Where does all the rain in the rainforest come from?
You would think it comes from the Pacific Ocean, since it is so close by. However, in the west of South America, the Andes are up to 6000m high. Rain clouds from the Pacific have no chance of crossing them to reach the Amazon basin. Of course, lots of water also evaporates over the numerous rivers of the continent. Yet that would never be enough to create the up to 2000mm of precipitation that rain down on the area every year. So the rain can only be coming from the Atlantic Ocean. Yet how does it travel up to 5000km from the eastern coast all the way to the furthest corners of Amazonia?
The answer lies in a unique water cycle that the forest itself keeps alive.
The Amazon rainforest has its own invisible river, a continuous stream of fresh water that is invisible to the bare eye. Even though it carries more water than all the rivers of the Amazon basin combined!
It can only exist because the forests of the Amazon basin form the largest coherent rainforest on Earth. And they make their very own weather!
The water that does reach the ground is absorbed quickly by the roots. It rises up to the top of the tree, where it evaporates. One tree „exhales“ around 760 liters of waters per day like this!
So the remaining 74 % of fallen rain will also evaporate soon over the forest and form clouds. The wind pushes them westwards, it rains, and the whole process starts over. This cycle repeats itself about five times until the clouds reach the Andes. That is how the rain can reach even the furthest corners of the Amazon rainforest.
Actually, the plants of the Amazon basin evaporate 20 billion tons of water every day, thereby creating the largest stream of freshwater on Earth!
This system influences our world’s climate in a unique way and emphasizes once again how important it is to protect these forests. The only thing that keeps this water cycle alive is the immense area of coherent rainforest.
That is also why it is so disastrous when forests are cut in the east of Amazonia.
When the clouds from the Atlantic rain down over clear-cut areas, 80% of the water will flow directly back into the rivers. Only 20% can evaporate and be transported further westwards to the interior of the continent. This means that too little water will reach the western parts of Amazonia. The rainforest with its biodiversity will vanish and leave a prairie.
Source: Fabian Mühlberger; „Lebenswelt Regenwald“, Spitzer et al. 2004.