Deforestation in the Brazilian Amazon is doing far more than clearing trees: it’s directly shrinking the region’s rain supply and nudging temperatures upward during the dry season. 

A new study led by scientists at the University of São Paulo (USP) is the first to put hard numbers on how much of the recent shift is due to local forest loss versus global climate change.

The researchers found that deforestation accounts for roughly 74.5% of the observed decline in dry-season rainfall and 16.5% of the warming in the biome.

This work arrives just ahead of COP30 in Belém, the Amazonian capital hosting November’s U.N. climate summit – timing that highlights its policy relevance.

Amazon dry season and deforestation

The team used parametric statistical models to disentangle overlapping influences – forest loss, temperature trends, precipitation shifts, and greenhouse gas concentrations – on the Amazon’s climate. 

On average across the biome, dry-season rainfall has fallen by about 21 millimeters per year, with 15.8 mm of that drop traced to deforestation alone. Meanwhile, maximum temperatures have climbed about 2.0°C, and the researchers attribute 16.5% of that rise to forest clearing, with the remainder tied to global warming.

“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,” said study senior author Luiz Augusto Toledo Machado of USP.

“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.’”

Intense changes from forest loss

One practical insight leaps off the page: the biggest local climate swings happen at the earliest stages of forest loss. 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. 

“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.”

That finding reframes “small” incursions: early clearing is not a harmless nibble – it’s when the local water and heat balance is most sensitive.

A forest that makes its own rain

The Amazon is more than a carbon storehouse; it manufactures its own moisture. 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.

Recent research by some of the same USP scientists illuminated the biome’s rain-making chemistry: aerosol nanoparticles, electrical discharges, and day-night reactions act like a cloud-building “machine.”

Strip away trees, and you weaken that system – less evapotranspiration, fewer cloud seeds, and a longer, harsher dry season primed for fire.

Those dynamics are not abstract. MapBiomas data show the Brazilian Amazon lost 14% of its native vegetation between 1985 and 2023. An area of 553,000 square kilometers, roughly the size of France, was primarily lost to pasture.

Deforestation dropped to its second-lowest level between August 2024 and July 2025 (4,495 km²). However, degradation – especially from fire – remains stubborn and widespread.

Effects of Amazon deforestation

To parse the drivers, the team combined long-term reanalysis, remote sensing, and land-use classifications (including MapBiomas) with parametric surface equations that track annual cycles and forest loss. Alongside rain and temperature, they examined greenhouse gases. 

Across the past 35 years, CO₂ rose by about 87 ppm and methane by about 167 ppb in the region – increases driven more than 99% by global emissions. That result doesn’t contradict studies showing deforestation weakens the forest’s CO₂ uptake. 

As Machado noted, flux measurements are local, while concentrations reflect the global burden. In other words, global emissions dominate the background rise, even as local clearing erodes the forest’s ability to absorb carbon.

Keep the forest, keep the rain

Project the trends forward and the message is unambiguous. If clearing continues, the experts warn, dry-season rainfall will decline further and temperatures will climb higher, amplifying drought risk and fire weather. 

Other recent work already points to deforestation-driven disruptions of the South American monsoon, which waters central and southeastern Brazil. Weakening that summer lifeline doesn’t just stress farms and cities downstream; it also undercuts the Amazon’s own resilience – making it harder for the forest to recover from shocks like the 2023–2024 droughts.

The new attribution numbers give decision-makers a sharper tool. They quantify how much of today’s dry-season pain is homegrown versus imported via global warming.

That “account payable” puts a premium on preserving standing forest, restoring degraded areas, and reining in fire – actions that can deliver near-term benefits for rainfall and heat, even as the world tackles emissions.

With COP30 convening in Belém, the study’s take-home is as practical as it is urgent: keep the forest intact, and you keep the rain. Every hectare left standing pays climate dividends – locally, season by season, not just in abstract global carbon ledgers.

The study is published in the journal Nature Communications.

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