The relative humidity remains high throughout the year. Climate and vegetation growth are mutually dependent. It is this combination of moisture and warmth which aids rapid plant growth, hence the density of rainforest vegetation. Tropical rainforests form a green belt around the earth. They perform several vital environmental functions which control both local and global climates.
Rainforests are essential in keeping their locale moist.
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.