Water Cycle

Water Cycle

Water Cycle

The water cycle, also known as the hydrologic cycle or the hydrological 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, surface runoff, and subsurface flow. In doing so, the water goes through different forms: liquid, solid (ice) and vapor.

Water cycle, cycle that involves the continuous circulation of water in the Earth-atmosphere system. Of the many processes involved in the water cycle, the most important are evaporation, transpiration, condensation, precipitation, and runoff. Learn more about the water cycle in this article.

There is no definable start or finish to the water cycle. Water molecules move continuously among different compartments, or reservoirs, of the Earth's hydrosphere, by different physical processes. Water evaporates from the oceans, forms clouds, which precipitate and the water falls back to Earth. However, water does not necessarily cycle through each compartment in order. Before reaching the ocean, water may have evaporated, condensed, precipitated, and become runoff multiple times.

Precipitation is a vital component of how water moves through Earth’s water cycle, connecting the ocean, land, and atmosphere. Knowing where it rains, how much it rains and the character of the falling rain, snow or hail allows scientists to better understand precipitation’s impact on streams, rivers, surface runoff and groundwater.