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Barrage of droughts weakens Amazon’s capacity to bounce back, study finds

Credits: NASA/JPL-Caltech

  • In the last two decades, the Amazon Rainforest has been impacted by increasingly intense and frequent droughts, the most severe occurring in 2005, 2010 and 2015.
  • A new study shows that stretches of forest affected by drought have taken between one and three years to recover their growth rate.
  • With droughts expected to worsen because of global warming, scientists warn that the Amazon’s capacity for carbon absorption will be increasingly compromised.
  • They highlight that efforts to stabilize the climate will depend on combating deforestation in the Amazon.

Severe droughts over the past two decades have affected the resilience of the Amazon Rainforest, a new study shows, with stretches of affected forest taking between one and three years to recover their usual growth rate.

The work by researchers from Brazil and Portugal focused on an analysis of primary productivity — the amount of organic matter produced by vegetation, which is a parameter commonly used to assess an ecosystem’s capacity for regeneration. In drought situations, the process of plants absorbing carbon dioxide to produce oxygen tends to take longer.

According to the study, the impacts were particularly severe during the droughts of 2005, 2010 and 2015, considered the worst of the century and a warning that events like these are becoming more frequent, now five years apart.

The findings showed that carbon absorption during the period of recuperation after a drought was 13% lower than levels prior to the drought or in tracts of forest that were not affected by drought.

“We see that in 2005, 2010 and 2015, there was an increase in the deficit in the forest’s resilience,” said lead author Fausto Machado-Silva, a biologist at Fluminense Federal University (UFF).

“The more intense and ample the drought, the greater the debt for the forest to recover,” he said. “Our work shows that the deficit in resilience can increase in two scenarios: due to a greater intensity of drought, as in 2010, when the drop was greater, or because of an extension in the recuperation process, as in 2015.”

According to Machado-Silva, the results are concerning, especially because global warming threatens to hit the Amazon particularly hard. “The scenarios in the IPCC [Intergovernmental Panel on Climate Change] show that we’re going to have an increase in temperature in the Amazon around three to four times the average warming of the planet,” he said.

He added the situation is even more critical considering the rising trend of deforestation in the region, a problem that is itself driving changes in precipitation levels and the forest’s capacity to retain carbon. “The current scenario is causing interference in the hydrological cycle. More portions of deforested land mean less water being returned to the atmosphere,” Machado-Silva said.

Drought conditions on the Rio Negro in 2015. Image courtesy of Amazonas Civil Defense.

Amazon’s role as carbon sink in jeopardy

Climatologist Jose Marengo, general coordinator of research and development at Brazil’s National Center for Natural Disaster Monitoring and Alerts (Cemaden), told Mongabay that while previous studies showed a decline in forest productivity during droughts, the new survey indicates a tendency for this parameter to be reduced in post-drought years. This, said Marengo, who was not involved in the new study, raises questions about “whether forests are in fact resilient.”

The forest “may have been [resilient] in the 20th century, but in the 21st century droughts changed this figure and forests have low resilience in a scenario of more intense and frequent droughts on an increasingly hot planet,” Marengo added.

In a “hypothetical scenario, but one that has not been ruled out,” in the face of unfavorable environmental conditions, Marengo said “the forest could collapse, affecting the regional and global climate.” Considering the risks associated with the loss of resilience in the world’s largest tropical forest, he said: “We have to eliminate deforestation, reduce greenhouse gas emissions, limit agribusiness on Amazonian lands, and protect the forest that is more valuable standing than it is cut down.”

Luiz Aragão, a researcher at Brazil’s National Institute for Space Research (INPE), told Mongabay that in addition to bringing new nuances, such as post-drought scenarios of compromised productivity, the recent study reinforces a number of messages already disseminated in specialized literature on the subject. “We running a great risk of the Amazon Rainforest losing its capacity to contribute as a carbon sink,” said Aragão, who was not involved in the study.

Considering the Amazon’s central role in balancing the climate of the region and the globe, he said the results of the study are important for Brazil’s environmental management.

“There is no justification for removing native vegetation,” Aragão said. “The forest acts as a regulator of the climate and it sustains productive areas that are important to the national economy.”

Citation:

Machado‐Silva, F., Peres, L. F., Gouveia, C. M., Enrich‐Prast, A., Peixoto, R. B., Pereira, J. M., … Libonati, R. (2021). Drought resilience debt drives NPP decline in the Amazon Forest. Global Biogeochemical Cycles35(9). doi:10.1029/2021gb007004

 
This story was reported by Mongabay’s Brazil team and first published here on our Brazil site on Nov. 25, 2021.