Water cycle

Page semi-protected
Source: Wikipedia, the free encyclopedia.

A detailed diagram by the United States Geological Survey depicting the global water cycle. Inset on the lower right is the directionality of the movement of water between reservoirs. Directionality tends towards upwards movement through evapotranspiration and downward movement through gravity.

The water cycle, also known as the hydrologic cycle or the hydrological cycle, is a

precipitation, infiltration, surface runoff, and subsurface flow. In doing so, the water goes through different forms: liquid, solid (ice) and vapor. The ocean plays a key role in the water cycle as it is the source of 86% of global evaporation.[1]

The water cycle involves the exchange of energy, which leads to temperature changes. When water evaporates, it takes up energy from its surroundings and cools the environment. When it condenses, it releases energy and warms the environment. These heat exchanges influence climate.

The evaporative phase of the cycle purifies water, causing salts and other solids picked up during the cycle to be left behind, and then the condensation phase in the atmosphere replenishes the land with freshwater. The flow of liquid water and ice transports minerals across the globe. It is also involved in reshaping the geological features of the Earth, through processes including erosion and sedimentation. The water cycle is also essential for the maintenance of most life and ecosystems on the planet.


Part of a series on
Biogeochemical cycles
Water cycle
Carbon cycle
Nutrient cycle
Rock cycle
Marine cycle
Methane cycle
Other cycles
Related topics
Research groups

Description

Video of the Earth's water cycle (NASA)[2]

Overall process

Further information: Water distribution on Earth

The water cycle is powered from the energy emitted by the sun. This energy heats water in the ocean and seas. Water evaporates as water vapor into the

sublimates directly into water vapor. Evapotranspiration is water transpired from plants and evaporated from the soil. The water molecule H
2O has smaller molecular mass than the major components of the atmosphere, nitrogen (N
2) and oxygen (O
2) and hence is less dense. Due to the significant difference in density, buoyancy drives humid air higher. As altitude increases, air pressure decreases and the temperature drops (see Gas laws). The lower temperature causes water vapor to condense into tiny liquid water droplets which are heavier than the air, and which fall unless supported by an updraft. A huge concentration of these droplets over a large area in the atmosphere becomes visible as cloud, while condensation near ground level is referred to as fog
.

precipitation. Some precipitation falls as snow, hail, or sleet, and can accumulate in ice caps and glaciers, which can store frozen water for thousands of years. Most water falls as rain back into the ocean or onto land, where the water flows over the ground as surface runoff. A portion of this runoff enters rivers, with streamflow moving water towards the oceans. Runoff and water emerging from the ground (groundwater) may be stored as freshwater in lakes. Not all runoff flows into rivers; much of it soaks into the ground as infiltration. Some water infiltrates deep into the ground and replenishes aquifers, which can store freshwater for long periods of time. Some infiltration stays close to the land surface and can seep back into surface-water bodies (and the ocean) as groundwater discharge or be taken up by plants and transferred back to the atmosphere as water vapor by transpiration. Some groundwater finds openings in the land surface and emerges as freshwater springs. In river valleys and floodplains, there is often continuous water exchange between surface water and ground water in the hyporheic zone
. Over time, the water returns to the ocean, to continue the water cycle.

The ocean plays a key role in the water cycle. The ocean holds "97% of the total water on the planet; 78% of global precipitation occurs over the ocean, and it is the source of 86% of global evaporation".[1]

Processes leading to movements and phase changes in water

Important physical processes within the water cycle include the following (in alphabetical order):

Residence times

Average reservoir residence times[13]
Reservoir Average residence time
Antarctica 20,000 years
Oceans 3,200 years
Glaciers 20 to 100 years
Seasonal snow cover 2 to 6 months
Soil moisture 1 to 2 months
Groundwater: shallow 100 to 200 years
Groundwater: deep 10,000 years
Lakes (see lake retention time) 50 to 100 years
Rivers 2 to 6 months
Atmosphere 9 days

The

residence time
of a reservoir within the hydrologic cycle is the average time a water molecule will spend in that reservoir (see adjacent table). It is a measure of the average age of the water in that reservoir.

Groundwater can spend over 10,000 years beneath Earth's surface before leaving.[14] Particularly old groundwater is called fossil water. Water stored in the soil remains there very briefly, because it is spread thinly across the Earth, and is readily lost by evaporation, transpiration, stream flow, or groundwater recharge. After evaporating, the residence time in the atmosphere is about 9 days before condensing and falling to the Earth as precipitation.

The major ice sheets – Antarctica and Greenland – store ice for very long periods. Ice from Antarctica has been reliably dated to 800,000 years before present, though the average residence time is shorter.[15]

In hydrology, residence times can be estimated in two ways.[citation needed] The more common method relies on the principle of conservation of mass (water balance) and assumes the amount of water in a given reservoir is roughly constant. With this method, residence times are estimated by dividing the volume of the reservoir by the rate by which water either enters or exits the reservoir. Conceptually, this is equivalent to timing how long it would take the reservoir to become filled from empty if no water were to leave (or how long it would take the reservoir to empty from full if no water were to enter).

An alternative method to estimate residence times, which is gaining in popularity for dating groundwater, is the use of isotopic techniques. This is done in the subfield of isotope hydrology.

Water in storage

Further information: Water resources and Water distribution on Earth
Water cycle showing human influences and major pools (storages) and fluxes.[16]

The water cycle describes the processes that drive the movement of water throughout the hydrosphere. However, much more water is "in storage" (or in "pools") for long periods of time than is actually moving through the cycle. The storehouses for the vast majority of all water on Earth are the oceans. It is estimated that of the 1,386,000,000 km3 of the world's water supply, about 1,338,000,000 km3 is stored in oceans, or about 97%. It is also estimated that the oceans supply about 90% of the evaporated water that goes into the water cycle.[17] The Earth's ice caps, glaciers, and permanent snowpack stores another 24,064,000 km3 accounting for only 1.7% of the planet's total water volume. However, this quantity of water is 68.7% of all freshwater on the planet.[18]

Changes caused by humans

Extreme weather (heavy rains, droughts, heat waves) is one consequence of a changing water cycle due to global warming. These events will be progressively more common as the Earth warms more and more.[19]: Figure SPM.6 
Predicted changes in average soil moisture for a scenario of 2°C global warming. This can disrupt agriculture and ecosystems. A reduction in soil moisture by one standard deviation means that average soil moisture will approximately match the ninth driest year between 1850 and 1900 at that location.

Water cycle intensification due to climate change

Main articles: Effects of climate change on the water cycle and Effects of climate change on oceans

Since the middle of the 20th century, human-caused climate change has resulted in observable changes in the global water cycle.[20]: 85  The IPCC Sixth Assessment Report in 2021 predicted that these changes will continue to grow significantly at the global and regional level.[20]: 85  These findings are a continuation of scientific consensus expressed in the IPCC Fifth Assessment Report from 2007 and other special reports by the Intergovernmental Panel on Climate Change which had already stated that the water cycle will continue to intensify throughout the 21st century.[21]

This section is an excerpt from Effects of climate change on the water cycle.[edit]

The

ocean circulation. The warming of our planet is expected to be accompanied by changes in the water cycle for various reasons.[23] For example, a warmer atmosphere can contain more water vapor which has effects on evaporation and rainfall
.

The underlying cause of the intensifying water cycle is the increased amount of

Clausius-Clapeyron equation
.

The strength of the water cycle and its changes over time are of considerable interest, especially as the climate changes.[25] The hydrological cycle is a system whereby the evaporation of moisture in one place leads to precipitation (rain or snow) in another place. For example, evaporation always exceeds precipitation over the oceans. This allows moisture to be transported by the atmosphere from the oceans onto land where precipitation exceeds evapotranspiration. The runoff from the land flows into streams and rivers and discharges into the ocean, which completes the global cycle.[25] The water cycle is a key part of Earth's energy cycle through the evaporative cooling at the surface which provides latent heat to the atmosphere, as atmospheric systems play a primary role in moving heat upward.[25]

Changes due to other human activities

impervious surfaces and surface runoff

Human activities, other than those that lead to global warming from greenhouse gas emissions, can also alter the water cycle. The IPCC Sixth Assessment Report stated that there is "abundant evidence that changes in land use and land cover alter the water cycle globally, regionally and locally, by changing precipitation, evaporation, flooding, groundwater, and the availability of freshwater for a variety of uses".[26]: 1153 

Examples for such

land use changes are converting fields to urban areas or clearing forests. Such changes can affect the ability of soils to soak up surface water. Deforestation has local as well as regional effects. For example it reduces soil moisture, evaporation and rainfall at the local level. Furthermore, deforestation causes regional temperature changes that can affect rainfall patterns.[26]
: 1153 

Aquifer drawdown or overdrafting and the pumping of fossil water increase the total amount of water in the hydrosphere. This is because the water that was originally in the ground has now become available for evaporation as it is now in contact with the atmosphere.[26]: 1153 

Related processes

Biogeochemical cycling

While the water cycle is itself a

river system to the Gulf of Mexico. Runoff also plays a part in the carbon cycle, again through the transport of eroded rock and soil.[30]

Slow loss over geologic time

Main article: Atmospheric escape

The hydrodynamic wind within the upper portion of a planet's atmosphere allows light chemical elements such as

planetary wind.[31] Planets with hot lower atmospheres could result in humid upper atmospheres that accelerate the loss of hydrogen.[32]

Historical interpretations

Floating land mass

In ancient times, it was widely thought that the land mass floated on a body of water, and that most of the water in rivers has its origin under the earth. Examples of this belief can be found in the works of Homer (c. 800 BCE).

Hebrew Bible

In the

King Solomon, son of David and Bathsheba, "three thousand years ago,[33] there is some agreement that the time period is 962–922 BCE.[34] Furthermore, it was also observed that when the clouds were full, they emptied rain on the earth (Ecclesiastes 11:3). In addition, during 793–740 BCE a Hebrew prophet, Amos, stated that water comes from the sea and is poured out on the earth (Amos 5:8).[35]

In the Biblical Book of Job, dated between 7th and 2nd centuries BCE,[34] there is a description of precipitation in the hydrologic cycle,[33] "For he maketh small the drops of water: they pour down rain according to the vapour thereof; which the clouds do drop and distil upon man abundantly" (Job 36:27-28).

Understanding of precipitation and percolation

In the

Adityahridayam (a devotional hymn to the Sun God) of Ramayana, a Hindu epic dated to the 4th century BCE, it is mentioned in the 22nd verse that the Sun heats up water and sends it down as rain. By roughly 500 BCE, Greek scholars were speculating that much of the water in rivers can be attributed to rain. The origin of rain was also known by then. These scholars maintained the belief, however, that water rising up through the earth contributed a great deal to rivers. Examples of this thinking included Anaximander (570 BCE) (who also speculated about the evolution of land animals from fish[36]) and Xenophanes of Colophon (530 BCE).[37] Warring States period Chinese scholars such as Chi Ni Tzu (320 BCE) and Lu Shih Ch'un Ch'iu (239 BCE) had similar thoughts.[38]

The idea that the water cycle is a closed cycle can be found in the works of

of Earth in his Lunheng but was dismissed by his contemporaries.[41]

Up to the time of the Renaissance, it was wrongly assumed that precipitation alone was insufficient to feed rivers, for a complete water cycle, and that underground water pushing upwards from the oceans were the main contributors to river water.

Bartholomew of England held this view (1240 CE), as did Leonardo da Vinci (1500 CE) and Athanasius Kircher
(1644 CE).

Discovery of the correct theory

The first published thinker to assert that rainfall alone was sufficient for the maintenance of rivers was Bernard Palissy (1580 CE), who is often credited as the discoverer of the modern theory of the water cycle. Palissy's theories were not tested scientifically until 1674, in a study commonly attributed to Pierre Perrault. Even then, these beliefs were not accepted in mainstream science until the early nineteenth century.[42]

See also

References

  1. ^ a b "Water Cycle | Science Mission Directorate". science.nasa.gov. Archived from the original on 2018-01-15. Retrieved 2018-01-15.
  2. ^ NASA (2012-01-12). "NASA Viz: The Water Cycle: Following The Water". svs.gsfc.nasa.gov. Retrieved 2022-09-28.
  3. ^ "advection". National Snow and Ice Data Center. Archived from the original on 2018-01-16. Retrieved 2018-01-15.
  4. ^ "Atmospheric River Information Page". NOAA Earth System Research Laboratory.
  5. ^ "condensation". National Snow and Ice Data Center. Archived from the original on 2018-01-16. Retrieved 2018-01-15.
  6. ^ "evaporation". National Snow and Ice Data Center. Archived from the original on 2018-01-16. Retrieved 2018-01-15.
  7. ^ a b "The Water Cycle". Dr. Art's Guide to Planet Earth. Archived from the original on 2011-12-26. Retrieved 2006-10-24.{{cite web}}: CS1 maint: unfit URL (link)
  8. ^ a b "Salinity | Science Mission Directorate". science.nasa.gov. Archived from the original on 2018-01-15. Retrieved 2018-01-15.
  9. ^ "Hydrologic Cycle". Northwest River Forecast Center. NOAA. Archived from the original on 2006-04-27. Retrieved 2006-10-24.
  10. S2CID 4467297
    .
  11. ^ "precipitation". National Snow and Ice Data Center. Archived from the original on 2018-01-16. Retrieved 2018-01-15.
  12. ^ a b "Estimated Flows of Water in the Global Water Cycle". www3.geosc.psu.edu. Archived from the original on 2017-11-07. Retrieved 2018-01-15.
  13. ^ "Chapter 8: Introduction to the Hydrosphere". 8(b) the Hydrologic Cycle. Archived from the original on 2016-01-26. Retrieved 2006-10-24. {{cite book}}: |website= ignored (help)
  14. ISSN 0094-8276
    .
  15. S2CID 30125808
    .
  16. S2CID 195214876
    .
  17. ^ "The Water Cycle summary". USGS Water Science School. Archived from the original on 2018-01-16. Retrieved 2018-01-15.
  18. ^ Water Science School. "Ice, Snow, and Glaciers and the Water Cycle". USGS. US Department of the Interior. Retrieved October 17, 2022.
  19. ^ IPCC, 2021: Summary for Policymakers. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, US, pp. 3−32, doi:10.1017/9781009157896.001.
  20. ^ a b Arias, P.A., N. Bellouin, E. Coppola, R.G. Jones, G. Krinner, J. Marotzke, V. Naik, M.D. Palmer, G.-K. Plattner, J. Rogelj, M. Rojas, J. Sillmann, T. Storelvmo, P.W. Thorne, B. Trewin, K. Achuta Rao, B. Adhikary, R.P. Allan, K. Armour, G. Bala, R. Barimalala, S. Berger, J.G. Canadell, C. Cassou, A. Cherchi, W. Collins, W.D. Collins, S.L. Connors, S. Corti, F. Cruz, F.J. Dentener, C. Dereczynski, A. Di Luca, A. Diongue Niang, F.J. Doblas-Reyes, A. Dosio, H. Douville, F. Engelbrecht, V.  Eyring, E. Fischer, P. Forster, B. Fox-Kemper, J.S. Fuglestvedt, J.C. Fyfe, et al., 2021: Technical Summary. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, US, pp. 33−144. doi:10.1017/9781009157896.002.
  21. ^ Alley, Richard; et al. (February 2007). "Climate Change 2007: The Physical Science Basis" (PDF). International Panel on Climate Change. Archived from the original (PDF) on February 3, 2007.
  22. ^ a b Douville, H., K. Raghavan, J. Renwick, R.P. Allan, P.A. Arias, M. Barlow, R. Cerezo-Mota, A. Cherchi, T.Y. Gan, J. Gergis, D.  Jiang, A.  Khan, W.  Pokam Mba, D.  Rosenfeld, J. Tierney, and O.  Zolina, 2021: Water Cycle Changes. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I  to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, US, pp. 1055–1210, doi:10.1017/9781009157896.010.
  23. ^ a b IPCC (2013). Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press.
  24. ^ Vahid, Alavian; Qaddumi, Halla Maher; Dickson, Eric; Diez, Sylvia Michele; Danilenko, Alexander V.; Hirji, Rafik Fatehali; Puz, Gabrielle; Pizarro, Carolina; Jacobsen, Michael (November 1, 2009). "Water and climate change: understanding the risks and making climate-smart investment decisions". Washington, DC: World Bank. pp. 1–174. Archived from the original on 2017-07-06.
  25. ^
    doi:10.1175/2011JCLI4171.1. Text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License
  26. ^ a b c Douville, H., K. Raghavan, J. Renwick, R.P. Allan, P.A. Arias, M. Barlow, R. Cerezo-Mota, A. Cherchi, T.Y. Gan, J. Gergis, D.  Jiang, A.  Khan, W.  Pokam Mba, D.  Rosenfeld, J. Tierney, and O.  Zolina, 2021: Water Cycle Changes. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I  to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, US, pp. 1055–1210, doi:10.1017/9781009157896.010.
  27. ^ "Biogeochemical Cycles". The Environmental Literacy Council. Archived from the original on 2015-04-30. Retrieved 2006-10-24.
  28. ^ "Phosphorus Cycle". The Environmental Literacy Council. Archived from the original on 2016-08-20. Retrieved 2018-01-15.
  29. ^ "Nitrogen and the Hydrologic Cycle". Extension Fact Sheet. Ohio State University. Archived from the original on 2006-09-01. Retrieved 2006-10-24.
  30. ^ "The Carbon Cycle". Earth Observatory. NASA. 2011-06-16. Archived from the original on 2006-09-28. Retrieved 2006-10-24.
  31. ^ Nick Strobel (June 12, 2010). "Planetary Science". Archived from the original on September 17, 2010. Retrieved September 28, 2010.
  32. ISBN 978-3-527-40671-5. Retrieved 2009-05-05.[permanent dead link
    ]
  33. ^ a b c Morris, Henry M. (1988). Science and the Bible (Trinity Broadcasting Network ed.). Chicago, IL: Moody Press. p. 15.
  34. ^
    ISBN 978-0195046458
    .
  35. ISBN 9780805440317
    .
  36. ^ Kazlev, M.Alan. "Palaeos: History of Evolution and Paleontology in science, philosophy, religion, and popular culture : Pre 19th Century". Archived from the original on 2014-03-02.
  37. ^ James H. Lesher. "Xenophanes' Scepticism" (PDF). pp. 9–10. Archived from the original (PDF) on 2013-07-28. Retrieved 2014-02-26.
  38. ISBN 9781901502572
    – via Google Books.
  39. ISBN 9781499461275
    .
  40. ISBN 9781139460019
    .
  41. ISBN 0-521-05801-5
    .
  42. ^ James C.I. Dodge. Concepts of the hydrological Cycle. Ancient and modern (PDF). International Symposium OH
    2     'Origins and History of Hydrology', Dijon, May 9–11, 2001. Archived (PDF) from the original on 2014-10-11. Retrieved 2014-02-26.

External links

Wikimedia Commons has media related to Water cycle.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Water_cycle&oldid=1219594710"