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Sunlight pours around a "flying river"—a vast, humid air current—in an undated picture of the Amazon rain forest.

Sunlight pours around a "flying river"—a vast, humid air current—in an undated picture of the Amazon rain forest.

Photograph courtesy Gérard Moss, Flying Rivers Project

Christine Dell'Amore

National Geographic News

Published December 18, 2009

The Amazon's "flying rivers"—humid air currents that deliver water to the vast rain forest—may be ebbing, which could have dire consequences for the region's ability to help curb global warming, an expert said this week at the Copenhagen climate conference.

Rising temperatures in the Amazon region, in large part due to climate change, are creating more arid savannas, which disrupt the water cycle vital to Brazil's farming and energy industries.

Deforestation also plays a role. As more of Brazil's rain forests fall to logging and agriculture, there are fewer trees to release the water vapor that creates these flying rivers.

Until recently, Amazon forest loss has been primarily linked to the trees' role in trapping greenhouse gases, such as carbon dioxide (CO2), which are a root cause of global warming.

"Most people look at the Amazon as the lungs of the world, or as a solution to capture CO2," said Gérard Moss, an engineer and founder of the Flying Rivers Project, an ongoing effort to document the humid air currents and their effects.

"But I'd like people to realize that the Amazon Basin is a huge water pump—rain is [our] most valuable asset," he said by phone Wednesday in Copenhagen, where he gave a press briefing on the project earlier this week.

Flying rivers may transport as much water as the Amazon River itself, he added. "This huge rain machine needs to be preserved."

Watery World

The Amazon region is awash with fresh water: 3,700 cubic miles (15,400 cubic kilometers) falls from the sky each year, the highest rate of rainfall in the world. The runner-up is Russia, with a yearly rate of 1,900 cubic miles (7,800 cubic kilometers).

Flying Rivers Project scientists—led by agronomist and Amazon-rainfall expert Enéas Salati—have determined that a single large tree in the center of the Amazon forest can give off up to 317 quarts (300 liters) of water in a day. (See rain forest pictures.)

In a process called evapotranspiration, trees draw water from their roots and then "transpire" some of that water back into the air.

Since 2003, Moss has flown through Brazil's airborne rivers in a single-engine plane to collect water vapor samples. The vapor's chemical "footprints" are then analyzed at the Center for Nuclear Energy in Agriculture (CENA) in Piracicaba, in the state of Sao Paulo.

The project's goal has been to figure out where the water comes from and then map how wind currents carry water across the vast Amazon Basin. For instance, Salati's research in the 1980s showed that more than half of the Amazon's rainfall emanates from trees, with the rest coming from vapor from surface water bodies.

Moss recently completed a seven-day research trip along the trajectory of one flying river that ends in the city of Sao Paulo. Those results showed that the wet air current flowed at 1,990 miles (3,200 kilometers) a second—about as fast as a major river.

The Brazilian rain forest's moisture is important for sustaining South American rainfall, especially the winter monsoons, noted Helene Muri, of the Institute of Astronomy and Geophysics at the Catholic University of Louvain in Belgium.

"So if the trees are chopped down, the rainfall rates could be reduced through this mechanism," Muri said by email.

Any changes in vegetation can impact the local "water budget" and create drought conditions that impact agriculture and industry, she added.

Withering Economy

Brazil's economy may wither if the flying rivers dry out, project founder Moss said.

Farmers in the Amazon's fertile Matto Grosso state are highly dependent on Amazon rain to grow their crops, for example. The agriculture industry in the region is extremely profitable because so little irrigation is needed.

"Rainwater has been taken for granted ... ," Moss said.

"In addition, 80 percent of Brazil's energy is related to hydroelectric power, so every single drop of rain counts," Moss said. "If we start losing rain, it will have a huge impact [on our energy]."

But Moss added that the need to preserve rain forests has percolated into the public consciousness in Brazil.

"More people are realizing," he said, "that the well-being of many people in the southern parts [of Brazil] is related to every tree in the Amazon."

The Flying Rivers Project is funded by the National Water Regulatory Agency (ANA) and by Petrobras, an oil company in Brazil.

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