- The Amazon’s “tipping point” refers to the transition of the rainforest into a drier, savanna ecosystem. The rainforest’s ecological balance depends on the transport and recycling of moisture, but deforestation has been shown to disrupt the region’s water cycle.
- Moisture moves east to west, from the Atlantic Ocean across the Amazon Basin via what scientists call “aerial” or “flying rivers,” a critical mechanism in the region’s water cycle.
- A new report from Amazon Conservation’s Monitoring of the Andes Amazon Project identified areas of deforestation that disrupt these flying rivers from hundreds of miles away. It also found that not all parts of the Amazon have the same tipping point.
- The researchers stressed the need for regional, transboundary conservation efforts that account for varied threats in different parts of the Amazon.
Experts often warn about the “tipping point” for the Amazon, a scenario in which the rainforest collapses into a drier, less biodiverse savanna ecosystem. But the term “tipping point” is sometimes misunderstood or generalized, some experts say, suggesting that there will be an instant change to the biome from one day to the next.
In reality, the transition from rainforest to savanna won’t be a single incident, but rather a gradual process happening at different rates across the region, multiple studies show. Some conservationists say there’s still a fundamental confusion within the general public about what the “tipping point” would look like, and what can be done about it.
“For the most part, if you’re reading about the tipping point, you’re left with the impression that it’s like a single event, and that when the Amazon reaches that tipping point, it’s going to go from rainforest to savanna,” Matt Finer, director and senior research specialist of Amazon Conservation’s Monitoring of the Andes Amazon Project (MAAP), told Mongabay. “Very rarely do you get the nuance that it’s much more complicated than that.”
The MAAP team wanted to clarify the way the Amazon tipping point works, and to explain the science to a general readership who might not have access to the latest research. The team combined numerous studies to create a series of maps, revealing that not all parts of the Amazon have the same risk level.
One of the main factors influencing the tipping point is how water moves within the rainforest ecosystem.
Moisture in the Amazon travels from east to west, originating in the Atlantic Ocean and recycling several times through evapotranspiration, a process in which plants release vapor into the atmosphere. The movement of moisture across the rainforest is known as a “flying river” (or “aerial river”), and in some cases is the primary water source for huge swaths of the western Amazon that sit farther from the coast.
At least 75% of rainfall gets recycled in the Amazon, according to one study. It can go through between five or six cycles before air currents hit the Andes and turn southward.
Deforestation interrupts that process, leaving the downwind forest without the recycled moisture it needs to survive. When the forest is cleared, more than 50% of the water runs off instead of being recycled, the same study found. Less moisture means a higher probability of turning into a savanna ecosystem, it said.
As much as 27% of the Amazon could become partial savanna ecosystems by 2050, and as much as 6% could become completely stable savanna, according to one study, which noted that tree mortality has risen in recent years and drought-affiliated species have started to replace them.
“In the distant past, we used to have one severe drought every two decades,” said Carlos Nobre, Professor of Climate and Sustainability at the University of São Paulo. “Now we have had four very severe droughts…we have four severe droughts in twenty years.”
Southern Peru and northern Bolivia are especially dependent on recycled moisture, putting them at higher risk than other parts of the Amazon, the MAAP project found.
Flying rivers look relatively intact during the wet seasons of January and February, passing uninterrupted over the rainforest, according to the MAAP report. But scientists have detected significant disruptions in the dry seasons of July and August. During that time, the cycles shift farther south, hitting stretches of deforestation that interrupt the transfer of moisture and result in less rain in Peru and Bolivia.
“Bluntly put, the Amazon not only cannot withstand further deforestation but also now requires rebuilding as the underpinning base of the hydrological cycle,” a 2019 editorial on the region’s tipping point warned.
The interruptions will only grow as deforestation spreads, the MAAP report said, noting that the expansion of road networks poses an especially serious threat. A proposed federal highway in Brazil, BR-319, would create new deforestation fronts farther north, potentially blocking other flying rivers from reaching the western Amazon, it said.
The project is so concerning to conservationists that some have deemed it the Amazon’s “tipping point road.”
The MAAP report said there needs to be reduced deforestation in the eastern Amazon and new strategic restoration projects to address moisture recycling pathways. It also called for a more regional, transboundary approach to protecting the Amazon, with an understanding that deforestation in one part of the rainforest can do permanent damage to other parts hundreds of miles away.
“You can have conservation initiatives in Peru, Bolivia, Ecuador, Colombia, but if Brazil’s forest gets annihilated, in the long term, these forests could be doomed,” Finer said. “They really depend on their eastern neighbors, which is a fascinating new interconnectedness.”
Banner image: Aerial view of the Amazon Rainforest, near Manaus, Brazil. Image courtesy of Neil Palmer/CIAT. CC BY-NC-ND 2.0
Citations:
Flores, B. M., & Holmgren, M. (2021). White-sand savannas expand at the core of the Amazon after forest wildfires. Ecosystems, 24(7), 1624-1637. doi:10.1007/s10021-021-00607-x
Lovejoy, T. E., & Nobre, C. (2018). Amazon tipping point. Science Advances, 4(2). doi:10.1126/sciadv.aat2340
Lovejoy, T. E., & Nobre, C. (2019). Amazon tipping point: Last chance for action. Science Advances, 5(12). doi:10.1126/sciadv.aba2949
Flores, B. M., Montoya, E., Sakschewski, B., Nascimento, N., Staal, A., Betts, R. A., … Hirota, M. (2024). Critical transitions in the Amazon forest system. Nature, 626(7999), 555-564. doi:10.1038/s41586-023-06970-0
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