The Hydrologic Cycle

The Hydrologic Cycle--Illustrated

Water falls to the earth as rain, snow, or less frequently, hail.

When the water reaches the earth's surface, it may:

Soak directly into the ground

Run back into a stream, a lake, or the ocean immediately

Evaporate and return to the atmosphere

Be taken up by the roots of trees, grass, and other plants

Remain frozen and become part of a glacier or polar caps

Water that soaks into the ground may be stored as groundwater, or it may slowly move out toward a stream. The groundwater may be stored for many years or it may be pumped from a well for household, agricultural, or industrial uses. The groundwater that reaches streams provides much of the water found in the stream when it is not raining or snow is not melting.

Groundwater accounts for 0.612 percent of the earth's water.

Water contained in lakes, streams and oceans may evaporate and become rain or snow. This water is also used by people and animals.

Rivers contain 0.001 percent of the earth's water.

Fresh water lakes contain 0.009 percent of the earth's water.

Oceans contain 97.137 percent of the earth's water.

Water is evaporated from bodies of water, the soil, and from vegetation. Plants take up water through their roots and release water vapor through their leaves. This water vapor forms clouds which can in turn produce precipitation.

The atmosphere contains 0.001 percent of the earth's water.

Polar ice caps and snow account for 78 percent of the world's fresh water supply.

Ice caps and snow contain 2.240 percent of the earth's water.

Source:

Hewlett, J.D. Principles of Forest Hydrology. Athens, Georgia: University of Georgia Press, 1982.

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