Rainforest burning in South America can be predicted months in advance using small shifts in ocean temperatures, UC Irvine scientists say in a study to be published Friday.

The findings could one day lead to similar predictions for wildfires in the western United States.

The scientists made surprisingly accurate predictions of the intensity of wildfires in 2010 with their method, which measures temperature shifts as small as a quarter of a degree Celsius in the Atlantic, and one degree in the Pacific, to forecast possible drought conditions in the Amazon three to six months later.

They saw warmer ocean temperatures in 2010 and predicted a spike in wildfire, which later occurred.

"If it is cooler than normal in the North Atlantic or the Pacific, then the fire season doesn't seem to be very severe," said James Randerson, a co-author with lead author Yang Chen of the study being published in the journal, Science. "If it is warmer than usual, it leads to these drought conditions, and you get these larger fires."

The effect is like that of El Niño and La Niña patterns in the equatorial Pacific, which raise or lower ocean temperatures and can affect rainfall on the U.S. West Coast.

"It's very similar in the sense that El Niño can have effects for us that persist after the actual event," Randerson said.

The rate of deforestation has actually dropped in the Brazilian Amazon over the past decade, in part because of efforts to curb it by the Brazilian government, Randerson said.

But while deforestation -- say, from clearcutting for agriculture -- is on the decline, wildfires are not showing a similar drop.

In some areas, Randerson said, fire is still being used to clear land, for example to create pastures for cattle.

"What we think might be going on, in particular during these really dry years, these droughts, is that these fires are escaping and burning into these undisturbed forests," he said.

He hopes land managers might use the method to limit wildfires; the burning of South American forests not only reduces the diversity of lifeforms, but releases large amounts of carbon into the atmosphere, contributing to global warming.

"From the perspective of trying to slow the damage to forests and the loss of carbon, contributing to climate change, it's really important to control the rate of fires," Randerson said.

In coming years, further refinement of the forecasting model could lead to similar predictions in Central Africa, Indonesia, parts of Russia and even the western United States.

In California, he said, "sea-surface temperatures may contribute to snowpack, and may set up a situation that will also have a measurable impact on soil moisture."

But applying the method elsewhere on the planet is a goal for the future. For now, the scientists are concentrating on checking their South American prediction method for 2011-- which so far agrees with early data -- and refining it for 2012 and 2013.