A Little Deforestation Can Significantly Alter the Climate: The Mechanism by Which Deforestation Stops Rain in the Amazon - The Truth of the Amazon Dry Season: Rain -74%, Temperature +16%

Visualizing the Disappearing Rainforest by Numbers

The Amazon is the largest tropical forest on Earth, creating "flying rivers" (massive atmospheric waterways) that nourish South America's weather and agriculture. Its heart is drying up. The latest peer-reviewed research has clearly presented a "balance sheet" by accounting for the "culprits" of dry season rain shortages and heat, dividing them into global warming and deforestation.

Analyzing long-term data from 29 regions of the Brazilian Legal Amazon from 1985 to 2020 using a parametric statistical model, it was determined that——74.5% of the dry season rainfall reduction was attributed to deforestation, and 16.5% of the increase in daily maximum temperatures was also attributed to deforestation. Overall, dry season rain has decreased by about 21mm per year, with approximately 15.8mm directly linked to forest loss. While global warming contributes to the remaining decrease, deforestation is identified as the "main culprit" severely damaging the dry season's water cycle. dx.doi.org

The study combined data from ERA5 (temperature), GPM (precipitation), AIRS (CH₄), OCO-2 (CO₂), and MapBiomas (land cover), presenting a depiction that aligns with field observations: the reduction in forest cover has a logarithmic effect, while the impact of time progression (global warming) is almost linear. Furthermore, over 99% of the increase in CH₄ and CO₂ mixing ratios is explained by global emissions, while local temperature and precipitation are sensitive to land use changes, presenting a clear two-layer structure. dx.doi.org

The Severity of the "First 40%"

Notably, the impact becomes significantly larger from the stage of small-scale deforestation. During the initial phase when forest loss reaches 10-40%, the blow to precipitation and temperature is the strongest. In other words, it's not "dangerous because more than half has been cut," but rather "it's already dangerous once a little cutting starts." This non-linearity aligns with the mechanism where the connected system of forest→soil→atmosphere rapidly loses its "cloud-making power" through aerosol generation and convection. phys.org

Dry Seasons Becoming Longer, Hotter, and More Prone to Fires

In the Amazon, the impact of deforestation becomes more apparent during the **dry season (June to November)**. As rain decreases, transpiration weakens, the surface dries, and the fire season extends. Recent large-scale droughts (2023-2024) have dramatically highlighted this trend. Furthermore, the pattern of the South American monsoon is also disrupted, threatening to alter summer rainfall in central and southern Brazil. The research team warns that if deforestation continues, dry season precipitation will further decrease, and temperatures will rise even more. phys.org

Background Statistics: From 1985 to 2023, approximately 14% (553,000 km²) of the Amazon's primary vegetation has been lost. Recently, the deforested area from August 2024 to July 2025 was controlled at 4,495 km², but controlling **"degradation"** due to fires and other factors remains a challenge. phys.org

When the "Flying River" Weakens, Agriculture and Cities Suffer

Forests absorb water through their roots and return it to the atmosphere through their leaves, providing rain to Brazil's inland savanna ecosystems, Cerrado, and agricultural areas through large-scale water vapor transport (flying rivers). The weakening of the flying river can amplify droughts, heatwaves, and fires in the grain belt in a chain reaction. This is consistent with previous research and reports pointing to monsoon disturbances, and the decline in the Amazon's resilience can ripple from regional to global scales. phys.orgThe Guardian

Key Points of the Research Method: Sorting Out Causality

The crux of this study is the use of a statistical model incorporating both "time trends (global warming)" and "reduction in forest cover (regional factors)" to estimate the contribution distribution of dry season temperature, precipitation, and greenhouse gas concentrations. The breakdown shows that of the total precipitation decrease (about 21mm/dry season), deforestation accounts for about 15.8mm, and global warming for about 5.2mm, providing a concrete numerical basis for discussion. dx.doi.org

"Cannot Be Explained by Global Warming Alone" - Field Sense

In the Amazon, over the past few decades, temperatures have risen by about 0.15°C per decade, and the dry season has extended by 6.5 days per decade. However, regions where the decline in dry season precipitation and heat are particularly pronounced overlap with the deforestation frontier. The results of this study support the image painted by local observations and satellite mosaics that "land use changes disrupt the balance of water and heat." dx.doi.org

Voices from the Field and Reactions on Social Media

Immediately after the paper's publication, Nature Communications and Springer Nature's official accounts shared it, and the headline **"About 3/4 of Dry Season Rainfall is Due to Deforestation" was quickly shared on X (formerly Twitter)**. Climate communicators and researchers also commented, "Even early-stage deforestation has a significant impact" and "Policies need to simultaneously pursue 'zero deforestation + degradation countermeasures'." Here are the main points (summary, opinions in posts are those of the individual authors):

• Visualization Effect of the Research: There is a welcoming voice that simple percentage displays accelerate policy discussions (such as in Springer Nature's post). X (formerly Twitter)

• Urgency of the Crisis: ClimateBen and others emphasize the point that "even a little deforestation significantly reduces rain," advocating for an early halt to deforestation. X (formerly Twitter)

• Researchers Sharing: Paleoanthropologist Chris Stringer and ecologists shared the paper link, sparking discussions even outside their fields. X (formerly Twitter)

• Support from Explanatory Articles: Mongabay explained in simple terms for the general public that "the main cause of dry season rainfall reduction is deforestation," also pointing out the policy context (COP30, Belém). news.mongabay.com

• Platforms for Dissemination: Articles from Phys.org and FAPESP press were also shared, creating threads on Facebook and Reddit. phys.orgFacebookReddit

Policy Focus: What to Decide Before COP30 (Belém)

The study is directly linked to the agenda of **COP30 (November 2025, Belém). The figures **"Dry Season Rain -74%, Temperature +16%" demand immediate measures to eradicate illegal logging, curb forest degradation, and manage fires. As long-term data from MapBiomas shows, even if deforestation stabilizes, degradation can expand. Not only zero deforestation, but also investments in **protecting ecosystem quality (restoration, monitoring, local livelihoods)** are crucial. phys.org

Signals to Industry and Finance

• Agriculture and Water Resources: The weakening of flying rivers affects grains, livestock, and hydropower. The loss of 21mm/season of dry season precipitation, when accumulated, directly impacts reservoir levels, river flows, and transportation. dx.doi.org

• Transition Finance: Forest-related risks are incorporated into supply chains, insurance, and government bonds. Companies should return natural capital of forests and soils##