Karmactive Team
Deforestation in the Brazilian Amazon is responsible for approximately 74.5% of the reduction in rainfall and 16.5% of the temperature increase during the dry season, according to a Nature Communications study published September 2, 2025.
The study analyzed long-term atmospheric and land cover change data across 29 areas in the Brazilian Legal Amazon from 1985 to 2020, using parametric statistical models to disentangle the effects of forest loss and alterations of temperature, precipitation, and greenhouse gas mixing ratios.
Over the past 35 years, deforestation has accounted for approximately 74.5% of the ~ 21 mm dry season⁻¹ decline and 16.5% of the 2°C rise in maximum surface air temperature. While the rise in atmospheric methane (CH₄) and carbon dioxide (CO₂) mixing ratios is primarily driven by global emissions (>99%), deforestation has significantly increased surface air temperatures and reduced precipitation during the Amazonian dry season.
Key Study Findings:
| Variable | Total Change (1985-2020) | Deforestation Contribution | Global Climate Contribution |
| Dry season rainfall | -21 mm | -15.8 mm (74.5%) | -5.2 mm (25.5%) |
| Maximum temperature | +2.0°C | +0.39°C (16.5%) | +1.63°C (83.5%) |
| CO₂ mixing ratio | +87 ppm | <1% | >99% |
| CH₄ mixing ratio | +173 ppb | 0.1% | 99.9% |
Source: Franco et al., Nature Communications (2025)
The Flying Rivers Mechanism
Through deep roots and vast leaf area, trees pump water skyward, feeding the “flying rivers” – atmospheric flows that deliver rainfall to the Amazon itself and to far-flung biomes such as the Cerrado. Trees act as water pumps and influence regional circulation through transpiration supplying >40% of Amazon rainfall.
“Several scientific articles on the Amazon have already shown that the temperature is higher, that rainfall has decreased, and that the dry season has increased, but there was still no separation between the effect of climate change, caused mainly by pollution from countries in the Northern Hemisphere, and deforestation caused by Brazil itself. Through this study, we were able to separate and weigh each of these components, practically showing a kind of ‘account payable,'” summarizes Professor Luiz Augusto Toledo Machado, a researcher at the University of São Paulo’s Physics Institute (IF-USP) and a collaborator at the Max Planck Institute’s Department of Chemistry in Germany.
At the end of last year, another study co-authored by USP researchers revealed the physical-chemical mechanisms that drive rain formation in the Amazon. This mechanism involves the production of aerosol nanoparticles, rainfall-induced canopy processes, and chemical reactions at high altitudes between night and day. The result is a kind of aerosol “machine” that produces clouds.
“We were expecting to see deforestation as a driver, but not this much,” said Marco Franco, an assistant professor at the University of São Paulo who led the study. “It tells us a lot about what’s going on in the biome.”
Critical Thresholds Drive Early Impact
The models show the most intense changes in rainfall and temperature occur when 10% to 40% of the forest is removed. “The effects of the changes, especially in temperature and precipitation, are much more significant in the first few percent of deforestation,” said co-author Marco Aurélio Franco from USP’s Institute of Astronomy, Geophysics, and Atmospheric Sciences.
Research has shown that the impact of deforestation is most intense in the early stages. The greatest changes in the local climate occur when 10% to 40% of the forest is lost.
In the most heavily cleared areas, maximum temperatures rose by more than 1.2°C due to deforestation alone, while rainfall fell by more than 50mm during the dry season. “In other words, we have to preserve the forest; that’s very clear. We can’t transform it into something else, such as pastureland. If there’s any type of exploitation, it needs to be sustainable,” Franco said.
Franco is the first author of the article and received a postdoctoral fellowship from FAPESP, which also supported the work through another grant (21/12954-5) from the Research Center for Greenhouse Gas Innovation (20/15230-5) and the Research Program on Global Climate Change – RPGCC (22/07974-0).
The project supported by the RPGCC is being developed in partnership with the Chinese Academy of Sciences. One of the overseas leaders and authors of the work is researcher Xiyan Xu.
Record Fire Losses in 2024
Current monitoring data reveals the problem intensifying. In 2024, the Brazilian Amazon lost 954,126 hectares (2.4 million acres) of primary forest to deforestation. Although this total marked a 13.6% increase from 2023, it was historically relatively low (16th highest overall since 2002). The bigger story is that fires directly impacted an additional 1.9 million hectares (4.6 million acres). This fire impact was the highest on record, surpassing the previous high of 2016 (1.6 million hectares).
Fire hotspots were also located in the northern state Roraima, and along the other major road networks, especially road BR-230 (Trans-Amazonian Highway) in the states of Pará and Amazonas, and road BR-364 in the state of Acre. Previous research has revealed that over 70% of major fires in the Brazilian Amazon are burning recently deforested areas.
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According to data from MapBiomas, a collaborative network formed by non-governmental organizations, universities, and technology startups that maps land cover and land use in Brazil, the Brazilian Amazon lost 14% of its native vegetation between 1985 and 2023, reaching an area of 553,000 km²—equivalent to the territory of France. Pasture conversion was the main cause during this period.
Monitoring Systems Track Real-Time Change
Despite deforestation reaching its second lowest level between August 2024 and July 2025—an area of 4,495 km²—containing degradation, especially that caused by fire, remains challenging. Brazil’s National Institute for Space Research (INPE) operates the DETER system for near real-time detection and PRODES for annual assessments.
The dry season, which occurs between June and November, is when the effects of deforestation are most noticeable, particularly on rainfall. The cumulative effects further intensify seasonality.
To reach their conclusions, the scientists used parametric surface equations that considered both annual variations and deforestation. These equations enabled them to distinguish the unique contributions of global climate change and vegetation loss. They also used remote sensing data sets and long-term reanalyses, including land use classifications produced by MapBiomas.
Amazon Conservation’s Monitoring of the Andes Amazon Program (MAAP) reports on the most urgent threats across the Amazon in real-time with technology. MAAP provides vital technical information in an easy-to-understand format for policymakers, law enforcement, civil society, researchers, the media, and the general public to help decipher what is happening in the Amazon and drive action against illegal deforestation.
Projections Point to Drier Future
If current deforestation trends persist, by 2035 the region could lose another 7mm of rainfall in the dry season and heat up by 0.6°C, pushing the Amazon toward a drier climate like the Cerrado or Caatinga. Such a shift would test the resilience of the forest’s more than 11,000 known tree species and the communities who rely on them. It could also weaken rainfall over distant agricultural zones that depend on the Amazon’s “flying rivers,” with implications for food production across much of South America.
The researchers warn in the article that if deforestation continues unchecked, then extrapolation of the results suggests a further decline in total precipitation during the dry season and an even greater rise in temperature.
Recent studies indicate that deforestation in the Amazon is altering South American monsoon patterns, which bring abundant rainfall to central and southeastern Brazil during the summer. These altered patterns result in drier conditions that could compromise the long-term resilience of the forest. Extreme events, such as the 2023 and 2024 droughts, only exacerbate the situation.
Studies also suggest that deforestation is altering the South American monsoon, increasing the risk of drought in central and southeastern Brazil. The Amazon endured record dry spells in 2023 and 2024, disrupting river transport and straining hydropower.
The research comes as Brazil prepares to host COP30 in Belém next November, placing Amazon conservation at the center of global climate negotiations.
Methods Summary: The authors analysed atmospheric and land-cover data across 29 subareas of the Brazilian Legal Amazon (1985–2020) and used statistical models to separate local land-use effects from global greenhouse-gas influences.
The study was discussed across multiple research areas including deforestation patterns, rainfall changes, temperature increases, and greenhouse gas mixing ratios during the Amazon dry season period. The research examined the interaction between regional land-use changes and global climate factors in transforming Amazon climate conditions.
The article “How climate change and deforestation interact in the transformation of the Amazon rainforest” can be read at www.nature.com/articles/s41467-025-63156-0.
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