In 2010, the Amazon was facing an intense drought that devastated the rainforest. New results based on lidar and spectral images reignite the eternal debate: does the repetition of droughts harm the rainforest? How can a forest endure climate change?

The 2010 drought in the Amazon was the worst of the last two centuries. Shortages of rainfall have been observed over an area of ​​more than 3 million km². As a result, nearly 1.5 billion tons of CO ₂ were not absorbed by the  rainforest . Already in 2005, an intense drought had occurred on the Amazon basin : 1.9 million km² were then in  shortage of water . This drought, scientists had characterized it as a phenomenon that occurs only once a century.

The Amazon rainforest is a powerful  CO ₂ sensor . His health affects the global climate . The 2010 drought devastated millions of hectares and the atmosphere has undoubtedly warmed. New data analyzes, presented at the meeting of the American Geophysical Union ( AGU meeting ) , suggest that about 4% of trees would have disappeared in areas most affected by water shortages. These analyzes also suggest that satellite data, widely used to measure  water stress in tropical fores

Increased mortality of Amazonian trees in drought zone

The data, collected by  Gregory Asner  of the  Carnegie Institution for Science  in Palo Alto, California, was obtained from an airplane. On board, a lidar and a spectrometer were used to test 500,000 ha of forest between Brazil and Peru. Researchers were able to identify trees individually, determine their health status and accurately measure their size and mass . Gregory Asner’s team carried out a series of measurements on an area of ​​the forest by flying over it at 2,000 m altitude.

The studies began a year and a half before the 2010 drought. Harvesting data over this period quantified tree loss and tree fall. Spectral analyzes identified 21   different chemical signatures , such as the water and pigment content of the leaves. According to their data, 4% of the trees in the drought zone were dead. This is a mortality rate 4 times higher than the average rate in the tropical forest.

The drought in 2010 was preceded by a major drought in 2005, but also by a smaller drought in 2007.  “The whole system is stressed and falling apart,” explains Gregory Asner. The question of the role of previous droughts is debated. Studies after the  2005 drought  showed that photosynthesis was unaffected by the event, suggesting an astonishing resilience of the forest. The data presented by Gregory Asner have not yet been published, but when they are, they will necessarily reopen the debate.

ts, do not sufficiently take into account the impacts of  global warming.