January 31, 2008

 

Australia's main wheat producing state to receive average rainfall until October

 

 

Wheat lands in Western Australia - a major area supplying the global market - face at least average rains through to October when the annual harvest usually begins, according to an outlook issued Thursday (January 31, 2008) by the state's Department of Agriculture & Food.

 

The state accounts for almost 10 percent of the world's traded wheat and accounts for about 38 percent of national wheat output.

 

Most of 12 commonly used climate forecasting models indicate continued La Nina patterns in Pacific Ocean temperatures, before a return to neutral conditions by mid to late 2008, said Department researcher David Stephens.

 

The department's climate indices also indicate a similar, but more extended cooling in the Pacific Ocean with a high chance of weak La Nina conditions persisting until the end of 2008, he said in a statement.

 

In terms of the state's wheatbelt rainfall, this is "indicative of average to above-average rainfall over the next three months and average rainfall is most likely between May and October," he said.

 

Wheat production in the state peaked in 2002-03 at 11.0 million tonnes - about 10 percent of global traded wheat - with more than 90% available for export.

 

The state's wheat output from the past two crops has fallen well below a long-term annual average of 8.2 million tonnes a year under the influence of dry weather.

 

Stephens warned that though La Nina is normally associated with good rainfall in Australia, there is considerable variation on this in Western Australia - as was seen in 2007 when weak, slowly-developing La Nina conditions were recorded.

 

The "great lesson" for the past two years is that a reduced sea surface temperatures (SST) gradient, going from warm in the south Indian Ocean to cold near Indonesia to the northwest of Australia, is negatively related to growing season rainfall in the state's wheatbelt, especially in northern areas, he said.

 

In both 2006 and 2007 a reduced SST gradient developed late in autumn-early winter and this contributed to stronger highs, reduced tropical moisture inflow and drought conditions, he said.

 

"These changes close to the start of the season make long-range forecasting more difficult," he said.

 

While the department's indices currently suggest more positive outlook exists for the 2008 growing season, confidence in this assessment will be enhanced if a La Nina pattern continues. Sea surface temperatures remained warm northwest of Australia and more normal cold frontal activity appears in autumn, he said.

 

Recent trends in broad-scale climate indicators suggest La Nina conditions of moderate strength are in the process of peaking, he said.

 

After a dry May-September period in 2007, there has been a widespread fall in barometric pressure across the Australian continent and rainfall has picked up in recent months.

 

For the first time in seven years, much below-normal pressures were being recorded at Darwin and this has been associated with cyclonic activity, heavy rains and flooding in northeast Australia, he said.