July 7 (Bloomberg) -- Australia, the world's sixth-largest wheat exporter, may experience drought twice as often in the next 20 to 30 years as in the past and effects may be two times as severe, a government report said.

A warmer and drier climate is expected across Australia over the next two to three decades, the Bureau of Meterology and the Commonwealth Scientific and Industrial Research Organization said yesterday in a joint report. Exceptional temperatures may occur once every two years in many key agricultural areas, it said.

About 10 to 12 percent of each region of Australia has had exceptionally hot weather in last 40 years, which is about twice the expected long term average of five percent, the report said. Australia's average annual mean temperature has risen 0.9 percent since 1910 with most of the warming occurring since 1950, it said.

Australia is experiencing the worst drought on record with water-use restrictions having been in place in Sydney for six years. The Murray-Darling Basin river system, home to almost half the nation's farms, is under long-term environmental and ecological degradation as a result of land clearing and water shortages, a government report showed last month.

The nation needs to introduce an emissions trading system to address climate change, Ross Garnaut, the government's adviser on global warming said in a report on July 4.

To contact the reporter on this story: Rebecca Keenan in Melbourne at rkeenan5@bloomberg.net

Last Updated: July 6, 2008 21:36 EDT