For decades, the dry season in the Amazon rainforest has been getting drier. A new study, published on Tuesday, found that about 75 percent of the decrease in rainfall is directly linked to deforestation.

The study, in Nature Communications, also found that tree loss was partly responsible for increased heat across the Amazon. Since 1985, the hottest days in the Amazon have warmed by about 2 degrees Celsius. About 16 percent of that increase, the researchers found, was because of deforestation.

Marco Franco, an assistant professor at the University of São Paulo who led the study, said he was surprised by the findings. “We were expecting to see deforestation as a driver, but not this much,” he said. “It tells us a lot about what’s going on in the biome.”

The Amazon rainforest is often called the lungs of the planet because its trees help to regulate the global climate by absorbing planet-warming carbon dioxide. But decades of large-scale logging and burning in the forest have recently flipped that script, and parts of the region have become net producers of greenhouse gases.

The Amazon also steers regional weather patterns. Its trees pull water from the soil and, through a process known as transpiration, release that moisture through tiny pores on their leaves. There are hundreds of billions of trees in the Amazon Basin, and the water they collectively release into the air is estimated to contribute more than 40 percent of all the region’s rainfall.

“You can imagine a tree as a big water pump,” said Callum Smith, a postdoctoral researcher at the University of Leeds in England who studies tropical deforestation and was not involved in the Nature Communications study. “If you chop down a tree, it reduces the moisture going into the atmosphere.”