“The water cycle, 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. The water moves from one reservoir to another, such as from river to ocean, or from the ocean to the atmosphere, by the physical processes of evaporation, condensation, precipitation, infiltration, runoff, and subsurface flow. In doing so, the water goes through different phases: liquid, solid, and gas.”
http://en.wikipedia.org/wiki/Water_cycle
The global water cycle can be described with nine major physical processes which form a continuum of water movement.
1) Evaporation – occurs when the physical state of water is changed from a liquid state to a gaseous state.
2) Condensation – is the process by which water vapor changes it’s physical state from a vapor, most commonly, to a liquid.
3) Precipitation – is the process that occurs when any and all forms of water particles fall from the atmosphere and reach the ground.
4) Interception – Is the process of interrupting the movement of water in the chain of transportation events leading to streams. The interception can take place by vegetal cover or depression storage in puddles and in land formations such and rills and furrows.
5) Percolation – is the movement of water though the soil, and it’s layers, by gravity and capillary forces.
6) Infiltration – is the physical process involving movement of water through the boundary area where the atmosphere interfaces with the soil.
7) Transpiration – Water inside of plants is transferred from the plant to the atmosphere as water vapor through numerous individual leave openings.
8) Runoff – is flow from a drainage basin or watershed that appears in surface streams.
9) Storage -There are three basic locations of water storage that occur in the planetary water cycle. Water is stored in the atmosphere; water is stored on the surface of the earth, and water stored in the ground.
http://www.nwrfc.noaa.gov/info/water_cycle/hydrology.cgi
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