January 20th, 2013 by James Ayre
The Amazon rainforest has been suffering through the effects of a mega-drought, covering an area more than twice the size of California, since 2005, a new NASA-led study has found.
This new research, “when combined with observed recurrences of droughts every few years and associated damage to the forests in southern and western Amazonia in the past decade, suggest these rainforests may be showing the first signs of potential large-scale degradation due to climate change.”
This first-wave of damage caused by climate change is also being greatly exacerbated by human activities such as deforestation and water diversion/groundwater extraction. These activities, themselves, then further contribute to climate change by causing more forest fires and decreased carbon sequestration. Deforestation is currently one of the primary drivers of climate change.
The new research was done by conducting an analysis of over a decades worth of satellite microwave radar data gathered over Amazonia between 2000 and 2009. “The observations included measurements of rainfall from NASA’s Tropical Rainfall Measuring Mission and measurements of the moisture content and structure of the forest canopy (top layer) from the Seawinds scatterometer on NASA’s QuikScat spacecraft.”
What the researchers found was that during “the summer of 2005, more than 270,000 square miles of pristine, old-growth forest in southwestern Amazonia experienced an extensive, severe drought.” This resulted in enormous changes to the forest canopy that even satellites could detect. These changes include: large-scale dieback of branches, and tree falls. The largest and oldest trees seemed to be the ones that were most likely to die. And it’s these trees that are some of the most important in that environment, blanketing the forest, and many of trees, plants, and animals that have evolved to live in its shade.
And even after rainfall levels slowly recovered in the following years, “the damage to the forest canopy persisted all the way to the next major drought, which began in 2010. About half the forest affected by the 2005 drought — an area the size of California — did not recover by the time QuikScat stopped gathering global data in November 2009 and before the start of a more extensive drought in 2010.”
The drought in 2010 covered almost half of the whole Amazon forest. And amazingly, about one fifth of the entire forest was experiencing severe drought
“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, 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.”
These recent mega-droughts in the Amazon have shown just how vulnerable tropical forests are to climate change, especially after you consider how diminished/weakened many of them already are from other factors such as deforestation and water diversion/extraction.
Wildfires also greatly increased during drought years, and especially after the large tree die-offs that followed severe droughts, as both satelitte and ground data have shown. “Until now, there had been no satellite-based assessment of the multi-year impacts of these droughts across all of Amazonia. Large-scale droughts can lead to sustained releases of carbon dioxide from decaying wood, affecting ecosystems and Earth’s carbon cycle.”
Interestingly, according to the researchers, the 2005 drought in the Amazon was caused by the same conditions that lead to Hurricane Katrina, “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,” Saatchi said. “An extreme climate event caused the drought, which subsequently damaged the Amazonian trees.”
Large droughts, such as the 2005 one, have considerable and very long-lasting effects on rain-forests. “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 said. “This may alter the structure and function of Amazonian rainforest ecosystems.”
The situation in the Amazon is unprecedented over the last century (as far back as records go), and when combined with all of the other human factors, the future of the Amazon is looking very dry.
The new research was just published in the Proceedings of the National Academy of Sciences.
Source: NASA/Jet Propulsion Laboratory
Image Credits: NASA/JPL-Caltech/GSFC; Amazon via Wikimedia Commons
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