The Americas Explained: How Trees in the Amazon Can Control the Weather
Trees in the Amazon release water into the air, then call it back when they're thirsty.
In every episode of The Americas’ epic 10-part adventure through the natural world, we visit another part of Earth’s great supercontinent and spend some time with the plants and animals who call it home. In tonight's incredible fourth episode, "The Amazon," we traveled to the Amazon rainforest, a hotbed of biological diversity and one of the most iconic, not to mention most beautiful, landscapes on the planet.
The Amazon is the largest and most diverse rainforest on Earth, home to 400-pound giant snakes, capybaras (the world’s largest and perhaps chillest rodent), and the world’s biggest river. It’s a place where, as host Tom Hanks tells us, the trees themselves can make it rain.
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The Americas Episode 4 shows how trees, plants, and fungi in the Amazon can control the weather
The Amazon rainforest stretches across nine countries, covering 40% of the South American continent. At the heart of the forest is the Amazon River, the largest river in the world with more than 1,100 tributaries. It contains 15% of all the fresh water on Earth, and it’s that water which sustains the rainforest’s dense biosphere.
As trees live and grow, they pull moisture up through their trunks and to their leaves. Then, the leaves respirate and exhale that water vapor into the surrounding air. With approximately 400 billion trees in the Amazon, there’s roughly 20 billion tons of water released into the atmosphere every day. Getting the water vapor back to the ground in the form of rain takes another trick.
While the Amazon is never really dry, it does go through a rainy season and a dry season, when rainfall is lighter. Scientists realized that the rainy season arrives in the Amazon two or three months earlier than expected, based on seasonal wind patterns in the area. Research revealed that during the dry season, when photosynthesis is at its strongest, trees release more water vapor than at other times. All that water vapor has the potential to form big rain clouds, but there needs to be tiny particles in the air for droplets to form around. The trees take care of that too.
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When scientists gathered air samples from above the treetops, they found tiny particles from tree resin, organic compounds released by tree leaves, and potassium salts from plants and fungal spores. Those particles provide the seeds around which water droplets can grow, triggering a storm. Through the complex interactions of plants and fungi, the rainforest releases water into the air and calls it back when needed.
When the rainy season arrives, there’s so much water that it completely reshapes the environment. The Amazon River swells and breaks its banks. Rushing water floods into the forest until only the very tops of the trees are peaking through the water’s surface.
The water gets as deep as 40 feet and covers an area larger than the state of Montana, bringing nutrients inland. Animals which usually dwell on the forest floor take to the treetops in search of safety. Meanwhile, aquatic animals make inland incursions. Schools of piranha arrive to feast on a forest buffet usually beyond their reach, and pink river dolphins use echolocation to hunt among the trunks and branches of trees.
Eventually the waters recede, taking the underwater visitors with it. The piranha and the dolphins won’t return until the next year, when the forest calls for rain again.
Where can you watch The Americas?
Future episodes of The Americas will air weekly on Sundays at 8:00 pm ET on NBC, and stream on Peacock the following day!
