Amazon forest may get drier, but survive warming

OSLO Mon Feb 9, 2009 5:44pm EST

A family travels by canoe on the Maranon river in the Pacaya Samiria National Reserve in the Amazon jungle March 28, 2008. REUTERS/Mariana Bazo

A family travels by canoe on the Maranon river in the Pacaya Samiria National Reserve in the Amazon jungle March 28, 2008.

Credit: Reuters/Mariana Bazo

OSLO (Reuters) - Amazonian forests may be less vulnerable to dying off from global warming than feared because many projections underestimate rainfall, a study showed.

The report, by scientists in Britain, said Brazil and other nations in the region would also have to act to help avert any irreversible drying of the eastern Amazon, the region most at risk from climate change, deforestation and fires.

"The rainfall regime in eastern Amazonia is likely to shift over the 21st century in a direction that favors more seasonal forests rather than savannah," they wrote in this week's U.S. Proceedings of the National Academy of Sciences, released on Monday.

Seasonal forests have wet and dry seasons rather than the current rainforest, which is permanently drenched. That shift could favor new species of trees, other plants and animals.

The findings contrast with past projections that the Amazon forest could die and be replaced by savannah.

A 2007 report by the U.N. Climate Panel, which is a snapshot of global warming science by the world's leading experts, said: "By mid-century, increases in temperature and associated decreases in soil water are projected to lead to gradual replacement of tropical forest by savannah in eastern Amazonia."

The new study said that almost all of 19 global climate models underestimated rainfall in the world's biggest tropical forest after the scientists compared the models with observations of 20th century climate.

Lowland forests in the Amazon have annual average rainfall of 2,400 mm (94 inches), it said. Projected cuts in rainfall meant the region would still be wet enough to sustain a forest.

The experts also examined field studies of how the Amazon might react to drying. It said that seasonal forests would be more resilient to the occasional drought but more vulnerable to fires than the current rainforest.

"The fundamental way to minimize the risk of Amazon dieback is to control greenhouse gas emissions globally, particularly from fossil fuel combustion in the developed world and Asia," said Yadvinder Malhi, the lead author from Oxford University.

But he said that governments led by Brazil also needed to manage the forests better.

Global warming is "accompanied by an unprecedented intensity of direct pressure on the tropical forests through logging, deforestation, fragmentation, and fire use," the scientists wrote.

And fires, including those touched off by lightning, were more likely to cause wide damage to forests already fragmented by roads or by farmers clearing land to plant crops such as soya beans.

(Editing by Alison Williams)

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