More droughts are coming and the Amazon can’t keep up: study

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  • Up to 50% of rainfall in the Amazon comes from the forest itself, as moisture is recycled from the trees to the atmosphere.
  • During severe droughts, when the forest loses more water through evaporation than it receives from rain, trees begin to die. For every three trees that die due to drought in the Amazon rainforest, a fourth tree, even if not directly affected by drought, will also die, according to a new study.
  • As trees disappear and forest dries out, parts of the Amazon will quickly approach a tipping point, where they will turn into a degraded savanna-like ecosystem with few or no trees. .
  • The south and southeast of the Amazon are the regions most vulnerable to tipping. Here, deforestation and fires are most extreme, largely due to cattle ranching and soybean cultivation.

The largest rainforest in the world makes its own weather. Up to half of all precipitation in the Amazon comes from the forest itself, as moisture is recycled from the trees to the atmosphere and vice versa. So what happens when droughts become more severe and less rain enters the system?

For every three trees that die due to drought in the Amazon rainforest, a fourth tree, even if not directly affected by the drought, will also die, according to a new study published in the Proceedings of the National Academy of Sciences. Each part of the forest is interconnected, which means that damage in one area can affect neighboring areas, increasing the negative effects by a third.

“We are studying what would actually happen to the Amazon rainforest if droughts become more frequent in the future, and that is indeed what is assumed with climate change,” study co-author and researcher Nico Wunderling at the Potsdam Institute for Climate Impact Research, says Mongabay.

Scientists to predict that if we continue to burn fossil fuels on a business-as-usual trajectory, the Amazon will experience a nine-in-10-year major drought by 2060.

According to experts, as the forest dries out, parts of it are rapidly approaching a tipping point where they will turn into a degraded savanna-like ecosystem with few or no trees. But rather than viewing the Amazon rainforest as “one big tipping point that will vanish from Earth beyond a certain threshold,” Wunderling said, it’s worth noting that some regions are much more vulnerable to tipping than others. other regions.

Wunderling and his colleagues found that the southern Amazon is the most vulnerable region, the southeast in particular. Here, deforestation is at its peak along the infamous “arc of deforestation,” driven largely by cattle ranching and soybean cultivation.

The map shows the average tipping probability (vulnerability) over the Amazon. The southeastern region is more vulnerable than other regions, but the southern and southwestern regions are also affected. Number of Wunderling et al 2022.

They also found that the severity of the droughts was significant. “Droughts that get too severe lead to tipping,” Wunderling said. In severe drought, the forest loses more water through evaporation than it receives from rain, and trees begin to die.

Not all trees have the same effect on the forest. When trees die or are cut down in the east, it can have a bigger cascading effect on the weather.

It all begins, as most natural systems do, with the sun, which warms the surface waters of the Atlantic Ocean and causes steam to rise and clouds to form. These clouds then carry the rain eastward into the Amazon. The forest absorbs rain and then releases water vapor into the atmosphere through the transpiration of lush vegetation. Known as the “flying rivers” of the Amazon, this mass of water vapor is carried by the westerly windscontributing up to 50% of rainfall in the region.

With fewer trees in the east to recycle moisture from drought and deforestation, the rest of the Amazon is also getting drier. “Lack of moisture recycling in parts of the forest can spread downwind…resulting in about a third of all tipping events,” the paper says.

This map shows the atmospheric moisture recycling network, with blue arrows representing the direction of moisture flux from the Atlantic Ocean through the Amazon in 2014. Figure from Wunderling et al 2022.
The map shows continued deforestation along the southern arc of deforestation in 2021 (from September). UMD/GLAD, ACA/MAAP data. Image via Monitoring of the Andean Amazon Project (MAAP).

To arrive at these conclusions, the team used a technique called network analysis, dividing a map of the rainforest into 600 sections to see how drought conditions in one area would affect others.

They looked at past measurements such as rainfall and transpiration rates for each section and assumed that the trees there would be adapted to those local conditions. For example, the central Amazon rainforest is adapted to more rain, while southern regions have adapted to drier conditions with deeper-rooted trees and more drought-resistant species.

Yet despite these adaptations, southern forests are not equipped to withstand long periods without water. “So we find that even the dry-season-adapted parts of the Amazon rainforest will not necessarily survive a new climate normal and the risk of tipping over into savannah or having no trees at all is high,” co- Study author Boris Sakschewski, also of the Potsdam Institute, said in a statement.

“The consequences for biodiversity would be disastrous, but so would the local, regional and global climate,” he added.

Macaws fly over the rainforests of Peru.
Macaws fly over the rainforests of Peru. Image by Rhett A. Butler/Mongabay.

Carlos Nobre, one of Brazil’s top climatologists and a researcher at the University of São Paulo, who was not involved in the study, said the research is “a good way to show the sensitivity of the south and the south -eastern Amazon, which are highly vulnerable,” and that these findings are consistent with other research.

Not only is the dry season getting longer, Nobre said, but it is also getting drier. “Drought, as we saw in 2005 and 2010, could become the norm,” he said. “The risk of tipping over is very real.”

He noted that the study does not take into account forest degradation, fires or land use change, which “occur enormously throughout the southern Amazon… With these included, the risks [of reaching a tipping point]get even bigger.

Early signs of more permanent drying out in the rainforest are already being felt, scientists warn. Species adapted to humid conditions are start dyingand satellite images To display a decrease in water vapor on remote parts of the rainforest, far from the arc of deforestation.

A strip of Amazon rainforest has been burned in the indigenous territory of Cachoeira Seca.
A swathe of Amazon rainforest has been burned down in the indigenous territory of Cachoeira Seca in the state of Pará, Brazil. Being a legally protected reserve hasn’t stopped it from being targeted by land grabbers and illegal loggers. Image © Daniel Beltra/Greenpeace.

“[W]Although we have studied the impact of drought, this rule also applies to deforestation,” Wunderling said in a statement. “It basically means that when you cut down an acre of forest, what you’re actually destroying is 1.3 acres.”

Since 2019, under the administration of President Jair Bolsonaro, an area of ​​the Brazilian Amazon rainforest larger than Belgium has been destroyed. This year alone, rainforest clearing detected in the Brazilian Amazon exceeded 7,135 square kilometers (2,755 square miles) – the highest on record since 2008 – according to the Brazilian space agency’s Deforestation Alert System. .

Droughts in the Amazon are symptoms of deforestation and climate change. That means we not only have to end deforestation, but we also have to meet the goals of the Paris Agreement, Nobre said. This calls on countries to cut carbon emissions to limit warming to well below 2° Celsius (3.6° Fahrenheit) above pre-industrial levels by 2030. A recent study estimates a 0.1% chance that nations will achieve the goals of the Paris Agreement, unless rapid and dramatic action is taken.

“If we don’t reduce emissions,” Nobre said, “even if we get to zero deforestation, most of the forest will disappear.”

Quote:

Wunderling, N., Staal, A., Sakschewski, B., Hirota, M., Tuinenburg, OA, Donges, JF, … Winkelmann, R. (2022). Recurrent droughts increase the risk of cascading tipping events by overwhelming adaptive capacities in the Amazon rainforest. Proceedings of the National Academy of Sciences, 119(32), e2120777119. do I:10.1073/pnas.2120777119

Esquivel-Muelbert, A., Baker, TR, Dexter, KG, Lewis, SL, Brienen, RJ, Feldpausch, TR, … Phillips, OL (2019). Compositional response of Amazonian forests to climate change. Biology of global change, 25(1), 39-56. do I:10.1111/gcb.14413

Barkhordarian, A., Saatchi, SS, Behrangi, A., Loikith, PC and Mechoso, CR (2019). A recent systematic increase in vapor pressure deficit over tropical South America. Scientific reports, 9(1), 15331. doi:10.1038/s41598-019-51857-8

Vargas Zeppetello, LR, Raftery, AE, & Battisti, DS (2022). Probabilistic projections of increased heat stress due to climate change. Earth & Environment Communications, 3(1), 183. doi:10.1038/s43247-022-00524-4

Banner image: Deforestation and fire in the municipality of Lábrea, located in the north of the state of Amazonas, Brazil in 2021. Image © Christian Braga/Greenpeace.

Liz Kimbrough is a writer for Mongabay. Find her on Twitter: @lizkimbrough_

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