(Transcript from SBS World News Radio)
The Bureau of Meteorology has declared the start of an El Nino weather event, the precursor to what is often the cause of some of Australia's most severe droughts.
Aileen Phillips reports.
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For the first time in almost six years, Australia is set to face the impacts associated with the El Nino weather event.
Based on Bureau of Meteorology research so far, the El Nino event appears set to stay at least until spring, with most of the effects to be felt in the country's east.
Forecast models from around the world also suggest the El Nino will probably have a significant impact, with the Bureau predicting what it calls a moderate to strong event.
Typically, the event means fewer tropical cyclones and a reduced risk of widespread flooding.
Dr David Jones is a senior climatologist with the Bureau of Meteorology's climate information services branch.
He says one key factor in determining an El Nino is an increase in sea-surface temperatures.
"It's a box in the central Pacific, just on the edge of what we call the 'warm pool'. And, when this region warms, it typically means the onset of El Nino-like conditions. The typical threshold we look at for this box region is about 0.8 degrees, and, certainly, at this moment in time, we've clearly met that definition. The Pacific now has been about a degree to a little bit over a degree warmer than average for more than a month and continues to be above average."
Dr Jones adds that trade winds also play a part in determining an El Nino event.
"How strongly the winds are blowing from the eastern Pacific to the western Pacific. And we've seen sustained weaker trade winds now for a number of months, and that tells us not only is the atmosphere feeling the effects of the sea surface but we're also getting the feedback from the atmosphere onto the sea-surface temperatures."
He says the event is associated with warmer days, less rainfall and a reduced risk of widespread flooding, among other effects.
"Increased frost risk in the middle of winter, and that's because the soils are usually dry and we usually get less cloud cover. So you get this interesting phenomenon of hotter days but often cooler nights, particularly during the early spring and winter periods. As far as snow cover, looking back over time, most of the poorer ski seasons are associated with El Nino events, so warmer days in spring tend to lead to earlier snow melt, and drier conditions during winter/spring tend to lead to reduced snow, snowfall."
The Bureau of Meterology's Dr Lynette Bettio says, given that drought is also highly likely, the Bureau will closely monitor water resources.
"Looking at the Murray Darling basin, we're starting to see this attrition of average to below average rainfall year after year. Since it was filled again from the 2010/2011 La Nina event, we are starting to see that slowly go down. So we're starting to see it approach the levels of what we saw in 2010, towards the end of that millennium drought period."
Below average rainfall and warmer daytime temperatures also generally mean an earlier start to the fire season, particularly in south-eastern Australia.
But David Jones says it is not all bad news.
"Tropical cyclones tend to be less frequent during El Nino summers. So we would expect, with this El Nino event continuing to the second half of this year, that the tropical cyclone season would be below average. But, of course, it only takes one bad cyclone, so we want people to take care. But, certainly, the odds are reduced."
And not only Australia will feel the effects of the El Nino.
Dr Jones reminds the influence of El Nino is global.
"In our local region, we would expect below average rainfall conditions to affect most of south-east Asia. So, Thailand -- southern parts of Thailand -- through Malaysia, Singapore, Papua New Guinea, Indonesia, we know often have dry conditions in summer, more significant El Nino events cause drought. When we head out towards the Americas, the signal tends to reverse, so coastal parts of South America, up through California into the north-west of the US tend to see above average rainfall conditions."
Farmers of major crops like wheat, soybean, rice and corn in Australia, Asia and South America are expected to be hit by the weather conditions brought on by the El Nino.
