Editing Water cycle (section)

{{for|the bicycle-like watercraft|hydrocycle}}
{{Short description|Biogeochemical cycle for movement of water on Earth}}
{{pp|small=yes}}
[[File:USGS WaterCycle English ONLINE 20221013.png|thumb|upright=1.35|A detailed diagram depicting the global water cycle. The direction of movement of water between reservoirs tends towards upwards movement through [[evapotranspiration]] and downward movement through [[gravity]]. The diagram also shows how human water use impacts where water is stored and how it moves.<ref>{{Cite web |title=The Water Cycle (PNG) {{!}} U.S. Geological Survey |url=https://www.usgs.gov/media/images/water-cycle-png |access-date=2024-04-24 |website=www.usgs.gov|date=13 October 2022 }}</ref>]]
The '''water cycle''' (or '''hydrologic cycle''' or '''hydrological cycle''') is a [[biogeochemical cycle]] that involves the continuous movement of [[water]] on, above and below the surface of the [[Earth]] across different reservoirs. The mass of water on Earth remains fairly constant over time.<ref>{{Cite web |title=Water may change phases, but the amount always remains constant |url=https://ny1.com/nyc/all-boroughs/weather/2021/11/19/the-water-cycle- |access-date=2025-05-01 |website=ny1.com |language=en}}</ref> However, the partitioning of the water into the major reservoirs of [[ice]], [[fresh water]], [[Saline water|salt water]] and [[Atmosphere|atmospheric water]] is variable and depends on [[Climate|climatic variables]]. The water moves from one reservoir to another, such as from river to [[ocean]], or from the ocean to the atmosphere due to a variety of physical and chemical processes. The processes that drive these movements, or [[Flux (biology)|fluxes]], are [[evaporation]], [[transpiration]], [[condensation]], [[Precipitation (meteorology)|precipitation]], [[Sublimation (phase transition)|sublimation]], [[Infiltration (hydrology)|infiltration]], [[surface runoff]], and subsurface flow. In doing so, the water goes through different phases: liquid, solid ([[ice]]) and [[Water vapor|vapor]]. The ocean plays a key role in the water cycle as it is the source of 86% of global evaporation.<ref name=":4">{{Cite web |title=Water Cycle {{!}} Science Mission Directorate |url=https://science.nasa.gov/earth-science/oceanography/ocean-earth-system/ocean-water-cycle |url-status=live |archive-url=https://web.archive.org/web/20180115065559/https://science.nasa.gov/earth-science/oceanography/ocean-earth-system/ocean-water-cycle |archive-date=2018-01-15 |access-date=2018-01-15 |website=science.nasa.gov |language=en}}</ref>

The water cycle is driven by energy exchanges in the form of heat transfers between different phases. The energy released or absorbed during a phase change can result in [[temperature]] changes.<ref>{{Cite web |title=Endothermic and exothermic processes {{!}} EBSCO Research Starters |url=https://www.ebsco.com/research-starters/chemistry/endothermic-and-exothermic-processes |access-date=2025-05-01 |website=www.ebsco.com |language=en}}</ref> Heat is absorbed as water transitions from the liquid to the vapor phase through evaporation. This heat is also known as the latent heat of vaporization.<ref>{{Citation |last=Kirkham |first=M. B. |title=Chapter 3 - Structure and Properties of Water |date=2014-01-01 |work=Principles of Soil and Plant Water Relations (Second Edition) |pages=27–40 |editor-last=Kirkham |editor-first=M. B. |url=https://linkinghub.elsevier.com/retrieve/pii/B9780124200227000033 |access-date=2025-05-01 |place=Boston |publisher=Academic Press |doi=10.1016/b978-0-12-420022-7.00003-3 |isbn=978-0-12-420022-7|url-access=subscription }}</ref> Conversely, when water condenses or melts from solid ice it releases energy and heat. On a global scale, water plays a critical role in transferring heat from the tropics to the poles via ocean circulation.<ref>{{Cite web |title=Ocean currents - Atmosphere and climate - Edexcel - GCSE Geography Revision - Edexcel |url=https://www.bbc.co.uk/bitesize/guides/zpykxsg/revision/2#:~:text=Heat%20is%20transferred%20by%20warm,with%20the%20general%20atmospheric%20circulation. |access-date=2025-05-01 |website=BBC Bitesize |language=en-GB}}</ref>

The evaporative phase of the cycle also acts as a purification process by separating water molecules from salts and other particles that are present in its liquid phase.<ref>{{Cite web |date=2019-09-24 |title=7.1: Evaporation |url=https://chem.libretexts.org/Bookshelves/General_Chemistry/Book:_Structure_and_Reactivity_in_Organic_Biological_and_Inorganic_Chemistry_(Schaller)/Structure_and_Reactivity_in_Organic_Biological_and_Inorganic_Chemistry_II:_Practical_Aspects_of_Structure_-_Purification_and_Spectroscopy/07:_Purification_of_Molecular_Compounds/7.01:_Evaporation |access-date=2025-05-01 |website=Chemistry LibreTexts |language=en}}</ref> The condensation phase in the atmosphere replenishes the land with freshwater. The flow of liquid water transports minerals across the globe. It also reshapes the geological features of the Earth, through processes of weathering, [[erosion]], and deposition. The water cycle is also essential for the maintenance of most life and [[Ecosystem|ecosystems]] on the planet.

[[Human impact on the environment|Human actions]] are greatly affecting the water cycle. Activities such as [[deforestation]], [[urbanization]], and the extraction of [[groundwater]] are altering natural landscapes ([[Land use change|land use changes]]) all have an effect on the water cycle.<ref name=":22" />{{rp|1153}} On top of this, [[climate change]] is leading to an [[intensification of the water cycle]]. Research has shown that global warming is causing shifts in precipitation patterns, increased frequency of [[extreme weather]] events, and changes in the timing and intensity of rainfall.<ref name=":0" />{{rp|85}} These water cycle changes affect [[Ecosystem|ecosystems]], [[Water scarcity|water availability]], agriculture, and human societies.