They act as giant sponges for the large amounts of rain which fall on them, soaking up the moisture and gradually releasing it into rivers and lakes. This process is called 'watershed' and enables a constant supply of clean water to reach rivers and lakes for irrigation. They are also instrumental in keeping other areas moist. Tropical rainfall helps regulate global rainfall patterns. Land which is hundreds or thousands of miles away from the rainforests is affected by them.
Rainforests also play an essential part in regulating the earth's atmosphere.
The gases in the atmosphere control the amount of sunlight that reaches the earth. These must be kept in balance for living things to survive. If there is either too much or too little sun, all living things will die. Trees act as the earth's lungs, managing the amounts of carbon dioxide and oxygen in the global atmosphere. Too much carbon dioxide in the atmosphere is poisonous for living creatures.