Damage from megadroughts threaten Amazon rainforest

During the last half century, the seemingly endless Amazon has lost at least 17 percent of its forest cover, according to WWF. Shown here, a burnt Amazon forest.

A new study by an international team of researchers is now showing that over half of the Amazon rainforest has been damaged by two megadroughts, in 2005 and 2010, and points to the climate change vulnerability of this forest that has been called "The Lungs of the Earth".

The researchers, led by Sassan Saatchi, from NASA's Jet Propulsion Laboratory in Pasadena, California, examined more than 10 years' worth of moisture and forest canopy data, from NASA's Tropical Rainfall Measurement Mission (TRMM) and the Seawinds scatterometer on NASA's QuikScat satellite. They found that, although initial estimates put the area affected by the 2005 drought at 700,000 square kilometres, roughly 1.7 million square kilometres (nearly 30% of the Amazon) were actually affected. Also, even though rainfall rates slowly recovered in the years after, the damage caused by the drought persisted right up until a second, more severe drought affected an even wider area of the rainforest starting in 2010.

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"The biggest surprise for us was that the effects appeared to persist for years after the 2005 drought," said Yadvinder Malhi, one of the study co-authors from the Environmental Change Institute at the University of Oxford, UK. "We had expected the forest canopy to bounce back after a year with a new flush of leaf growth, but the damage appeared to persist right up to the subsequent drought in 2010."

This second megadrought, which affected over half of the 5.5 million km² rainforest, caused a 'double-whammy' as it impacted on over half a million km² of the region affected by 2005 drought, causing even more damage to the stressed environment.

According to this research, published in this month's Proceedings of the National Academy of Sciences, it's rising Atlantic sea-surface temperatures — caused by climate change — that are to blame for the 2005 megadrought.

"In effect, the same climate phenomenon that helped form hurricanes Katrina and Rita along U.S. southern coasts in 2005 also likely caused the severe drought in southwest Amazonia," Saatchi said. "An extreme climate event caused the drought, which subsequently damaged the Amazonian trees."

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"Our results suggest that if droughts continue at five- to 10-year intervals or increase in frequency due to climate change, large areas of the Amazon forest are likely to be exposed to persistent effects of droughts and corresponding slow forest recovery," he added. "This may alter the structure and function of Amazonian rainforest ecosystems."