Human-led deforestation is linked to less rain in tropical rainforests, according to a new study published last month in the journal Nature. Large-scale cutting of trees in the Amazon and other rainforests could lead to declining agricultural yields, raise the risk of wildfires and promote irregular precipitation patterns, scientists say.
Robust forests help produce rainfall in a process called moisture recycling. Essentially, trees absorb rainwater and release its moisture back into the atmosphere, contributing to cloud formation and, consequently, more rain.
By disrupting this process, deforestation has a far-reaching impact. The moisture can travel up to an average of 373 miles before falling as precipitation—in regions downwind of the Amazon, for example, up to 70 percent of rain could come from the forest-driven cloud formation, per the paper. This means that when the region is deforested, downwind areas face arid, harsher climates.
“When we’re removing trees, we’re making the environment drier and that lack of moisture that’s the big cloud above those trees just disappears,” lead author Callum Smith, a deforestation researcher at the University of Leeds in England, tells NPR’s Lauren Sommer and Seyma Bayram.
The researchers examined precipitation and deforestation patterns in the Amazon rainforest, Congo Basin and Southeast Asia, which hosts the Leuser Ecosystem, a forested area of Indonesia. Using satellite data from 2003 to 2017, they identified significant drops in average rainfall in each of these regions. The impacts were visible even at small scales, but the most dramatic changes could be seen over wide areas: At the scale of about 15,500 square miles, scientists found that rainfall decreased 0.25 millimeters per month for every percentage point of forest loss.
Importantly, the researchers demonstrate a correlation between rising human activity and decreases in local rainfall.
“This study reinforces the understanding that deforestation reduces rainfall, which reduces forest resilience and increases the risk of tipping points and negative impacts on local economic activities,” Bernardo Flores, an ecosystem resilience researcher at the Federal University of Santa Catarina in Brazil who was not involved with the study, tells Mongabay’s Sarah Brown.
Experts warn the Amazon is approaching a “tipping point” that will result in drier conditions, turning its leafy vegetation into a savanna. This would threaten the wildlife in the Amazon rainforest, which is one of the most biodiverse places on Earth, home to one in ten of the planet’s known species. The rainforest has been nicknamed the “lungs of the planet” for the way it sucks up vast amounts of carbon dioxide each year.
But some dangerous changes are already occurring—the dry season in the Southern Amazon is now four to five weeks longer than it was in 1970, says Carlos Nobre, an earth system scientist who contributed to first identifying the Amazon’s tipping point, to Mongabay.
“Once we deforest, we lose one of our greatest natural defenses in protecting ourselves from climate change. This is not only true for forests, but also other ecosystems,” says Robin Averbeck, forest program director at the Rainforest Action Network, to NPR.
However, efforts to stop deforestation are complex. In the Congo Basin, for example, much of the forest loss is due to poor, small-scale farmers trying to survive. Frances Seymour, senior fellow at the nonprofit World Resources Institute, tells NPR it’s important to distinguish corporations and governments engaging in deforestation practices from local communities who are trying to make a living.
The impact on rainfall shown in this study could be an effective argument against deforestation for governments and companies cutting down rainforests, co-author Dominick Spracklen, an expert on biosphere-atmosphere interactions at the University of Leeds, tells the Guardian’s Jonathan Watts. The idea that forests should be conserved to store carbon has greater sway in the northern hemisphere, while the immediate effects on hydrology are more personal to those who live near the trees.
“Demonstrating the local benefit of keeping tropical forests standing for the people living nearby has important policy implications,” Spracklen tells the Guardian.
Brazil has worked to reduce the amount of deforestation in the Amazon since the early 2000s, wrote Jason Daley for Smithsonian magazine in 2019. Luiz Inácio Lula da Silva led efforts to decrease deforestation when he served as president of Brazil from 2003 to 2010, but former president Jair Bolsonaro oversaw an increase in deforestation after he took office in 2019. On January 1, 2023, Lula was sworn into the presidency again, after running a campaign that focused on environmental preservation and increased protections for Indigenous communities. Indigenous lands contain around 80 percent of Earth’s biodiversity.
“The Amazon is important for everyone in the world,” says Flores to NPR. “When humanity faces problems in the future that we now don’t even imagine now, the solutions can come from the Amazon.”