Water cycle

Water Cycle

The Water Cycle (pronunciation: /ˈwɔːtər ˈsaɪkəl/), also known as the Hydrologic Cycle or the H2O Cycle, describes the continuous movement of water on, above, and below the surface of the Earth. The mass of water on Earth remains fairly constant over time but the partitioning of the water into the major reservoirs of ice, fresh water, saline water and atmospheric water is variable depending on a wide range of climatic variables.

Etymology

The term "Water Cycle" is derived from the two English words "water" and "cycle". "Water" comes from the Old English "wæter", of Germanic origin; related to Dutch "water" and German "Wasser". "Cycle" comes from the Greek "kyklos", meaning circle or wheel, which is related to the word "kuklos" meaning wheel or circle.

Process

The water cycle involves several key stages:

• Evaporation is the process by which water changes from a liquid to a gas or vapor. This is the primary pathway that water moves from the liquid state back into the water cycle as atmospheric water vapor.

• Transpiration is the process by which moisture is carried through plants from roots to small pores on the underside of leaves, where it changes to vapor and is released to the atmosphere.

• Condensation is the process by which water vapor in the air is changed into liquid water. Condensation is crucial to the water cycle because it is responsible for the formation of clouds.

• Precipitation is water released from clouds in the form of rain, freezing rain, sleet, snow, or hail. It is the primary connection in the water cycle that provides for the delivery of atmospheric water to the Earth.

• Runoff is the variety of ways by which water moves across the land. This includes both surface runoff and channel runoff. As it flows, the water may infiltrate into the ground, evaporate into the air, become stored in lakes or reservoirs, or be extracted for agricultural or other human uses.

• Infiltration is the process by which water on the ground surface enters the soil. Infiltration is governed by two forces, gravity and capillary action.

Related Terms

• Hydrosphere
• Atmosphere
• Biosphere
• Cryosphere
• Groundwater
• Water Vapor
• Evapotranspiration

External links

• Medical encyclopedia article on Water cycle
• Wikipedia's article - Water cycle

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