterns were temporary departures from the new norm.

"It's very clear that the whole of southern Australia is experiencing a quite profound change in the seasonal cycle of rainfall," said David Jones, manager of climate monitoring and prediction at the Bureau of Meteorology.

"We've just reverted to this climate pattern that dominated in the 1990s and into the early 2000s, which is below average rain during late autumn, winter into spring."

Last year was a year of two halves for much of the country, including Sydney.

More than 80 per cent of the city's annual tally fell in the first half of the year.

The flower beds started drying out after that, with just 225.6 millimetres recorded between July and December.

And soakings disappeared too, with no recordings of 25 millimetres of rain in a day in the second half, compared with four to five in a normal year and 12 such events in the first six months of the year.

Temperatures for the city also warmed up after an average start to the year as the La Nina climate pattern started to ease. From April the mercury topped the norm, leaving an average maximum for the whole of the year of 22.7 degrees - which was 1 degree above the mean.

National figures tell a similar story of a year that started out relatively cool and wet before the conditions turned sharply hotter and drier.

Summer, in effect, came early with Australia posting a record average maximum for the final four months of the year.

This year has barely begun but the current extreme heatwave across much of the country could break records for the average maximum and the hottest maximum for any location.

Several all-time records fell on Friday, including Hobart where mercury soared to 41.8 degrees. Adelaide sweltered in 45 degree heat, the fourth hottest day there since records began in 1887.

The weather bureau predicts summer will be warmer than usual.

"All of NSW is expecting above-average temperatures" until March, said Aaron Coutts-Smith, the bureau's NSW manager for climate services.

Will Steffen, from the Climate Commission, said the cooler La Nina climate conditions of 2010 and 2011 did not signify a departure from ''the underlying multi-decadal warming trend''.

''We would expect to see quite intense dry periods in the south-eastern parts of the continent because the autumn and winter rainfalls do not look like coming back to normal, no matter what, even during the La Nina years.''

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While the longer-term rainfall outlook for NSW and Queensland is unclear, Professor Steffen says the outlook for much of the rest of Australia suggests a slide back to the very dry conditions of the past decade or so.

The weather bureau's Dr Jones said southern Australia’s weather systems are shifting towards Antarctica, much as climate change models would suggest, although the general drying of the region is on the high end of forecasts.

“The current rate of drying is rather more rapid than most models would seem to predict,” he said.

- Sydney Morning Herald


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