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Water Cycle Short Essay Examples


Water Cycle, also known as hydrologic cycle, is a process that is constantly recycling the Earth's supply of water. This is important because humans, animals, and plants all need water to survive. It is controlled by the sun, which produces energy in the form of heat. This heat energy causes the water in the world's oceans, lakes, etc. to warm and evaporate. As the water is heated, it changes its phase from liquid to gas. This gas is called water vapor and this process is called evaporation. When plants give off water vapor, it’s called transpiration. When water evaporates, it rises into the cooler air, collects, and forms clouds. There, the water vapor molecules cool down and change back into liquid water. This is called condensation. As more and more water vapor cools into the clouds, the water droplets that form the clouds become larger and larger. When the swirling winds in the atmosphere can no longer hold them up, the droplets fall from the sky and precipitation is the term for the falling, condensed water molecules, which come down as rain, snow, sleet, or hail depending on conditions in the atmosphere. When water falls to the Earth, the water seeps into the soil because of the force of gravity. This seeping is called infiltration. Or the water flows over the land and into bodies of water, such as rivers and lakes.

Evaporation (the importance)

The water cycle is powered from solar energy. 86% of the global evaporation occurs from the oceans, reducing their temperature by evaporative cooling. Without the cooling effect of evaporation the greenhouse effect would lead to a much higher surface temperature of 67 Ð'oC, and a warmer planet.

Most of the solar energy warms tropical seas. After evaporating, water vapor rises into the atmosphere and is carried by winds away from the tropics. Most of this vapor condenses as rain in the Intertropical convergence zone, also known as the ITCZ, releasing latent heat that warms the air. This in turn drives the atmospheric circulation. (

Impacts of Temperature changes in Water Cycle

Increasing temperature increases the rates of evaporation and ice melting, and causes sea level to rise. Like in Florida for example, where sea level rose to 4.7m (Noting that during the last glaciations sea level was a full 100 m lower than it is today). Severe droughts, like in the Sahel in Africa, and glacier melting like in the French Alps and Alaska are caused by small changes in the geographical distribution of water that are in turn caused by changes in temperature. Moreover, there will be an increased river flow of freshwater from land to the ocean, and especially to the Arctic Ocean, as more and more of the ice caps on land melt. This flow of water will place a less dense, freshwater "cap" on the surface water of the ocean, and could prevent sinking of cold, salty water ("deep water formation") that drives ocean currents. ( ent /lectures/kling /rainforest/rainforest.html)

Human Impacts on Terrestrial Water Cycle

Water cycle plays a central role in the climate, ecology, and biogeochemistry of the planet. Increasing historical evidence for the influence of greenhouse warming on recent climate, and modeling projections into the future, highlight changes to the land based water cycle as a major global change issue (Houghton et al. 1995,Watson et al. 1996, SGCR 1999). Disturbance of the water cycle has received significant attention with respect to atmosphere exchanges, plant physiology, net primary production, and the cycling of major nutrients (Foley et al. 1996, Sellers et al. 1996, McGuire et al. 1997).

Major Agents of Anthropogenic Change and its Impact on the Global Water Cycle

The expansion of global water use requires the stabilization of continental runoff and diversion of water from one part of the hydrologic cycle to another. These changes can be translated into particular storage changes as well as reductions or increases in natural hydrological fluxes. The following are the major agents of anthropogenic change and their potential impacts on the terrestrial water system.

Aquifer mining

In most dry regions, where surface water is insufficient, mined fossil groundwater is the main water resource for irrigation and other uses. Natural rates of water recharge to the aquifer are very low. Therefore, when water is extracted from such groundwater pools, most will be transferred from the aquifer to the atmosphere. This transfer represents both a depletion of continental storage and at least a temporary increase in atmospheric water vapor through the enhanced evaporative flux.

Surface water diversion and changes in internally draining lake volumes

Diversion of surface waters for irrigation in the internally draining basins of arid regions


The water cycle, also known as the hydrological cycle or the hydrologic 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.

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 which then 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.


The sun, which drives the water cycle, heats water in oceans and seas. Water evaporates as water vapor into the air. Ice and snow can sublimate directly into water vapour. Evapotranspiration is water transpired from plants and evaporated from the soil. The water vapour molecule H
2O has less density compared to the major components of the atmosphere, nitrogen and oxygen, N
2 and O
2. Due to the significant difference in molecular mass, water vapor in gas form gains height in open air as a result of buoyancy. However, as altitude increases, air pressure decreases and the temperature drops (see Gas laws). The lowered temperature causes water vapour to condense into a tiny liquid water droplet which is heavier than the air, such that it falls unless supported by an updraft. A huge concentration of these droplets over a large space up in the atmosphere become visible as cloud. Fog is formed if the water vapour condenses near ground level, as a result of moist air and cool air collision or an abrupt reduction in air pressure. Air currents move water vapour around the globe, cloud particles collide, grow, and fall out of the upper atmospheric layers as precipitation. Some precipitation falls as snow or hail, sleet, and can accumulate as ice caps and glaciers, which can store frozen water for thousands of years. Most water falls back into the oceans or onto land as rain, where the water flows over the ground as surface runoff. A portion of runoff enters rivers in valleys in the landscape, 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. Some groundwater finds openings in the land surface and comes out 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.


Condensed water vapor that falls to the Earth's surface. Most precipitation occurs as rain, but also includes snow, hail, fog drip, graupel, and sleet.[1] Approximately 505,000 km3 (121,000 cu mi) of water falls as precipitation each year, 398,000 km3 (95,000 cu mi) of it over the oceans.[2][better source needed] The rain on land contains 107,000 km3 (26,000 cu mi) of water per year and a snowing only 1,000 km3 (240 cu mi).[3] 78% of global precipitation occurs over the ocean.[4]
Canopy interception
The precipitation that is intercepted by plant foliage eventually evaporates back to the atmosphere rather than falling to the ground.
The runoff produced by melting snow.
The variety of ways by which water moves across the land. This includes both surface runoff and channel runoff. As it flows, the water may seep into the ground, evaporate into the air, become stored in lakes or reservoirs, or be extracted for agricultural or other human uses.
The flow of water from the ground surface into the ground. Once infiltrated, the water becomes soil moisture or groundwater.[5] A recent global study using water stable isotopes, however, shows that not all soil moisture is equally available for groundwater recharge or for plant transpiration.[6]
Subsurface flow
The flow of water underground, in the vadose zone and aquifers. Subsurface water may return to the surface (e.g. as a spring or by being pumped) or eventually seep into the oceans. Water returns to the land surface at lower elevation than where it infiltrated, under the force of gravity or gravity induced pressures. Groundwater tends to move slowly and is replenished slowly, so it can remain in aquifers for thousands of years.
The transformation of water from liquid to gas phases as it moves from the ground or bodies of water into the overlying atmosphere.[7] The source of energy for evaporation is primarily solar radiation. Evaporation often implicitly includes transpiration from plants, though together they are specifically referred to as evapotranspiration. Total annual evapotranspiration amounts to approximately 505,000 km3 (121,000 cu mi) of water, 434,000 km3 (104,000 cu mi) of which evaporates from the oceans.[2] 86% of global evaporation occurs over the ocean.[4]
The state change directly from solid water (snow or ice) to water vapor by passing the liquid state.[8]
This refers to changing of water vapor directly to ice.
The movement of water through the atmosphere.[9] Without advection, water that evaporated over the oceans could not precipitate over land.
The transformation of water vapor to liquid water droplets in the air, creating clouds and fog.[10]
The release of water vapor from plants and soil into the air.
Water flows vertically through the soil and rocks under the influence of gravity.
Plate tectonics
Water enters the mantle via subduction of oceanic crust. Water returns to the surface via volcanism.

The water cycle involves many of these processes.

ReservoirAverage residence time
Antarctica20,000 years
Oceans3,200 years
Glaciers20 to 100 years
Seasonal snow cover2 to 6 months
Soil moisture1 to 2 months
Groundwater: shallow100 to 200 years
Groundwater: deep10,000 years
Lakes (see lake retention time)50 to 100 years
Rivers2 to 6 months
Atmosphere9 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. 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.[12]

In hydrology, residence times can be estimated in two ways. The more common method relies on the principle of conservation of mass 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.

Changes over time

The water cycle describes the processes that drive the movement of water throughout the hydrosphere. However, much more water is "in storage" 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 332,500,000 mi3 (1,386,000,000 km3) of the world's water supply, about 321,000,000 mi3 (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.[13]

During colder climatic periods, more ice caps and glaciers form, and enough of the global water supply accumulates as ice to lessen the amounts in other parts of the water cycle. The reverse is true during warm periods. During the last ice age, glaciers covered almost one-third of Earth's land mass with the result being that the oceans were about 122 m (400 ft) lower than today. During the last global "warm spell," about 125,000 years ago, the seas were about 5.5 m (18 ft) higher than they are now. About three million years ago the oceans could have been up to 50 m (165 ft) higher.[13]

The scientific consensus expressed in the 2007 Intergovernmental Panel on Climate Change (IPCC) Summary for Policymakers is for the water cycle to continue to intensify throughout the 21st century, though this does not mean that precipitation will increase in all regions.[14] In subtropical land areas — places that are already relatively dry — precipitation is projected to decrease during the 21st century, increasing the probability of drought. The drying is projected to be strongest near the poleward margins of the subtropics (for example, the Mediterranean Basin, South Africa, southern Australia, and the Southwestern United States). Annual precipitation amounts are expected to increase in near-equatorial regions that tend to be wet in the present climate, and also at high latitudes. These large-scale patterns are present in nearly all of the climate model simulations conducted at several international research centers as part of the 4th Assessment of the IPCC. There is now ample evidence that increased hydrologic variability and change in climate has and will continue to have a profound impact on the water sector through the hydrologic cycle, water availability, water demand, and water allocation at the global, regional, basin, and local levels.[15] Research published in 2012 in Science based on surface ocean salinity over the period 1950 to 2000 confirm this projection of an intensified global water cycle with salty areas becoming more saline and fresher areas becoming more fresh over the period:[16]

Fundamental thermodynamics and climate models suggest that dry regions will become drier and wet regions will become wetter in response to warming. Efforts to detect this long-term response in sparse surface observations of rainfall and evaporation remain ambiguous. We show that ocean salinity patterns express an identifiable fingerprint of an intensifying water cycle. Our 50-year observed global surface salinity changes, combined with changes from global climate models, present robust evidence of an intensified global water cycle at a rate of 8 ± 5% per degree of surface warming. This rate is double the response projected by current-generation climate models and suggests that a substantial (16 to 24%) intensification of the global water cycle will occur in a future 2° to 3° warmer world.[17]

An instrument carried by the SAC-D satellite Aquarius, launched in June, 2011, measured global sea surface salinity.[18][19]

Glacial retreat is also an example of a changing water cycle, where the supply of water to glaciers from precipitation cannot keep up with the loss of water from melting and sublimation. Glacial retreat since 1850 has been extensive.[20]

Human activities that alter the water cycle include:

Effects on climate

The water cycle is powered from solar energy. 86% of the global evaporation occurs from the oceans, reducing their temperature by evaporative cooling.[21] Without the cooling, the effect of evaporation on the greenhouse effect would lead to a much higher surface temperature of 67 °C (153 °F), and a warmer planet.[citation needed]

Aquifer drawdown or overdrafting and the pumping of fossil water increases the total amount of water in the hydrosphere, and has been postulated to be a contributor to sea-level rise.[22]

Effects on biogeochemical cycling

While the water cycle is itself a biogeochemical cycle, flow of water over and beneath the Earth is a key component of the cycling of other biogeochemicals.[23] Runoff is responsible for almost all of the transport of erodedsediment and phosphorus from land to waterbodies.[24] The salinity of the oceans is derived from erosion and transport of dissolved salts from the land. Cultural eutrophication of lakes is primarily due to phosphorus, applied in excess to agricultural fields in fertilizers, and then transported overland and down rivers. Both runoff and groundwater flow play significant roles in transporting nitrogen from the land to waterbodies.[25] The dead zone at the outlet of the Mississippi River is a consequence of nitrates from fertilizer being carried off agricultural fields and funnelled down the 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.[26]

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 Hydrogen to move up to the exobase, the lower limit of the exosphere, where the gases can then reach escape velocity, entering outer space without impacting other particles of gas. This type of gas loss from a planet into space is known as planetary wind.[27] Planets with hot lower atmospheres could result in humid upper atmospheres that accelerate the loss of hydrogen.[28]

History of hydrologic cycle theory

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 (circa 800 BCE).

Source of rain

In the ancient near east, Hebrew scholars observed that even though the rivers ran into the sea, the sea never became full (Ecclesiastes 1:7). Some scholars conclude that the water cycle was described completely during this time in this passage: "The wind goeth toward the south, and turneth about unto the north; it whirleth about continually, and the wind returneth again according to its circuits. All the rivers run into the sea, yet the sea is not full; unto the place from whence the rivers come, thither they return again" (Ecclesiastes 1:6-7, KJV).[29] Scholars are not in agreement as to the date of Ecclesiastes, though most scholars point to a date during the time of Solomon, the son of David and Bathsheba, "three thousand years ago,[29] there is some agreement that the time period is 962-922 BCE.[30] 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 BC a Hebrew prophet, Amos, stated that water comes from the sea and is poured out on the earth (Amos 5:8, 9:6).[31]

Precipitation and percolation

In the Adityahridayam (a devotional hymn to the Sun God) of Ramayana, a Hindu epic dated to the 4th century BC, 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[32]) and Xenophanes of Colophon (530 BCE).[33] Chinese scholars such as Chi Ni Tzu (320 BC) and Lu Shih Ch'un Ch'iu (239 BCE) had similar thoughts.[34] The idea that the water cycle is a closed cycle can be found in the works of Anaxagoras of Clazomenae (460 BCE) and Diogenes of Apollonia (460 BCE). Both Plato (390 BCE) and Aristotle (350 BCE) speculated about percolation as part of the water cycle.

Precipitation alone

In the Biblical Book of Job, dated between 7th and 2nd centuries BCE,[35] there is a description of precipitation in the hydrologic cycle,[36] "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, KJV).

Up to the time of the Renaissance, it was thought 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).

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.[37]

See also


  1. ^"precipitation | National Snow and Ice Data Center". Retrieved 2018-01-15. 
  2. ^ abDr. Art's Guide to Planet Earth. The Water Cycle. Retrieved on 2006-10-24.
  3. ^"Estimated Flows of Water in the Global Water Cycle". Retrieved 2018-01-15. 
  4. ^ ab"Salinity | Science Mission Directorate". Retrieved 2018-01-15. 
  5. ^National Weather Service Northwest River Forecast Center. Hydrologic Cycle. Retrieved on 2006-10-24.
  6. ^Evaristo, Jaivime; Jasechko, Scott; McDonnell, Jeffrey J. (2015-09-03). "Global separation of plant transpiration from groundwater and streamflow". Nature. NPG. 525 (7567): 91–94. Bibcode:2015Natur.525...91E. doi:10.1038/nature14983. ISSN 0028-0836. PMID 26333467. (Subscription required (help)). 
  7. ^"evaporation | National Snow and Ice Data Center". Retrieved 2018-01-15. 
  8. ^"sublimation | National Snow and Ice Data Center". Retrieved 2018-01-15. 
  9. ^"advection | National Snow and Ice Data Center". Retrieved 2018-01-15. 
  10. ^"condensation | National Snow and Ice Data Center". Retrieved 2018-01-15. 
  11. ^ CHAPTER 8: Introduction to the Hydrosphere. Retrieved on 2006-10-24.
  12. ^Jouzel, J.; Masson-Delmotte, V.; Cattani, O.; Dreyfus, G.; Falourd, S.; Hoffmann, G.; Minster, B.; Nouet, J.; Barnola, J. M. (2007-08-10). "Orbital and millennial Antarctic climate variability over the past 800,000 years". Science. 317 (5839): 793–796. Bibcode:2007Sci...317..793J. doi:10.1126/science.1141038. ISSN 1095-9203. PMID 17615306. 
  13. ^ abUSGS, Howard Perlman,. "The Water Cycle summary, USGS Water Science School". Retrieved 2018-01-15. 
  14. ^"Climate Change 2007: The Physical Science Basis"(PDF). INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE. February 2007. Archived from the original(PDF) on February 3, 2007. 
  15. ^Vahid, Alavian,; Maher, Qaddumi, Halla; Eric, Dickson,; Michele, Diez, Sylvia; V., Danilenko, Alexander; Fatehali, Hirji, Rafik; Gabrielle, Puz,; Carolina, Pizarro,; Michael, Jacobsen, (2009-11-01). "Water and climate change : understanding the risks and making climate-smart investment decisions". Washington, DC: World Bank: pp. xv. 
  16. ^Gillis, Justin (2012-04-26). "Study Hints at Greater Threat of Extreme Weather". The New York Times. ISSN 0362-4331. Retrieved 2018-01-15. 
  17. ^Paul J. Durack; Susan E. Wijffels & Richard J. Matear (27 April 2012). "Ocean Salinities Reveal Strong Global Water Cycle Intensification During 1950 to 2000". Science. 336 (6080): 455–458. Bibcode:2012Sci...336..455D. doi:10.1126/science.1212222. PMID 22539717. 
  18. ^Justin Gillis (April 26, 2012). "Study Indicates a Greater Threat of Extreme Weather". The New York Times. Retrieved April 27, 2012. 
  19. ^Vinas, Maria-Jose (2013-06-06). "NASA's Aquarius Sees Salty Shifts". NASA. Retrieved 2018-01-15. 
  20. ^"Retreat of Glaciers in Glacier National Park". Retrieved 2018-01-15. 
  21. ^"Water Cycle | Science Mission Directorate". Retrieved 2018-01-15. 
  22. ^"Rising sea levels attributed to global groundwater extraction". University of Utrecht. Retrieved February 8, 2011. 
  23. ^The Environmental Literacy Council. Biogeochemical Cycles. Retrieved on 2006-10-24.
  24. ^"Phosphorus Cycle - The Environmental Literacy Council". The Environmental Literacy Council. Retrieved 2018-01-15. 
  25. ^Ohio State University Extension Fact Sheet. Nitrogen and the Hydrologic Cycle. Retrieved on 2006-10-24.
  26. ^NASA's Earth Observatory. The Carbon Cycle. Retrieved on 2006-10-24.
  27. ^Nick Strobel (June 12, 2010). "Planetary Science". Archived from the original on September 28, 2010. Retrieved September 28, 2010. 
  28. ^Rudolf Dvořák (2007). Extrasolar Planets. Wiley-VCH. pp. 139–140. ISBN 978-3-527-40671-5. Retrieved 2009-05-05. 
  29. ^ abMorris, Henry M. (1988). Science and the Bible (Trinity Broadcasting Network Edition, 1988 ed.). Chicago, IL: Moody Press. p. 15.
  30. ^Metzger, Bruce M.; Coogan, Michael D. (1993). The Oxford Companion to the Bible. New York, NY: Oxford University Press. p. 369. ISBN 0195046455.
  31. ^Merrill, Eugene H.; Rooker, Mark F.; Grisanti, Michael A. (2011). The World and the Word. Nashville, TN: B&H Academic. p. 430. ISBN 9780805440317.
  32. ^Kazlev, M.Alan. "Palaeos: History of Evolution and Paleontology in science, philosophy, religion, and popular culture : Pre 19th Century". 
  33. ^ (page 9-10)
  34. ^Science?, Symposium on the Basis of Civilization--Water (1 January 2004). "The Basis of Civilization--water Science?". International Association of Hydrological Science – via Google Books. 
  35. ^Metzger, Bruce M.; Coogan, Michael D. (1993). The Oxford Companion to the Bible. New York, NY: Oxford University Press. p. 369. ISBN 0195046455. 
  36. ^Morris, Henry M. (1988). Science and the Bible (Trinity Broadcasting Network Edition, 1988 ed.). Chicago, IL: Moody Press. p. 15. 
  37. ^

Further reading

External links

Diagram of the Water Cycle
As the Earth's surface water evaporates, wind moves water in the air from the sea to the land, increasing the amount of freshwater on land.
Water vapor is converted to clouds that bring fresh water to land in the form of rain snow and sleet
Precipitation falls on the ground, but what happens to that water depends greatly on the geography of the land at any particular place.
Many different processes lead to movements and phase changes in water
Time-mean precipitation and evaporation as a function of latitude as simulated by an aqua-planet version of an atmospheric GCM (GFDL’s AM2.1) with a homogeneous “slab-ocean” lower boundary (saturated surface with small heat capacity), forced by annual mean insolation.
Global map of annual mean evaporation minus precipitation by latitude-longitude