The flow of water in a tropical forest is actually made up of several small cycles. Water always enters the system as precipitation (rain or snow). Then several things may happen. Some water falls on trees or the ground and is directly evaporated back into water vapor. Other water hits the ground and runs off to join streams and rivers on their way to the ocean where it will eventually evaporate. Still more water is absorbed directly by the roots of trees and does not reenter the cycle until it is transpired (released) as water vapor by the leaves of the tree. Finally, some water will seep into the ground to become ground water, or part of the water table.
The tropical forest has certain characteristics that strongly affect the flow of water. The thick canopy layer in most tropical areas tends to catch a majority of the rain that falls there. It then is either directly absorbed by the plants or evaporates back into the clouds. This is a very important aspect of the tropics as tropical soil is so thin that it would be washed away without the canopy's protection (see the tropical soils section). Any rain that does not reach the ground is quickly absorbed by the above-ground air or prop roots of the tropical trees. Very little water escapes to become runoff or ground water.
