Forest Destruction Along Southern Edge Of Amazon Basin Making The Region's Dry Season Substantially Drier -- And Quickly

In Brazil’s southern Amazonian region, where the notorious “arc of deforestation” has been expanding since the 1970s, forest loss is reshaping the region’s atmospheric water cycle. As the Amazon Rainforest releases moisture into the atmosphere, it fuels the rains that feed rivers, crops, wildlife and communities. But as deforestation disrupts the water exchange between forest and atmosphere, it significantly reduces the amount of rain in the dry season, researchers have recently found.

The team from Nanjing University, China, and the University of Leeds, U.K., analyzed how deforestation in the states of Rondônia and Mato Grosso — which together are responsible for about 30% of all deforestation in the Brazilian Amazon in recent decades — affected the atmospheric water cycle between 2002 and 2015. They found that a 3.2% mean loss of forest cover led to a 5.4% reduction in dry season rainfall, highlighting that precipitation in the Amazon is highly sensitive to changes in forest cover. Deforestation deals a “double whammy” of blows to the climate, Dominick Spracklen, study co-author and professor of biosphere-atmosphere interactions at the University of Leeds, told Mongabay by phone. In addition to reducing how much water vapor is pumped into the atmosphere via evapotranspiration, deforestation also weakens the atmosphere’s ability to pull in water vapor from other regions.

By altering how Earth’s surface absorbs and reflects heat, deforestation led to warmer, drier air above the study area. This dry air impaired atmospheric convection, a process that moves warm air up and brings cool air down and plays a crucial role in transporting heat and moisture through the atmosphere. Weaker convection pulled even less moisture from other regions into the study area, further increasing atmospheric dryness. The reduction in atmospheric moisture from other regions was responsible for 76% of the observed drop in dry-season rain, the authors found.

Warmer, drier air also slashes the amount of water vapor that can be recycled as rain, lowering precipitation efficiency — the ratio between the moisture in the air that could turn into rain and the amount of rain that actually falls. Alongside convection, reduced precipitation efficiency is one of the main drivers behind reduced rainfall in the dry season. Such a decline can have wide-ranging impacts, including a rise in forest fires, poor agricultural yields, and water shortages. The latter can bring rivers to unnavigable levels, making life difficult for local communities. According to Spracklen, people in remote villages complain they can’t access the waterways they use every day. “There are communities where temperatures have gone way above what we’ve seen in living memory, and the cause is a combination of global climate change and deforestation.”

EDIT

https://news.mongabay.com/2025/09/more-deforestation-leads-to-a-drier-dry-season-amazon-study-finds/