El Niño jury is still out

Photo of Grant Beard (left) and Dr Andrew Watkins, consulting the latest weekly Sea Surfact Temperature (SST) map of the Pacific Ocean

[Photo: Grant Beard (left) and Dr Andrew Watkins, senior climatologists with the National Climate Centre at the Bureau of Meteorology, consult the latest weekly Sea Surface Temperature (SST) map of the Pacific Ocean before writing the ENSO Wrap-Up. SSTs from this region are vital for the forecasting of future climate in the Australasian region.]

If you think that climate scientists cannot make up their mind about whether there will be an El Niño this year, you are right.

In fact we should be suspicious of anyone who claims their mind was made up about El Niño back in autumn. The interaction between the ocean and atmosphere is complex and dynamic; small changes can result in very different outcomes.

This is why climate scientists should keep their opinions and observations to themselves, and wait until late winter before making a safe call on El Niño.

As an agronomist with a special interest in climate, I used to pester friends in the Bureau of Meteorology and other climate scientists over this autumn period. I knew that they could not give me a firm answer, but I also knew that they had access to the most recent measurements and models and was interested in what they were thinking.

Since 2001 anyone with access to the web can find out what climate scientists are thinking by checking the ENSO Wrap-Up www.bom.gov.au/climate/enso/. Indeed, farmers with web access now have more information at their fingertips than the most advanced climate lab did a decade ago. This is great but it can lead to information overload.

One of the benefits of the ENSO Wrap-Up is that it helps with interpretation and aims to give a balanced view of factors that would support or not support an El Niño developing.

This season there is a heightened interest in El Niño. Recent years have been pretty tough; there are mixed levels of stored soil water across the region and the first half of autumn has been one of the hottest and driest on record.

What to read into a 50 per cent chance of El Niño?

Some people under-react and say "So what, 50:50 is hardly a commitment." In the past 100 years there have been about 24 El Niño events - so each autumn we can say that the odds for an El Niño are about one in four. If the odds are set at 50 per cent, this doubles the chances of an El Niño.

Others will over-react and say that there is a 50 per cent chance of a 2002-type drought.

It is important to recognise that there are more El Niño events than bad droughts. If a bad drought is defined as one in 10 or 20, this is much rarer than an El Niño, which is one in four. El Niño is best understood as increasing the risk of bad drought.

As the season progresses over autumn, wise farmers consider a number of factors such as price information, stored soil water and the timing of the break.

A farmer told me he marks on his calendar the date when the ENSO Wrap- Up comes out, as he finds it helpful to know what the scientists are thinking so he can factor it into his decision making.

GRDC Research Code LWR25
For more information: Dr Peter Hayman, principal scientist, Climate Applications, SARDI, hayman.peter@saugov.sa.gov.au