Sign rendered pointless by the drought. Rawnsley park station, South Australia. (Image: Peripitus)

Australia may get improved seasonal rainfall predictions, giving farmers some relief from the drought.

Scientists say that a variant of the weather pattern El Nino, the ‘Central Pacific’ El Nino, explains previously unknown variations in spring rainfall across Australia.

Harry Hendon from the Centre for Australian Weather and Climate Research said current forecast models can only distinguish between different types of El Nino up to a month ahead, but reducing model errors could extend this to several months.

“We are very optimistic that we are going to make a big advancement in our ability to predict regional climate in Australia because now we better understand there are multiple flavours of El Nino,” he said.

Deb Kerr from the National Farmers Federation said Australian farmers will welcome any improvement to rainfall forecasts: “Drought continues to challenge farmers in all respects; from a social point of view, from a financial point of view, even from a mental health point of view” she said.

“Our farmers are challenged and looking for opportunities to put into practice what they can to enhance and protect their businesses.”

El Nino is traditionally related to warmer than normal ocean temperatures in the eastern Pacific near the equator, but in 2004 Japanese researchers identified an El Nino centred in the central Pacific. They called this El Nino “Modoki” after a Japanese word which means “similar, but different”. Hendon said the name ‘Central Pacific El Nino’ is more appropriate because it indicates a better understanding of the processes involved.

During El Nino, thunderstorm activity near the equator shifts from close to Australia into the eastern Pacific. These thunderstorms lift air high into the atmosphere where it spreads out, cools, and descends, causing more air than normal to sink over the Australian continent. Sinking air is associated with high atmospheric pressure and less rainfall, which can lead to drought for farmers. Current forecasts of El Nino tend to underestimate this effect during Central Pacific El Nino events.

A recent study published in the journal Nature has also found that climate change is responsible for an increase in the frequency of ‘Central Pacific’ El Nino events since 1990 and that the ratio of Central Pacific events to Eastern Pacific events will increase as global warming continues.

“How [El Nino] works is super-imposed upon some mean climate” said Ben Kirtman, one of the study’s authors and Professor of Meteorology and Physical Oceanography at the University of Miami.

“The mean background state has changed, so that’s why we’re seeing more of these Central Pacific El Ninos.”

Hendon said this does not necessarily mean Australia will experience more droughts.

“We’re definitely going to need to tackle this problem of model bias and the ability to tell the difference between the El Nino events to be able to make better seasonal forecasts but … we suffer drought under both sorts of El Nino,” he said.

“What we’ve tried to emphasise is that using traditional measures of El Nino may not be a good indication of what the impacts on Australia might be.”

The Bureau of Meteorology website reports that the Pacific Ocean is currently experiencing an El Nino event and they predict that it will last until early 2010. The NSW Department of Primary Industries drought map shows that 68% of the state is in drought, up from 64% in August. Kirtman said that there is a high probability that El Nino will be followed by its opposite phase “La Nina” in 2010 or 2011, which usually brings wetter conditions for eastern Australia. Another El Nino event would be very unusual but “nothing’s impossible. Mother Nature always gives us a surprise”.