A study led by NASA has found that an area of the Amazon twice the size of California is suffering from the effects of a "megadrought" that began in 2005. Researchers concluded that the results, along with observed recurrences of droughts every few years and associated forest damage, suggests the rainforests "may be showing the first signs of potential large-scale degradation due to climate change."
The scientists found that during the summer of 2005, more than 270,000 square miles (700,000 square kilometers, or 70 million hectares) of pristine, old-growth forest in southwestern Amazonia experienced an extensive, severe drought that caused widespread changes to the forest canopy that were detectable by satellite. Although rainfall levels gradually recovered in subsequent years, the damage to the forest canopy persisted to the next major drought, which began in 2010.
"The biggest surprise for us was that the effects appeared to persist for years after the 2005 drought," said study co-author Yadvinder Malhi of the University of Oxford in the United Kingdom. "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."
The researchers attribute the 2005 Amazonian drought to the long-term warming of tropical Atlantic sea surface temperatures. "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," said research team leader Sassan Saatchi of NASA's Jet Propulsion Laboratory in Pasadena, Calif. "An extreme climate event caused the drought, which subsequently damaged the Amazonian trees."
NASA reports that the drought rate in Amazonia during the past decade is unprecedented over the past century. Observations from ground stations show that rainfall over the southern Amazon rainforest declined by almost 3.2 percent per year in the period from 1970 to 1998.
Photo credit: NASA/JPL-Caltech
