Rainforests, Cloud Fountains, and the Flying River of Brazil

Which came first, the rainforest or the
rain? Well we all know that water is needed by trees to grow, so you have to
start with rain. But what I want to explain is how tropical rainforest trees
recycle the rain back into the atmosphere to create the flying river of
Brazil. So, in this image here, you can see wind vectors represented as white lines,
and we want to see where the rain starts for the Amazon region of Brazil. If you
look at northern South America, you can see that the wind pushes moist air off
of the Atlantic Ocean, over the Amazon, where it forms clouds and then falls as
rain to support tree growth. Now, the trees themselves take up this water. It’s
sucked up through the roots, it travels up through the stems and out through
tiny pores in the leaves called stomata, back into the atmosphere. But where do we
get the energy to move water against the force of gravity up to the top of a tall
tree? Well, this relies on a fundamental idea in plant biology called the
“cohesion tension theory.” Water molecules are cohesive, they stick together through
a process called hydrogen bonding, and that creates these chains of water
molecules that can be pulled through tiny cellular passages called xylem just
by the force of evaporation up into the atmosphere. And there they condense, and
form clouds. So when I see a tree I don’t just see leaves and branches, I see a
cloud fountain that is spouting water into the air. In the Amazon region, the
trees, all together, put about 20 billion tons of water back into the air each
year and this falls as rain. And you can see the abundant clouds forming there
over the Amazon region in this model simulation. However, this rain does not
just fall on the rain forest. The wind off the Atlantic moves across
South America, it hits the Andes Mountains, and then it travels south, carrying the clouds and the water with it. And it brings rain to fields of
soybean, sugarcane, coffee, all kinds of agriculture in southern Brazil and
southern South America. The amount of water that’s carried by these wind
currents is actually thought to be as great as the discharge of the Amazon
River itself into the Atlantic Ocean each year. And that’s why we call this,
“the flying river”. Now, what if we have rain forest destruction? You can see this
happening in this series of images that were taken over Rondônia, Brazil over a
ten-year period, which is in the southern Amazon region. And what scientists worry
about is if we don’t have trees, the water that’s coming off the Atlantic
Ocean and falling onto the Amazon region will not return to the atmosphere. It
will simply run off into the rivers. And that means the flying river will dry up.
And that means for southern Brazil and southern South America, drought and loss
of crop productivity. So, the key is, when you save the rainforest, you actually
save the rain itself. Thank you.

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