El Nino hits the skids

27 May, 2010 12:52 PM
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WITH farmers looking to the heavens over winter, there is divergence in climate forecasting models.

While the high-profile Bureau of Meteorology (BOM) forecast rainfall is for markedly lower rainfall in parts of the cropping belt, especially south-eastern Australia, other forecasting models are tipping the decline of El Nino and an average to above average rainfall year.

The BOM has tipped one final sting in the tail, following the demise of the 2009/10 El Nino event, with the national outlook for total rainfall over winter (June to August), showing a moderate to strong shift in the odds favouring a drier than normal season over a broad band stretching from the NT and WA to southeastern Australia.

The BOM forecasts, issued this week, cited recent patterns of higher than average temperatures in both the Pacific (declining El Niño) and Indian Oceans.

The influences from these two ocean patterns counteract each other in eastern Queensland and northern NSW: the Indian Ocean pattern promotes wetter conditions while the Pacific biases the climate towards a drier than normal season, meaning neutral conditions in those areas.

However, there is good news for farmers in other areas, with the major indicators including sea surface temperatures, trade winds, the Southern Oscillation Index and cloudiness over the Pacific all below El Nino thresholds and considered typical of neutral conditions.

Most forecast models are tipping a slight chance that a late season La Nina, associated with wetter conditions in Australia, may develop.

Also contradicting the BOM seasonal forecast is the latest El Nino Southern Oscillation (ENSO) report, which finds the El Niño event of 2009/10 has concluded, with all the major indicators now below El Niño thresholds.

Latest observations show that sea surface temperatures, trade winds, the Southern Oscillation Index and cloudiness over the Pacific have all returned to levels considered typical of neutral (i.e. neither El Niño nor La Niña) conditions.

Historically, about 40 per cent of El Niño events are immediately followed by a La Niña. Current conditions below the surface of the Pacific Ocean show large volumes of cooler than normal water, indicating that further cooling of the surface is likely.

And while the BOM models are forecasting drier conditions, many other tools are predicting a wetter than average winter.

Deanne Price, co-editor of the Victorian Department of Primary Industries’ (DPI) The Break newsletter, a publication dedicated to providing seasonal climate and risk information for Victorian cropping regions, said that while autumn skill in forecasting was not great, by the end of May, the models began to have more accuracy.

The Break analysed 11 forecasting models in its most recent ‘Fast Break’ newsletter, released this week.

Of these, the BOM model was one of just three that forecasted drier than average winter conditions in parts of Victoria, with the others predicting either average or above average rainfall.

“It is very difficult at this time of year to be making predictions, but none of the models predict the return of an El Nino this year and this is a good thing in terms of the increased probability of favourable seasonal conditions, especially in eastern and south-eastern Australia,” Ms Price said.

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