A new study has found that extensive forest loss in Brazil’s southern Amazon is directly causing a significant reduction in dry season rainfall. Researchers from Nanjing University and the University of Leeds found that between 2002 and 2015, a 3.2% loss of forest cover in the states of Rondônia and Mato Grosso led to a 5.4% drop in dry season rain, a phenomenon that is already fueling wildfires, stressing crops, and affecting communities.
A “Double Whammy” on the Water Cycle
The study, published in AGU Advances, explains that deforestation deals a “double whammy” to the climate. First, it reduces evapotranspiration, the process by which trees release water vapor into the atmosphere. Second, it alters how the Earth’s surface absorbs heat, leading to warmer, drier air that impairs atmospheric convection. This weaker convection in turn reduces the atmosphere’s ability to pull in moisture from other regions, accounting for 76% of the drop in rainfall.
According to co-author Dominick Spracklen, a professor at the University of Leeds, these consequences are already here. Brazil faced one of its worst droughts in decades in 2023 and 2024, with unprecedented wildfires affecting millions of hectares of primary forest. Communities are struggling with water shortages and unnavigable rivers.
Undermining Agriculture and a Call to Action
The study warns that this trend of reduced rainfall, driven largely by clearing land for agriculture, is a self-defeating strategy. Continued deforestation could cost Brazil hundreds of billions of dollars in agricultural losses by 2050.
Scientists say the solution requires a two-pronged approach: a global shift away from fossil fuels and, most importantly, an immediate stop to deforestation. They emphasize that primary forests are critical for providing the moisture that sustains agriculture and local communities, and once they are gone, their ecological functions are difficult to restore.