Deforestation is largely to blame, according to a new study.

The study, published in Nature Communications, found that roughly 75 percent of the drop in rainfall can be directly linked to deforestation, Sachi Kitajima Mulkey reported for The New York Times.

“We were expecting to see deforestation as a driver, but not this much,” Marco Franco, an assistant professor at the University of São Paulo who led the study told The New York Times. “It tells us a lot about what’s going on in the biome.”

In the Amazon, more than 40 percent of the region’s rainfall comes from trees, which release water vapor into the air through a process known as evapotranspiration.

It’s simple math: fewer trees means less moisture in the air.

Scientists have long known about the connection between deforestation and declining precipitation, but it’s a difficult effect to study and quantify as weather changes can appear far from areas where the deforestation actually occurred.

Indeed, the study also connects deforestation to higher temperatures in the Amazon, generally, finding the hottest days increased by roughly 2 degrees Celsius, in part due to deforestation.

To understand the impact, the researchers pored over 35 years of annual data from key sections of the Brazilian Amazon, using satellite data and advanced analytical methods to measure changing climate and weather patterns, while sifting out other influences like evolving landscapes.

Luiz Machado, a professor of climate and meteorology at the University of São Paulo and an author of the study, told The New York Times that while it’s common knowledge that climate change and deforestation have altered the Amazon, until this study, “nobody knew exactly what each of these things contributed.”

The authors also note that a 75 percent drop in precipitation is an average across the Amazon Basin — areas with higher levels of deforestation experienced even greater rainfall declines.

This is because years of deforestation have pushed the rainforest into a vicious cycle: As large areas are cleared of trees, the forest loses its ability to retain moisture and recycle that water back into the atmosphere. This contributes to longer periods of drought, which in turn, spur intense fire seasons that destroy even more trees.

If this cycle of destruction continues, the rainforest could be pushed to an ecological tipping point, transforming permanently into a dry savanna.

The continued deforestation of the Amazon would be disastrous for the Earth’s climate. Conservation International studies have shown that the Amazon rainforest stores more irrecoverable carbon — carbon that, if emitted into the atmosphere, could not be restored in time to prevent the worst impacts of climate change — than any other region on Earth.

While new protected areas are popping up around the world as countries work to meet global climate goals like 30 by 30, deforestation continues to run rampant. In 2024, more than 40 million acres of the Amazon rainforest burned, and the first six months of 2025 saw deforestation reach 27 percent higher than the first half of 2024.

As climate change makes forests both more vital and more vulnerable, protected areas remain one of our best tools to keep forests standing. Conservation International recently supported the creation of three new protected areas in the Amazon, protecting huge swaths of threatened forest and keeping vast amounts of carbon out of the atmosphere.

Further reading:

• What drives deforestation — and how can we stop it?
• Study: Protected forests are a climate powerhouse

Mary Kate McCoy is a staff writer at Conservation International. Want to read more stories like this? Sign up for email updates. Also, please consider supporting our critical work.