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Surprise floods: Water rushing through Aplin's Weir in Townsville
on January 11, 1998.
Photo: Greg Calvert
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In the middle of last year weather forecasters were predicting a
late and "dry" wet season for the tropical savannas because of the
El Nino phenomenon - so what went wrong?
Parts of the Top End and Cape York Peninsula have had near record
wet season rainfalls. Katherine, Normanton and Townsville all had
serious flooding. Which raises an important question: should people
in the top of Australia now view El Nino forecasts as having as
much relevance to them as fortune cookie predictions?
Well, the climate specialists say not necessarily, it just requires
understanding the El Nino and discarding a few myths.
El Nino affects the whole of the country in the same way
According to the Bureau of Meteorology, an El Nino event actually
affects different parts of the country more reliably at different
times of year. In the north an El Nino is usually a good predictor
of less rainfall in the build-up to the wet; in SW Western
Australia it's normally a good predictor of a dry autumn. But these
predictions are still only good for about 70 per cent of the time.
Last year's build-up in northern Australia was one of those 30 per
cent of cases where the El Nino prediction went astray - but it
hasn't dented the confidence of the Bureau's climate researchers in
the validity of their El Nino models.
This El Nino—'the climate event of the century'—has
been an over-hyped dud.
When its global impact is taken into account this year's El Nino
may live up to the hype. It has been more severe in some ways than
the big one of 1982/83, which was the most intense so far this
century. According to the US National Oceanic and Atmospheric
Administration (NOAA) this year's event saw ocean temperatures in
the Pacific reach record highs of 5 degrees above average. The El
Nino also had a greater impact on atmospheric circulation than in
1982/83. There were severe storms and floods in North and South
America, and drought in PNG and Indonesia.
The SOI Index sums up El Nino
The Southern Oscillation Index (SOI) is the difference between the
standardised Tahiti Sea Level Pressure (SLP) and the standardised
Darwin SLP. Although this difference reflects many of the broad
changes in sea temperatures and atmospheric circulation that occur
during an El Nino, it doesn't give the whole story. In the current
El Nino the monthly SOI figures have not reached the low levels of
1982/83, yet changes in sea surface temperature and atmospheric
circulation in the eastern Pacific have been more pronounced than
in 1982/83.
The take-home message from the climate agencies? El Nino climate
forecasts are a lot more useful than fortune cookies forecasts but
it helps to put them in their proper context.
