CSIRO has begun estimating long-range probabilities of receiving above or below median rainfall over much of Australia, based on forecasts of whether El Niño or La Niña conditions will develop in the Pacific Ocean.

"We use sophisticated climate models run on a supercomputer to predict sea surface temperatures in the equatorial Pacific Ocean. These temperatures provide a measure of the strength of El Niño and La Niña," says Dr. Ian Smith of CSIRO Atmospheric Research.

"Our predictions build on over a decade's climatic research by CSIRO," Dr. Smith says.

La Niña conditions prevailed up until late last year and were accompanied by significantly above-average rainfall over much of Australia. In fact, 2000 was classified as the second wettest on record. Since then, La Niña conditions have waned.

"Everyone is asking when the next El Niño event will occur," says Dr. Smith.

Typically, El Niño means drier than normal conditions over much of eastern and northern Australia. The last El Niño was in 1997. CSIRO predicts neutral conditions (neither El Niño or La Niña) through to autumn of 2002.

CSIRO will update its predictions monthly.

"The predictions are sometimes skillful up to 9 months ahead in time but at this time of year it is too early to make skillful predictions for winter 2002," says Dr. Smith, "but we are closely checking for signs that an El Niño may develop next year".

The National Climate Center and the Queensland Center for Climate Applications provide rainfall outlooks three months ahead.

"CSIRO is generating information beyond three-months ahead, which can be useful for agricultural, water resource and agribusiness planners," says Dr. Smith.

The Commonwealth Government's Climate Variability in Agriculture Research and Development Program helped fund this research.

El Niño events occur irregularly every 2 to 7 years. Unusually warm sea surface temperatures in the eastern Pacific Ocean initiate them. Accompanying this temperature change, moist winds that blow across the Pacific towards Australia slacken. As a result, rainfall over much of Australia declines.

El Niño's counterpart, La Niña, is often responsible for above average rainfall, especially in the eastern States. La Niña is associated with a warming of the ocean north of New Guinea and a cooling of the surface of the eastern Pacific Ocean. This favors moist winds that often bring us rain.

These El Niño and La Niña predictions complement the specialized industry-based predictions recently announced by CSIRO. The CSIRO long-lead predictions are available from this URL. - By Bianca Nogrady

[Contact: Ian Smith, Paul Holper, Bianca Nogrady ]

29-Nov-2001