Why the Amazon’s ability to make its own rain matters more than ever

Dr. Magali Nehemy stood on the banks of the Tapajós River in the Amazon rainforest when the community’s chief—a man in his seventies who had lived there his whole life—looked out over the bare shoreline and shook his head. 

“I’ve never seen it this dry,” he told her. 

The water was far lower than it should have been for that time of year. The riverbank, normally submerged, sat bare in the heat.  

For Dr. Nehemy, an ecohydrologist based at UBC Okanagan, the moment captured the paradox of the Amazon: a system vast enough to influence the planet’s climate, yet fragile enough that a single dry season can disrupt what long-time residents see as normal. 

The Amazon is often called the “lungs of the planet.” It is a familiar phrase, and a misleading one, Dr. Nehemy says. 

“There's a researcher, Luciana Gatti, who calls the Amazon the ‘airbag’ of the world,” Dr. Nehemy says. “It absorbs shock. The water stored in the soil, the carbon stored in the forest—it buffers change.” 

Dr. Nehemy was born and raised in Brazil, studying at the University of São Paulo before moving to Canada for her master’s and PhD. She now returns to the Amazon as a researcher, studying how forests and water interact—and how that relationship is changing. 

Her work reveals that the system is both more self-sustaining and more vulnerable than previously believed. 

During the dry season, Amazonian trees continue to pull water from the soil and release it into the atmosphere through their leaves. This process, known as transpiration, helps generate new rainfall above the canopy. 

In a recent study published in the Proceedings of the National Academy of Sciences, Dr. Nehemy and her collaborators found that during the dry season, most of the water used by trees in eastern Amazon forests does not come from deep underground reserves.  

Instead, it comes from the top 50 centimetres of soil—rain that fell only weeks or months earlier. 

“I would like us to be able to predict how water is changing across landscapes,” she says, “and to understand which regions are most vulnerable.”  

This discovery challenged a long-held assumption that trees must rely primarily on deep groundwater during dry periods. Instead, the forest relies on recent rain—a much more fragile and unpredictable source. 

The difference, it turns out, is partly biological. 

Some tree species are better equipped to withstand dry conditions than others. Dr. Nehemy’s work links embolism resistance—a tree’s ability to keep water moving through its tissues under stress—to the forest’s ability to continue recycling water into the atmosphere. 

Species that resist hydraulic failure can keep transpiring even as soil moisture drops. That ability helps stabilize local climate and sustain rainfall. In this way, biodiversity itself becomes a form of climate resilience. 

The Tapajós region, where Dr. Nehemy conducts her research, is not just a field site. People live there. They depend on the forest and its rivers in tangible, daily ways. 

Many communities are semi-isolated, using waterways as roads. When rivers shrink, transportation stops. Food access shifts. So does access to medicine, supplies and safety. 

“Most of the land that is protected in the Amazon is within Indigenous territories,” she says. “And yet Indigenous communities are often not included in the decisions that shape research and policy.” 

In that sense, climate change is not only an environmental issue. It is also a governance issue, a cultural issue and a question of equity. 

Dr. Nehemy is deliberate in how she speaks about the Amazon. She does not claim to be its voice. She does not overstep her data. She stays anchored in what can be observed and measured. 

What she does know is that rising temperatures are increasing the amount of water being pulled into the atmosphere, while reducing the amount that remains in rivers, lakes and soils. 

This isn’t just the Amazon’s concern. 

From the rainforests of South America to dry valleys in British Columbia, the mechanics are connected. Change vegetation. Change temperature. Change everything. 

“The Amazon produces its own rain by quickly returning water to the atmosphere and producing its own rainfall when it needs it most, during the dry season,” she says. “Transpiration is the largest water flux on land. When we change forests, we change that flux. And when we change that, we change the water available to everything else.”