Water cycle

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
Relationship between impervious surfaces and surface runoff
Diagram of the water cycle
Natural water cycle

Biogeochemical cycle that describes the continuous movement of water on, above and below the surface of the Earth.

- Water cycle

298 related topics


Surface runoff

Flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil.

Runoff flowing into a stormwater drain
Surface runoff from a hillside after soil is saturated
Precipitation washing contaminates into local streams
Urban surface water runoff
Willow hedge strengthened with fascines for the limitation of runoff, north of France.
Soil erosion by water on intensively-tilled farmland.
Farmland runoff
Runoff holding ponds (Uplands neighborhood of North Bend, Washington)

Surface runoff is a major component of the water cycle.


Body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water.

World map of the five-ocean model with approximate boundaries
The Atlantic, one component of the system, makes up 23% of the "global ocean".
Surface view of the Atlantic Ocean
World distribution of mid-oceanic ridges; USGS
Map of large underwater features (1995, NOAA)
Ocean chlorophyll concentration is a proxy for phytoplankton biomass. In this map, blue colors represent lower chlorophyll and reds represent higher chlorophyll. Satellite-measured chlorophyll is estimated based on ocean color by how green the color of the water appears from space.
The major oceanic zones, based on depth and biophysical conditions
Ocean surface currents
A map of the global thermohaline circulation; blue represents deep-water currents, whereas red represents surface currents.
Map of the Gulf Stream, a major ocean current that transports heat from the equator to northern latitudes and moderates the climate of Europe.
High tide and low tide in the Bay of Fundy, Canada.
The ocean is a major driver of Earth's water cycle.
Annual mean sea surface salinity in practical salinity units (psu) from the World Ocean Atlas.
Sea surface oxygen concentration in moles per cubic meter from the World Ocean Atlas.
Diagram of the ocean carbon cycle showing the relative size of stocks (storage) and fluxes.
Residence time of elements in the ocean depends on supply by processes like rock weathering and rivers vs. removal by processes like evaporation and sedimentation.

Acting as a huge heat reservoir, the ocean influences climate and weather patterns, the carbon cycle, and the water cycle.


Term used to refer to the combined processes by which water moves from the earth’s surface into the atmosphere.

Water cycle of the Earth's surface, showing the individual components of transpiration and evaporation that make up evapotranspiration. Other closely related processes shown are runoff and groundwater recharge.
Monthly estimated potential evapotranspiration and measured pan evaporation for two locations in Hawaii, Hilo and Pahala.
Classification of RS-based ET models based on sensible heat flux estimation approaches

Evapotranspiration is an important part of the local water cycle and climate, as well as measurement of it plays a key role in agricultural irrigation and water resource management.


Inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a solvent ).

A water molecule consists of two hydrogen atoms and one oxygen atom
The three common states of matter
Phase diagram of water (simplified)
Tetrahedral structure of water
Model of hydrogen bonds (1) between molecules of water
Water cycle
Overview of photosynthesis (green) and respiration (red)
Water fountain
An environmental science program – a student from Iowa State University sampling water
Total water withdrawals for agricultural, industrial and municipal purposes per capita, measured in cubic metres (m³) per year in 2010
A young girl drinking bottled water
Water availability: the fraction of the population using improved water sources by country
Roadside fresh water outlet from glacier, Nubra
Hazard symbol for non-potable water
Water is used for fighting wildfires.
San Andrés island, Colombia
Water can be used to cook foods such as noodles
Sterile water for injection
Band 5 ALMA receiver is an instrument specifically designed to detect water in the universe.
South polar ice cap of Mars during Martian south summer 2000
An estimate of the proportion of people in developing countries with access to potable water 1970–2000
People come to Inda Abba Hadera spring (Inda Sillasie, Ethiopia) to wash in holy water
Icosahedron as a part of Spinoza monument in Amsterdam.
Water requirement per tonne of food product
Irrigation of field crops
Specific heat capacity of water

Water moves continually through the water cycle of evaporation, transpiration (evapotranspiration), condensation, precipitation, and runoff, usually reaching the sea.


Any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds.

Mean precipitation based on global high resolution climate data (CHELSA)
Countries by average annual precipitation
A thunderstorm with heavy precipitation
Late-summer rainstorm in Denmark
Lenticular cloud forming due to mountains over Wyoming
Condensation and coalescence are important parts of the water cycle.
Puddle in the rain
An accumulation of ice pellets
A large hailstone, about 6 cm in diameter
Snowflake viewed in an optical microscope
Convective precipitation
Orographic precipitation
Lake-effect snow bands near the Korean Peninsula in early December 2008
Rainfall distribution by month in Cairns showing the extent of the wet season at that location
Standard rain gauge
Updated Köppen-Geiger climate map
Rainfall estimates for southern Japan and the surrounding region from July 20 to 27, 2009.
Extreme precipitation events have become more common in the U.S. over recent decades.
Image of Atlanta, Georgia, showing temperature distribution, with hot areas appearing white
Example of a five-day rainfall forecast from the Hydrometeorological Prediction Center

Precipitation is a major component of the water cycle, and is responsible for depositing fresh water on the planet.


Liquid water in the form of droplets that have condensed from atmospheric water vapor and then become heavy enough to fall under gravity.

Hard rain on a roof
Rain falling on a field, in southern Estonia
Streets in Tampere, Finland watered by night rain.
The shape of rain drops depending upon their size
Black Rain Clouds
A raindrop on a leaf
Convective precipitation
Orographic precipitation
Rainfall distribution by month in Cairns showing the extent of the wet season at that location
Image of Atlanta, US showing temperature distribution, with blue showing cool temperatures, red warm, and hot areas appearing white.
Average surface air temperatures from 2011 to 2020 compared to the 1951–1980 average. Source: NASA
Band of thunderstorms seen on a weather radar display
Sources of acid rain
Updated Köppen–Geiger climate map
Standard rain gauge
Twenty-four-hour rainfall accumulation on the Val d'Irène radar in Eastern Canada. Zones without data in the east and southwest are caused by beam blocking from mountains. (Source: Environment Canada)
Example of a five-day rainfall forecast from the Hydrometeorological Prediction Center
Rainfall estimates for southern Japan and the surrounding region from July 20–27, 2009.
A rain dance being performed in Harar, Ethiopia
Rain, depicted in the 1493 Nuremberg Chronicle
Largest deserts
Isolated towering vertical desert shower
Long-term mean precipitation by month

Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth.

Fresh water

Any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids.

Visualisation of the distribution (by volume) of water on Earth. Each tiny cube (such as the one representing biological water) corresponds to approximately 1400 cubic km of water, with a mass of approximately 1.4 trillion tonnes (235000 times that of the Great Pyramid of Giza or 8 times that of Lake Kariba, arguably the heaviest man-made object). The entire block comprises 1 million tiny cubes.
A graphical distribution of the locations of water on Earth. Only 3% of the Earth's water is fresh water. Most of it is in icecaps and glaciers (69%) and groundwater (30%), while all lakes, rivers and swamps combined only account for a small fraction (0.3%) of the Earth's total freshwater reserves.

Fresh water is replenished through the process of the water cycle, in which water from seas, lakes, forests, land, rivers and reservoirs evaporates, forms clouds, and returns inland as precipitation.


Surface runoff produced from melting snow.

Vegetation gives off heat, resulting in this circular snowmelt pattern.
2005 (Less dust)
2006 (More dust)
2008 (Less dust)
2009 (More dust)

Water produced by snowmelt is an important part of the annual water cycle in many parts of the world, in some cases contributing high fractions of the annual runoff in a watershed.

Groundwater recharge

Hydrologic process, where water moves downward from surface water to groundwater.

Water balance
Natural processes of groundwater recharge. Adjustments affecting the water table will drastically enhance or diminish the quality of groundwater recharge in a specific region.

Recharge occurs both naturally (through the water cycle) and through anthropogenic processes (i.e., "artificial groundwater recharge"), where rainwater and or reclaimed water is routed to the subsurface.


Aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space.

Stratocumuliform cloudscape
Tropospheric cloud classification by altitude of occurrence: Multi-level and vertical genus-types not limited to a single altitude level include nimbostratus, cumulonimbus, and some of the larger cumulus species.
Cumulus humilis clouds in May
Windy evening twilight enhanced by the Sun's angle, can visually mimic a tornado resulting from orographic lift
Nimbostratus cloud producing precipitation
Cirrus fibratus clouds in March
Stratocumulus over Orange County.
Stratocumulus cloud
Cumulus humilis clouds
Cumulonimbus cloud over the Gulf of Mexico in Galveston, Texas
High cirrus upper-left merging into cirrostratus and some cirrocumulus upper right
A large field of cirrocumulus
Sunrise scene giving a shine to an altocumulus stratiformis perlucidus cloud (see also 'species and varieties')
Altostratus translucidus near top of photo merging into altostratus opacus near bottom
Cumulus humilis clouds over Jakarta, Indonesia
Stratocumulus stratiformis perlucidus over Galapagos, Tortuga Bay (see also 'species and varieties')
Stratus nebulosus translucidus
Deep multi-level nimbostratus cloud covering the sky with a scattered layer of low stratus fractus pannus (see also 'species' and 'supplementary features' sections)
Cumulus humilis and cumulus mediocris with stratocumulus stratiformis perlucidus in the foreground (see also 'species and varieties')
Towering vertical cumulus congestus embedded within a layer of cumulus mediocris: Higher layer of stratocumulus stratiformis perlucidus.
Progressive evolution of a single cell thunderstorm
Isolated cumulonimbus cloud over the Mojave Desert, releasing a heavy shower
Altocumulus lenticularis forming over mountains in Wyoming with lower layer of cumulus mediocris and higher layer of cirrus spissatus
Example of a castellanus cloud formation
Cumulus mediocris cloud, about to turn into a cumulus congestus
A layer of stratocumulus stratiformis perlucidus hiding the setting sun with a background layer of stratocumulus cumulogenitus resembling distant mountains.
Cirrus fibratus radiatus over ESO's La Silla Observatory
Altocumulus stratiformis duplicatus at sunrise in the California Mojave Desert, USA (higher layer orange to white; lower layer grey)
Cumulus partly spreading into stratocumulus cumulogenitus over the port of Piraeus in Greece
Cumulonimbus mother cloud dissipating into stratocumulus cumulonimbogenitus at dusk
Cirrus fibratus intortus formed into a Kármán vortex street at evening twilight
Global cloud cover, averaged over the month of October 2009. NASA composite satellite image.
Lenticular nacreous clouds over Antarctica
Noctilucent cloud over Estonia
Joshua Passing the River Jordan with the Ark of the Covenant (1800) by Benjamin West, showing Yahweh leading the Israelites through the desert in the form of a pillar of cloud, as described in
Stratocumulus stratiformis and small castellanus made orange by the sun rising
An occurrence of cloud iridescence with altocumulus volutus and cirrocumulus stratiformis
Sunset reflecting shades of pink onto grey stratocumulus stratiformis translucidus (becoming perlucidus in the background)
Stratocumulus stratiformis perlucidus before sunset. Bangalore, India.
Late-summer rainstorm in Denmark. Nearly black color of base indicates main cloud in foreground probably cumulonimbus.
Particles in the atmosphere and the sun's angle enhance colors of stratocumulus cumulogenitus at evening twilight

Nevertheless, it was the first known work that attempted to treat a broad range of meteorological topics in a systematic way, especially the hydrological cycle.