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, freshwater saline water and atmosperic water is variable depending on a wide range of climate 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.