A forest does more than receive rain. Through billions of trees working together, it can help create the conditions for rain to fall.
Trees draw water from the soil through their roots. The water travels up the trunk and reaches the leaves, where tiny pores called stomata release it into the air as vapor. This process is known as transpiration. A single tree makes only a small contribution, but an entire forest sends enormous amounts of moisture into the atmosphere every day.
As the vapor rises, it can cool and condense into clouds. Some of that water then returns to the ground as rain, where trees absorb it again. In tropical rainforests, this cycle is remarkably efficient. Around 40% of the Amazon's rainfall is thought to come from water released by the forest itself. Scientists estimate that a raindrop may fall, evaporate and return as rain five or six times while moving across the Amazon Basin.
The moisture does not necessarily fall where it first entered the air. Winds can carry it hundreds or even thousands of miles, creating vast currents sometimes called "flying rivers." These currents can transport more water than some of the world's largest rivers.
Moisture from the Amazon helps bring rain to large parts of South America. Similar systems operate in the Congo Basin and Southeast Asia. Studies have found that air passing over thick tropical forest can produce about twice as much rain as air moving over land with little vegetation.
Some researchers have proposed a wider explanation called the "biotic pump" hypothesis. It suggests that forests do more than recycle water. By affecting atmospheric pressure, they may also help pull moist ocean air farther inland. This could help explain why rainfall can remain heavy even deep inside large forest regions. However, the idea is still described as a hypothesis rather than a settled explanation.
The cycle can weaken when forests are cleared. With fewer trees, less water returns to the atmosphere, so fewer clouds may form and less rain may fall. Longer dry seasons can leave the remaining forest more vulnerable to fire. That damage may then reduce rainfall further.
A forest, in other words, is not simply watered by the weather. It is one of the forces helping to make that weather.