By Colin Packham
SYDNEY (Reuters) - Australia's weather bureau said on Tuesday there were clear signs El Nino was developing in the eastern Pacific, raising concerns over the potential impact of the weather event on agriculture at time of soaring global food prices.
El Nino is a periodic warming of the eastern equatorial Pacific Ocean and its arrival comes as fears grow about food prices. Severe drought in the United States has withered the corn crop, sending prices up 60 percent in two months. Soy prices have also jumped after drought in South America.
The weather pattern is normally associated with drier conditions on the east coast of Australia, potentially damaging important export crops such as wheat, which is heavily reliant on rains during the spring to summer period to boost yields.
Australian wheat production is forecast to dip this year from the record 2011/12 season and dry weather across Western Australia has seen forecasts downgraded in recent weeks.
While El Nino poses a risk to east coast production, this may be partly offset in New South Wales state, where Australia's premier grade wheat is grown, by good rains in recent months.
"In New South Wales, the soil moisture going into May was exceptional because of the summer rain, and while there has been some frost, there some areas of New South Wales which don't need another drink," said Andrew Woodhouse, an analyst at brokerage Advance Trading Australasia.
South Australia's wheat crop could face a bigger risk from the drier weather associated with El Nino.
"I have downgraded my South Australia wheat forecast by nearly a million tonnes to 2.86 million tonnes," Woodhouse said, who sees overall wheat output at 22.56 million tons in the current crop year. Australia is forecast to be the world's second-biggest wheat exporter again this year.
EL NINO INTENSITY AND DURATION
The Australian Bureau of Meteorology said although El Nino development stalled in the second half of July, "over the past fortnight indicators such as the Southern Oscillation Index (a gauge of atmospheric pressure) and trade wind strength have shown renewed trends that are consistent with the early stages of an El Nino event."
Japan's weather bureau said on Friday the weather pattern was underway.
However, the Australian weather bureau said it was being "conservative", stressing that its outlook was consistent with the U.S. National Oceanic and Atmospheric Administration, and not at odds with the Japanese weather bureau.
"At the moment, the ocean is looking El Nino-like, but the atmosphere is still not playing ball," Andrew Watkins, climate manager at the Australian Bureau of Meteorology, said.
Australia's climate model predicts a "mild" El Nino, but Watkins warned it was difficult to gauge the impact.
"Most likely the El Nino will be a relatively weak event in the grand scheme. Having said that, weak events have had strong impacts in Australia like 2006/07 was not a particularly strong event but had a strong impact on Australia," Watkins said.
El Nino and its closely related sibling La Nina can cause havoc with global weather by disrupting ocean and atmospheric circulation patterns.
The intense 1997-98 El Nino killed 24,000 people, caused $34 billion in direct losses and triggered drought and fires in Southeast Asia, intense winter storms along the U.S. west coast, floods in East Africa and both floods and drought in China, the U.N.'s World Meteorological Agency says.
During an El Nino, warm waters pile up in the eastern tropical Pacific, leading to the weakening and even reversal of the westerly trade winds. This leads to drier conditions in Southeast Asia and parts of Australia but heavy rains in Peru and California.
The emergence of an El Nino comes just months after the end of the record-breaking La Nina events of 2010-12 that battered parts of the globe, damaging crops, mines and triggering floods.
The big unknown is how intense and how long the developing El Nino phenomenon will be. An intense El Nino can cause widespread drought in Australia, parts of Africa, Southeast Asia and India, but also bring rains to other parts of the globe.
(Additional reporting by David Fogarty in SINGAPORE; Editing by Ed Davies)