what percent of water in the us returns to the atmosphere state with smallest amount of water

The Water Cycle

Design by Robert Simmon October 1, 2010

Viewed from space, one of the almost striking features of our home planet is the water, in both liquid and frozen forms, that covers approximately 75% of the Globe's surface. Geologic evidence suggests that large amounts of water have likely flowed on Earth for the by three.8 billion years—almost of its existence. Believed to have initially arrived on the surface through the emissions of ancient volcanoes, water is a vital substance that sets the Earth apart from the balance of the planets in our solar system. In particular, water appears to be a necessary ingredient for the development and nourishment of life.

World is a h2o planet: 3-quarters of the surface is covered past water, and water-rich clouds fill the sky. (NASA.)

Water, H2o, Everywhere

Water is practically everywhere on World. Moreover, it is the only known substance that can naturally exist as a gas, a liquid, and solid within the relatively small range of air temperatures and pressures found at the Earth'south surface.

Water is the only common substance that tin can exist naturally as a gas, liquid, or solid at the relatively small range of temperatures and pressures found on the Globe'south surface. Sometimes, all three states are even nowadays in the same time and place, such as this wintertime eruption of a geyser in Yellowstone National Park. (Photo ©2008 haglundc.)

In all, the Earth's h2o content is about one.39 billion cubic kilometers (331 million cubic miles), with the bulk of it, about 96.5%, being in the global oceans. As for the remainder, approximately 1.vii% is stored in the polar icecaps, glaciers, and permanent snow, and another i.7% is stored in groundwater, lakes, rivers, streams, and soil. Just a thousandth of 1% of the water on Earth exists equally water vapor in the temper.

Despite its small amount, this water vapor has a huge influence on the planet. H2o vapor is a powerful greenhouse gas, and it is a major driver of the Earth's conditions and climate equally it travels around the earth, transporting latent heat with it. Latent heat is heat obtained past water molecules as they transition from liquid or solid to vapor; the heat is released when the molecules condense from vapor dorsum to liquid or solid form, creating cloud droplets and various forms of atmospheric precipitation.

Water vapor—and with it free energy—is carried around the globe by weather systems. This satellite paradigm shows the distribution of h2o vapor over Africa and the Atlantic Sea. White areas have high concentrations of water vapor, while night regions are relatively dry out. The brightest white areas are towering thunderclouds. The prototype was acquired on the morning of September two, 2010 by SEVIRI aboard METEOSAT-9. [Watch this animation (23 MB QuickTime) of similar data to see the motion of water vapor over fourth dimension.] (Image ©2010 EUMETSAT.)

Estimate of Global Water Distribution	Volume (1000 km3)	Percent of Total Water	Percentage of Fresh Water
Oceans, Seas, and Bays	1,338,000	96.five	-
Ice Caps, Glaciers, and Permanent Snow	24,064	1.74	68.7
Groundwater	23,400	one.7	-
Fresh	(10,530)	(0.76)	30.1
Saline	(12,870)	(0.94)	-
Soil Wet	16.v	0.001	0.05
Ground Water ice and Permafrost	300	0.022	0.86
Lakes	176.4	0.013	-
Fresh	(91.0)	(0.007)	.26
Saline	(85.iv)	(0.006)	-
Atmosphere	12.nine	0.001	0.04
Swamp H2o	11.47	0.0008	0.03
Rivers	2.12	0.0002	0.006
Biological Water	1.12	0.0001	0.003
Total	1,385,984	100.0	100.0
Source: Gleick, P. H., 1996: Water resources. In Encyclopedia of Climate and Atmospheric condition, ed. by S. H. Schneider, Oxford University Press, New York, vol. two, pp.817-823.

For human needs, the amount of freshwater on Earth—for drinking and agriculture—is particularly important. Freshwater exists in lakes, rivers, groundwater, and frozen as snowfall and ice. Estimates of groundwater are especially hard to make, and they vary widely. (The value in the above table is nigh the high end of the range.)

Groundwater may constitute anywhere from approximately 22 to 30% of fresh h2o, with ice (including ice caps, glaciers, permanent snowfall, basis ice, and permafrost) accounting for most of the remaining 78 to lxx%.

A Multi-Phased Journey

The water, or hydrologic, cycle describes the pilgrimage of water as water molecules brand their way from the Earth's surface to the atmosphere and back once more, in some cases to below the surface. This gigantic organization, powered by energy from the Sun, is a continuous commutation of moisture between the oceans, the atmosphere, and the country.

Earth'due south water continuously moves through the atmosphere, into and out of the oceans, over the country surface, and underground. (Image courtesy NOAA National Weather condition Service Jetstream.)

Studies accept revealed that evaporation—the process by which water changes from a liquid to a gas—from oceans, seas, and other bodies of h2o (lakes, rivers, streams) provides nearly ninety% of the moisture in our atmosphere. Most of the remaining 10% found in the temper is released by plants through transpiration. Plants take in water through their roots, then release it through small pores on the underside of their leaves. In improver, a very small portion of water vapor enters the temper through sublimation, the procedure by which water changes directly from a solid (ice or snowfall) to a gas. The gradual shrinking of snow banks in cases when the temperature remains beneath freezing results from sublimation.

Together, evaporation, transpiration, and sublimation, plus volcanic emissions, account for almost all the water vapor in the atmosphere that isn't inserted through human being activities. While evaporation from the oceans is the main vehicle for driving the surface-to-temper portion of the hydrologic cycle, transpiration is also significant. For example, a cornfield ane acre in size can transpire every bit much as 4,000 gallons of water every day.

After the water enters the lower atmosphere, rise air currents deport it up, often loftier into the atmosphere, where the air is libation. In the absurd air, water vapor is more probable to condense from a gas to a liquid to form cloud droplets. Cloud droplets can abound and produce atmospheric precipitation (including pelting, snow, sleet, freezing rain, and hail), which is the primary machinery for transporting water from the atmosphere back to the Earth's surface.

When precipitation falls over the land surface, it follows diverse routes in its subsequent paths. Some of it evaporates, returning to the atmosphere; some seeps into the footing as soil moisture or groundwater; and some runs off into rivers and streams. Almost all of the water eventually flows into the oceans or other bodies of water, where the cycle continues. At different stages of the bicycle, some of the water is intercepted past humans or other life forms for drinking, washing, irrigating, and a large diversity of other uses.

Groundwater is found in two broadly divers layers of the soil, the "zone of aeration," where gaps in the soil are filled with both air and water, and, further down, the "zone of saturation," where the gaps are completely filled with water. The boundary between these two zones is known as the water tabular array, which rises or falls as the amount of groundwater changes.

The corporeality of water in the atmosphere at any moment in time is only 12,900 cubic kilometers, a infinitesimal fraction of Earth's full water supply: if it were to completely rain out, atmospheric moisture would cover the Earth'south surface to a depth of only ii.5 centimeters. Still, far more than h2o—in fact, some 495,000 cubic kilometers of it—are cycled through the atmosphere every year. It is as if the entire amount of water in the air were removed and replenished almost 40 times a year.

This map shows the distribution of water vapor throughout the depth of the temper during Baronial 2010. Even the wettest regions would form a layer of h2o merely 60 millimeters deep if it were condensed at the surface. (NASA paradigm by Robert Simmon, using AIRS & AMSU data.)

Water continually evaporates, condenses, and precipitates, and on a global basis, evaporation approximately equals precipitation. Because of this equality, the total amount of water vapor in the atmosphere remains approximately the same over fourth dimension. Nonetheless, over the continents, atmospheric precipitation routinely exceeds evaporation, and conversely, over the oceans, evaporation exceeds atmospheric precipitation.

In the case of the oceans, the continual excess of evaporation versus atmospheric precipitation would somewhen go out the oceans empty if they were not being replenished past additional means. Not only are they being replenished, largely through runoff from the land areas, but over the past 100 years, they have been over-replenished: bounding main level around the globe has risen approximately 17 centimeters over the grade of the twentieth century.

Ocean level has risen both because of warming of the oceans, causing water to expand and increase in volume, and because more water has been entering the ocean than the corporeality leaving information technology through evaporation or other means. A primary crusade for increased mass of water inbound the ocean is the calving or melting of land ice (water ice sheets and glaciers). Sea water ice is already in the ocean, so increases or decreases in the annual corporeality of sea water ice do not significantly affect bounding main level.

Blackfoot (left) and Jackson (right) glaciers, both in the mountains of Glacier National Park, were joined forth their margins in 1914, but have since retreated into split up alpine cirques. The melting of glacial ice is a major contributor to sea level rising. [Photographs by Eastward. B. Stebinger, Glacier National Park archives (1911), and Lisa McKeon, USGS (2009).]

Throughout the hydrologic cycle, there are many paths that a water molecule might follow. Water at the bottom of Lake Superior may eventually ascent into the atmosphere and autumn equally rain in Massachusetts. Runoff from the Massachusetts rain may drain into the Atlantic Bounding main and circulate northeastward toward Republic of iceland, destined to get role of a floe of bounding main water ice, or, afterward evaporation to the atmosphere and atmospheric precipitation as snow, role of a glacier.

H2o molecules can have an immense diverseness of routes and branching trails that lead them again and again through the iii phases of water ice, liquid h2o, and water vapor. For instance, the water molecules that in one case savage 100 years ago as rain on your great- grandparents' farmhouse in Iowa might now be falling as snow on your driveway in California.

The Water Cycle and Climatic change

Amidst the most serious Earth science and environmental policy bug against society are the potential changes in the Earth'southward water wheel due to climate change. The science community now generally agrees that the Globe'south climate is undergoing changes in response to natural variability, including solar variability, and increasing concentrations of greenhouse gases and aerosols. Furthermore, agreement is widespread that these changes may greatly affect atmospheric water vapor concentrations, clouds, precipitation patterns, and runoff and stream flow patterns.

Global climate change will affect the water wheel, likely creating perennial droughts in some areas and frequent floods in others. (Photograph ©2008 Garry Schlatter.)

For example, as the lower temper becomes warmer, evaporation rates will increase, resulting in an increase in the corporeality of wet circulating throughout the troposphere (lower atmosphere). An observed issue of higher water vapor concentrations is the increased frequency of intense atmospheric precipitation events, mainly over land areas. Furthermore, considering of warmer temperatures, more precipitation is falling equally rain rather than snow.

One expected effect of climatic change volition be an increase in precipitation intensity: a larger proportion of rain will autumn in a shorter amount of time than it has historically. Blue represents areas where climate models predict an increase in intensity past the end of the 21st century, brown represents a predicted decrease. (Map adjusted from the IPCC Fourth Cess Study.)

In parts of the Northern Hemisphere, an earlier inflow of spring-like conditions is leading to before peaks in snowmelt and resulting river flows. As a outcome, seasons with the highest water demand, typically summer and autumn, are being impacted by a reduced availability of fresh water.

Changes in water runoff into rivers and streams are another expected issue of climate change past the belatedly 21st Century. This map shows predicted increases in runoff in blue, and decreases in brown and cerise. (Map by Robert Simmon, using data from Chris Milly, NOAA Geophysical Fluid Dynamics Laboratory.)

Warmer temperatures have led to increased drying of the land surface in some areas, with the event of an increased incidence and severity of drought. The Palmer Drought Severity Index, which is a mensurate of soil moisture using precipitation measurements and crude estimates of changes in evaporation, has shown that from 1900 to 2002, the Sahel region of Africa has been experiencing harsher drought weather condition. This same index also indicates an contrary tendency in southern Southward America and the southward primal U.s..

Shifts in the water cycle occurred over the by century due to a combination of natural variations and man forcings. From 1900 to 2002, droughts worsened in Sub-Saharan and southern Africa, eastern Brazil, and Iran (chocolate-brown). Over the aforementioned period western Russia, due south-eastern S America, Scandinavia, and the southern Us had less severe droughts (green). (Map adapted from the IPCC Fourth Cess Report.)

While the brief scenarios described above stand for a small portion of the observed changes in the water bike, it should be noted that many uncertainties remain in the prediction of future climate. These uncertainties derive from the sheer complexity of the climate system, bereft and incomplete data sets, and inconsistent results given by current climate models. Withal, state of the fine art (but notwithstanding incomplete and imperfect) climate models do consistently predict that precipitation will become more variable, with increased risks of drought and floods at different times and places.

Observing the H2o Bike

Orbiting satellites are now collecting data relevant to all aspects of the hydrologic cycle, including evaporation, transpiration, condensation, atmospheric precipitation, and runoff. NASA even has ane satellite, Aqua, named specifically for the information it is collecting most the many components of the water cycle.

Aqua launched on May 4, 2002, with half dozen Earth-observing instruments: the Atmospheric Infrared Sounder (Arrogance), the Advanced Microwave Sounding Unit (AMSU), the Humidity Sounder for Brazil (HSB), the Avant-garde Microwave Scanning Radiometer for the Earth Observing System (AMSR-E), the Moderate Resolution Imaging Spectroradiometer (MODIS), and Clouds and the Earth'due south Radiant Free energy System (CERES).

NASA'southward Aqua satellite carries a suite of instruments designed primarily to study the water cycle. (NASA image past Marit Jentoft-Nilsen.)

Since water vapor is the Earth's main greenhouse gas, and it contributes significantly to uncertainties in projections of time to come global warming, information technology is disquisitional to understand how it varies in the World organization. In the first years of the Aqua mission, Arrogance, AMSU, and HSB provided space-based measurements of atmospheric temperature and water vapor that were more authentic than any obtained earlier; the sensors also fabricated measurements from more altitudes than whatsoever previous sensor. The HSB is no longer operational, but the AIRS/AMSU system continues to provide high-quality atmospheric temperature and h2o vapor measurements.

Aqua's Airs and AMSU instruments measure relative humidity at multiple pressure level levels, which correspond to distance. Near the surface (100 kPa), the air in a higher place the sea is almost saturated with water, while it is dry above Australia. It is by and large drier higher in the atmosphere (60 kPa), except where convection lifts moisture aloft. At the lower edge of the stratosphere (ten kPa) the air is almost universally dry. (NASA maps past Robert Simmon, based on Arrogance/AMSU data.)

More contempo studies using AIRS information have demonstrated that about of the warming caused by carbon dioxide does not come directly from carbon dioxide, but rather from increased water vapor and other factors that amplify the initial warming. Other studies accept shown improved estimation of the landfall of a hurricane in the Bay of Bengal by incorporating Arrogance temperature measurements, and improved understanding of large-scale atmospheric patterns such as the Madden-Julian Oscillation.

In addition to their importance to our weather, clouds play a major office in regulating Globe's climate arrangement. MODIS, CERES, and AIRS all collect data relevant to the study of clouds. The cloud data include the pinnacle and area of clouds, the liquid water they contain, and the sizes of deject aerosol and water ice particles. The size of deject particles affects how they reflect and absorb incoming sunlight, and the reflectivity (albedo) of clouds plays a major part in Globe's energy residual.

Loftier, thin cirrus clouds reflect relatively piddling sunlight dorsum into infinite compared to the amount reflected by thick cumulus clouds. This map shows the reflectivity of cirrus clouds [with a maximum of 30 percent (shown in white)] during March of 2010. (Map by Robert Simmon, using data from the MODIS Atmosphere Squad.)

One of the many variables AMSR-E monitors is global precipitation. The sensor measures microwave energy, some of which passes through clouds, and so the sensor tin can find the rainfall even under the clouds.

Water in the temper is hardly the only focus of the Aqua mission. Amongst much else, AMSR-E and MODIS are beingness used to report sea ice. Ocean water ice is important to the Earth organisation non just as an important element in the habitat of polar bears, penguins, and some species of seals, simply as well because information technology can insulate the underlying liquid h2o against heat loss to the often frigid overlying polar atmosphere and because information technology reflects sunlight that would otherwise exist available to warm the ocean.

When information technology comes to sea water ice, AMSR-E and MODIS provide complementary information. AMSR-Eastward doesn't record equally much item about ice features as MODIS does, just it tin can distinguish ice versus open water fifty-fifty when it is cloudy. The AMSR-E measurements go along, with improved resolution and accuracy, a satellite record of changes in the extent of polar ice that extends dorsum to the 1970s.

AMSR-Eastward and MODIS also provide monitoring of snow coverage over state, some other key indicator of climate modify. As with bounding main ice, AMSR-E allows routine monitoring of the snow, irrespective of cloud cover, only with less spatial particular, while MODIS sees greater spatial detail, but only nether cloud-free atmospheric condition.

Equally for liquid water on country, AMSR-E provides information virtually soil moisture, which is crucial for vegetation including agricultural crops. AMSR-E's monitoring of soil moisture globally permits, for example, the early identification of signs of drought.

More Water Cycle Observations

Aqua is the nearly comprehensive of NASA's water bike missions, simply information technology isn't alone. In fact, the Terra satellite also has MODIS and CERES instruments onboard, and several other spacecraft have made or are making unique water-bike measurements.

The Ice, Cloud, and State Elevation Satellite (ICESat) was launched in January 2003, and it collected information on the topography of the Earth'due south ice sheets, clouds, vegetation, and the thickness of sea water ice off and on until October 2009. A new ICESat mission, ICESat-2, is now under development and is scheduled to launch in 2015.

ICESat'south precise ascertainment of the surface elevation of Arctic sea ice enabled measurement of ice thickness. These images show that bounding main ice thinned from autumn 2003 to fall 2008. Night blue areas are thin water ice, white areas are thick water ice, greyness regions are land, and light blue due south of the water ice pack represents open water. (NASA images by the NASA GSFC Scientific Visualization Studio, using ICESat data.)

The Gravity Recovery and Climate Experiment (GRACE) is a unique mission that consists of two spacecraft orbiting one backside the other; changes in the distance between the ii provide information nearly the gravity field on the Earth beneath. Because gravity depends on mass, some of the changes in gravity over time bespeak a shift in water from ane place on Earth to another. Through measurements of irresolute gravity fields, GRACE scientists are able to derive data about changes in the mass of ice sheets and glaciers and fifty-fifty changes in groundwater around the world.

These GRACE data show monthly gravity differences calculated from a 2003-2007 baseline. The big contrasts in the Amazon are due to seasonal changes in rainfall. (NASA maps by Robert Simmon, using GRACE information.)

CloudSat is advancing scientists' understanding of cloud abundance, distribution, structure, and radiative backdrop (how they absorb and emit energy, including thermal infrared energy escaping from Earth's surface). Since 2006, CloudSat has flown the first satellite-based, millimeter-wavelength cloud radar—an instrument that is g times more sensitive than existing weather radars on the basis. Unlike ground-based weather condition radars that apply centimeter wavelengths to detect raindrop-sized particles, CloudSat's radar allows the detection of the much smaller particles of liquid water and ice in the large cloud masses that contribute significantly to our weather.

CloudSat's radar measures the vertical distribution of clouds, such as this contour of Hurricane Julia. (NASA image past Jesse Allen, based on MODIS and CloudSat data.)

The joint NASA and French Deject-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) is providing new insight into the office that clouds and atmospheric aerosols (particles like dust and pollution) play in regulating Earth'south weather, climate, and air quality. CALIPSO combines an active laser instrument with passive infrared and visible imagers to probe the vertical structure and properties of sparse clouds and aerosols over the globe.

CloudSat (top) and CALIPSO (lower) are two satellites providing detailed views of the structure of clouds. (NASA images by Marit Jentoft-Nilsen.)

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Source: https://earthobservatory.nasa.gov/features/Water

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