The water cycle—technically known as the hydrologic cycle—is the circulation of water within the earth's hydrosphere, involving changes in the physical state of water between liquid, solid, and gas phases. The hydrologic cycle refers to the continuous exchange of water between atmosphere, land, surface and subsurface waters, and organisms. In addition to storage in various compartments (the ocean is one such "compartment"), the multiple cycles that make up the earth's water cycle involve five main physical actions: evaporation, precipitation, infiltration, runoff, and subsurface flow: Download high resolution version (860x589, 761 KB)Water cycle http://ga. ... Hydrosphere (Greek hydro- means water) in physical geography, describes the collective mass of water found on, under, and over the surface of a planet. ... Water (from the Old English word wæter; c. ... Earths atmosphere is the layer of gases surrounding the planet Earth and retained by the Earths gravity. ... Land is sometimes used synonymously with country. ... Surface water is water on the ground or in a stream, river, lake, sea or ocean; as opposed to groundwater. ... In biology and ecology, an organism (in Greek organon = instrument) is an assembly of organs that influence each other in such a way that they function as a more or less stable whole and have properties of life. ... Evaporation is the process whereby atoms or molecules in a liquid state (or solid state if the substance sublimes) gain sufficient energy to enter the gaseous state. ... Run-off, composed of a mixture of water and soil along with any other organic or inorganic substances that may exist in the land, is the product of precipitation, snowmelt, over-irrigation, or other water coming in contact with the earth and carrying matter to streams, rivers, lakes, and other...

• Evaporation is the transfer of water from bodies of surface water into the atmosphere. This transfer entails a change in the physical nature of water from liquid to gaseous phases. Along with evaporation can be counted transpiration from plants. Thus, this transfer is sometimes referred to as evapotranspiration. 90% of atmospheric water comes from evaporation, while the remaining 10% is from transpiration.
• Precipitation is atmospheric moisture that has previously condensed to form clouds (changed from the gas phases to a liquid or solid phase), falling to the surface of the earth. This mostly occurs as rainfall, but snow, hail, fog drip, and other forms participate as well.
• Interception is precipitation trapped by vegetation instead of falling directly onto the soil.
• Infiltration into the ground is the transition from surface water to groundwater. The infiltration rate will depend upon soil or rock permeability as well as other factors. Infiltrated water may reach another compartment known as groundwater (i.e., an aquifer). Groundwaters tend to move slowly, so the water may return as surface water after storage within an aquifer for a period of time that can amount to thousands of years in some cases. Water returns to the land surface at lower elevation than where it infiltrated, under the force of gravity or gravity induced pressures.
• Runoff includes the variety of ways by which land surface water moves down slope to the oceans. Water flowing in streams and rivers may be delayed for a time in lakes. Not all precipitated water returns to the sea as runoff; much of it evaporates before reaching the ocean or reaching an aquifer.
• Subsurface flow incorporates movement of water within the earth, either within the vadose zone or aquifers. After infiltrating, subsurface water may return to the surface or eventually seep into the ocean.

Transpiration is a continuous process caused by the evaporation of water from leaves of plants and its corresponding uptake from roots in the soil. ... Evapotranspiration (ET) is the sum of evaporation and plant transpiration. ... Water vapor condensing over a cup of hot tea Water vapor or water vapour, also aqueous vapour, is the gas phase of water. ... Cumulus of fair weather A cloud is a visible mass of condensation droplets or ice crystals suspended in the atmosphere above the surface of the Earth or another planetary body. ... Rain falling For other uses see Rain (disambiguation). ... A fresh snowfall in Colorados (USA) high forests. ... A large hailstone Hail is a type of graupel (a form of precipitation) composed of spears or irregular lumps of ice. ... Early morning fog obscures the surface of this lake in Carrollton, Georgia, but the sky remains clear. ... Groundwater is water flowing within aquifers below the water table. ... In geology, permeability is a measure of the ability of a material (typically, a rock) to transmit fluids through it. ... An aquifer is an underground layer of water-bearing permeable rock, or permeable mixtures of unconsolidated materials (gravel, sand, silt, or clay) (see also groundwater). ... It has been suggested that Law of universal gravitation be merged into this article or section. ... Ocean (from Okeanos, a Greek god of sea and water; Greek ωκεανός) covers almost three quarters (71%) of the surface of the Earth, and nearly half of the worlds marine waters are over 3000 m deep. ... Running Stream The primary meaning of stream is a body of water, confined within a bed and banks and having a detectable current. ... The Murray River in Australia. ... A lake is a body of water surrounded by land. ... The vadose zone, also termed the unsaturated zone, is the portion of Earth between the land surface and the water table, and is thus not considered groundwater (vadose is Latin for shallow). It comprises the unsaturated portion of the soil, regolith or bedrock, as well as the saturated capillary fringe... An aquifer is an underground layer of water-bearing permeable rock, or permeable mixtures of unconsolidated materials (gravel, sand, silt, or clay) (see also groundwater). ...

See also

• ecohydrology
• hydrology
• water resources
• biogeochemical cycle

Ecohydrology is a sub-discipline of hydrology that focusses on ecological processes involved in the hydrological cycle. ... Water covers 70% of the Earths surface. ... Water resources are sources of water that are useful or potentially useful to humans. ... In ecology, a biogeochemical cycle is a circuit where a nutrient moves back and forth between both biotic and abiotic components of ecosystems. ...

External Links

• Hydrologic Cycle from Earthscape
• Hydrologic Cycle from GROW
• United States Geological Survey Water Site