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Scientists measure Amazon drought and deforestation feedback loop: Study

  • Researchers have warned about the Amazon rainforest-to-savanna tipping point for years, but a clearer picture of how this may happen is emerging with new research.
  • A recent study covering the years 2003-2014 in the Amazon basin found that the deforestation-drought feedback loop accounts for 4% of the region’s drought, and 0.13% of deforestation per millimeter of rainfall lost (for example, a rainfall decrease of 200 millimeters would then trigger an additional 26% increase in deforestation).
  • Experts not connected with the study say that the actual percentages could be higher, because Brazilian politics have shifted since 2003-14, leading to major deforestation, while climate change impacts have intensified. The authors agree their results may be underestimated, but say the figures are useful in setting a baseline for climate models.
  • Deforestation and drying in the Amazon could cause the rainforest to spiral into becoming a degraded, dry savanna if nothing is done to deactivate the feedback loop. However, it is difficult to say how soon that tipping point will be reached.
The Amazon has been a stable biome for many centuries. But scientists believe that dryer conditions could bring rapid change to the rainforest, and soon. Image by Rhett A. Butler / Mongabay.

While it is now well accepted that Amazon rainforest deforestation directly contributes to worsening droughts in the region, and vice versa, a recent study published in Environmental Research Letters has attempted to calculate the exact percentages of this knock-on effect for the first time.

A deadly trifecta of deforestation, drought, and escalating global climate change — each impacting the others — threatens to pull the plug on the region’s plentiful precipitation, possibly crashing the biome since the Amazon rainforest depends on its rain cycle to survive and thrive. It’s a phenomenon scientists call a positive feedback loop: deforestation causes drought, which in turn, worsens deforestation, and so on, intensifying the effect.

The study concluded that deforestation causes 4% of drought, while drought accounts for 0.13% of deforestation per millimeter of rain in the Amazon biome. This means that if rainfall in the region decreases by 200 millimeters (7.9 inches), it would then trigger an additional 26% increase in deforestation, according to the findings.

Amazon experts applauded the study’s novelty but also told Mongabay they believed the actual percentages are likely higher and also greatly depend on political decisions going forward.

Climate feedback loops, such as the one illustrated in the recent study, may push the Amazon past its tipping point as deforestation advances, turning the region from wet rainforest into a drier, degraded savanna. Image by Arie Staal.

Deforestation and drought worsening in tandem

Deforestation continues to soar in the Brazilian Amazon, increasing by at least a third since Jair Bolsonaro took office in January 2019. His administration is spearheading the intensive economic exploitation of the rainforest — pushing for reduced enforcement and deregulation, lobbying for more environmentally destructive mining and infrastructure projects on indigenous and conserved lands, and encouraging land grabbing via inflammatory rhetoric.

But even as deforestation roars ahead, with this year forecast to be a very dry fire-prone year, scientists warn that the first signs of permanent drying in the rainforest are already showing: wet-adapted species are starting to die and satellite images show decreased water vapor even in remote parts of the rainforest, far from the so-called Amazon Arc of Deforestation.

These findings, the authors say, raise concern about the future of the forest: as deforestation advances, the feedback loop gets stronger, making it harder over time to reverse the effects. “These results show us how important it is for us to control deforestation and recover the environmental governance in Brazil,” Bernardo Flores, one of the authors and a climate scientist at the University of Campinas in Brazil, told Mongabay.

In Barcelos, Amazonas state, Brazil, the rainforest was burnt, then flooded. Fire is believed to be one of the primary accelerators of the Amazon tipping point. Image by Bernardo Flores.

Numbers too conservative; feedback may be stronger

As the destructive deforestation-drought feedback loop intensifies, the Amazon rainforest as humanity has known it for centuries could soon change forever. Passing a precipitation-reduction tipping point, scientists warn, the forest could transform into a drier, degraded savanna. In the process, the biome would release huge amounts of carbon into the atmosphere, further destabilizing the regional and global climate, while also eliminating thousands of rainforest species.

Until now, no one had attempted to calculate statistically how much deforestation and drought affect one another, and though most scientists agree on the big picture, the study is the first to attribute exact percentages to the feedback loop.

“It’s a step towards better understanding how this [feedback mechanism] works in the Amazon rainforest. It’s important for us to be able to make forecasts for the future,” said Flores, who said the numbers can be plugged into climate models for more accurate predictions and a better understanding of the inner workings of the forest.

Causal loop diagram of the hypothesized drought-deforestation feedback loop in the Amazon. All the steps illustrated in this diagram are analyzed in the study. Image courtesy of Bernardo Flores.

Experts say the intensification of the feedback loop is driven by the fact that deforestation and drought interact to make the Amazon rainforest more flammable for longer. “When it rains less during the rainy season, especially towards the end in March, Abril and May in Southern Amazonia, the climate conditions trigger an earlier start of the deforestation phase,” Carlos Nobre, one of the world’s leading experts on the Amazon tipping point and a senior researcher at the University of São Paulo in Brazil, told Mongabay.

“The deforested areas will become flammable earlier in the year, leading to more fires and the faster preparation of open areas for grazing pastures,” he added. It’s important to note that most fires in the Brazilian Amazon are not natural, but are human-caused to clear land for cattle and crops. Some recorded effects of deforestation, such as the increasing duration of the dry season and growing intensity of heat in dry spells, were not accounted for in the study.

For Nobre, more exactly quantifying feedback mechanisms is key to calculating the temporal scale of the Amazon tipping point — knowing whether it is likely to happen sooner or later. But, he adds, the estimated percentages arrived at in the study are likely higher in light of recent research.

“In areas with high deforestation, shown clearly [in Leite-Filho’s 2019 article], the beginning of the rainy season is delayed by one to two weeks compared to non-deforested areas, and the dry season is drawn out,” Nobre told Mongabay. “When this effect is considered in simulations with realistic earth system models, the relation between deforestation and the increase of drought will be much higher than 4%, due to less water being recycled through vegetation.”

This is a study limitation readily embraced by the authors: “We could not account for all effects of deforestation, so the numbers may be underestimated,” Arie Staal, the paper’s lead author and a researcher at the Stockholm Resilience Center, told Mongabay. For Staal, the figures work as a baseline. “It can be read as at least 4%.”

Brazil President Jair Bolsonaro is pushing large infrastructure projects forward, including the paving of highways that cut through the rainforest. The BR-163 highway, along Brazil’s Arc of Deforestation, is being repaved this year. Paving provides much easier and greater access to the rainforest, which leads to quickening deforestation and drying. Image by Bernardo Flores.

Results may be worse under current government

Brazil was a starkly different nation politically from 2003 to 2014, the years covered by the study. During that period deforestation rates plummeted and Amazon conservation thrived, a shift largely credited to the actions of Marina Silva, Brazil’s Environment Minister from 2003 to 2008.

Over the last five years, this trend reversed: first under the austerity government of Michel Temer, and now under the administration of Jair Bolsonaro. In 2019, deforestation rates skyrocketed, with forest loss exceeding 10,000 square kilometers (3,860 square miles). Deforestation had hit an all-time low of 4,571 square kilometers (1,765 square miles) in 2012.

“Brazil used to be an example of [good] environmental management on the global stage,” Argemiro Leite-Filho, a climate expert at Brazil’s Federal University of Minas Gerais told Mongabay. “This was before the dismantling of environmental organizations, at a time when the Brazilian government still believed in science and its scientists.”

The dramatic shift in Brazilian environmental policy, paired with the extreme droughts of 2005 and 2010, may have made the study data less accurate in the present moment, according to Leite-Filho. Even if the role played by deforestation in the Amazon’s drying was accurately pinpointed over the study period, those percentages may have been pushed significantly higher by evolving politics since 2016 and worsening large-scale climate change in recent years.

For Staal, however, the study stresses the critical role human decisions play in the region. “From global to local scales, all affect whether or not we’re evading a tipping point in the future,” he told Mongabay. “It’s not just an ecological climatic tipping point; humans are a part of those dynamics.”

Citation: Arie Staal, et al. Feedback between drought and deforestation in the Amazon. Environmental Research Letters 15 044024 (2020).

Banner Image: The sun beats down on the Amazon rainforest. Image by Rhett A. Butler / Mongabay.

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