Reference Work Entry


Part of the series Encyclopedia of Earth Science pp 330-331

Hydrologic cycle

  • Ray Kenny
The hydrologic cycle describes the complex and dynamic distribution, transfer and temporary storage of water over and under the Earth's surface. As the term cycle suggests, there is a recurring succession of events (evaporation, condensation, precipitation, surface runoff, subsurface infiltration, and evapotranspiration) that keep nearly all near-surface water in an endless circulation pattern (Figure H5).
Figure H5

The hydrologic cycle. Numbers indicate the amount of water transferred annually (× 103 km3).

All of Earth's surface and near-surface water has accumulated through a gradual release of water from volcanic activity (juvenilewater). The primary reservoir of water is the ocean, which contains greater than 97% of all surface water on Earth. Solar energy evaporates water from the ocean; approximately 13 million metric tons of water per year per average square kilometer are converted to atmospheric vapor. The amount of water evaporated varies conside ...

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