The water cycle, also known as the hydrologic cycle or the hydrological 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.
Contents
1 Description
1.1 Processes
2 Residence times
3 Changes over time
4 Effects on climate
5 Effects on biogeochemical cycling
6 Slow loss over geologic time
7 History of hydrologic cycle theory
7.1 Floating land mass
7.2 Hebrew Bible
7.3 Precipitation and percolation
7.4 Precipitation alone
8 See also
9 References
10 Further reading
11 External links
Description
The sun, which drives the water cycle, heats water in oceans and seas. Water evaporates as water vapor into the air. Some ice and snow 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 and oxygen, N
2 and O
2, 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 fall unless supported by an updraft. A huge concentration of these droplets over a large space up in the atmosphere become visible as cloud. Some condensation is near ground level, and called fog.
Atmospheric circulation moves water vapor 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.
Processes
Many different processes lead to movements and phase changes in water
Precipitation
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.
Snowmelt
The runoff produced by melting snow.
Runoff
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.
Infiltration
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.
Evaporation
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]
Sublimation
The state change directly from solid water (snow or ice) to water vapor by passing the liquid state.[8]
Deposition
This refers to changing of water vapor directly to ice.
Advection
The movement of water through the atmosphere.[9] Without advection, water that evaporated over the oceans could not precipitate over land.
Condensation
The transformation of water vapor to liquid water droplets in the air, creating clouds and fog.[10]
Transpiration
The release of water vapor from plants and soil into the air.
Percolation
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.
Residence times
Average reservoir residence times[11]
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. 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
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
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.[16][18]
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.[19]
Human activities that alter the water cycle include:
agriculture
industry
alteration of the chemical composition of the atmosphere
construction of dams
deforestation and afforestation
removal of groundwater from wells
water abstraction from rivers
urbanization
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.[20] 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.[21]
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.[22] Runoff is responsible for almost all of the transport of eroded sediment and phosphorus from land to waterbodies.[23] 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.[24] 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.[25]
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.[26] Planets with hot lower atmospheres could result in humid upper atmospheres that accelerate the loss of hydrogen.[27]
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).
Hebrew Bible
In the ancient near east, Hebrew scholars observed that even though the rivers ran into the sea, the sea never became full. 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" (, KJV).[28] Scholars are not in agreement as to the date of Ecclesiastes, though most scholars point to a date during the time of King Solomon, son of David and Bathsheba, "three thousand years ago,[28] there is some agreement that the time period is 962–922 BCE.[29] Furthermore, it was also observed that when the clouds were full, they emptied rain on the earth (). In addition, during 793–740 BCE a Hebrew prophet, Amos, stated that water comes from the sea and is poured out on the earth (, ).[30]
In the Biblical Book of Job, dated between 7th and 2nd centuries BCE,[29] there is a description of precipitation in the hydrologic cycle,[28] "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" (, KJV).
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[31]) and Xenophanes of Colophon (530 BCE).[32] Chinese scholars such as Chi Ni Tzu (320 BCE) and Lu Shih Ch'un Ch'iu (239 BCE) had similar thoughts.[33] 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
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.[34]
Water cycle
WRITTEN BY: The Editors of Encyclopaedia Britannica
LAST UPDATED: Feb 14, 2019 See Article History
Alternative Titles: hydrologic cycle, moisture cycle
Water cycle, also called hydrologic cycle, cycle that involves the continuous circulation of water in the Earth-atmosphere system. Of the many processes involved in the water cycle, the most important are evaporation, transpiration, condensation, precipitation, and runoff. Although the total amount of water within the cycle remains essentially constant, its distribution among the various processes is continually changing.
Earth's environmental spheres
READ MORE ON THIS TOPIC
hydrosphere
…is the concept of the water cycle (or hydrologic cycle). This cycle consists of a group of reservoirs containing water, the processes by…
A brief treatment of the water cycle follows. For full treatment, see hydrosphere: The water cycle.
Evaporation, one of the major processes in the cycle, is the transfer of water from the surface of the Earth to the atmosphere. By evaporation, water in the liquid state is transferred to the gaseous, or vapour, state. This transfer occurs when some molecules in a water mass have attained sufficient kinetic energy to eject themselves from the water surface. The main factors affecting evaporation are temperature, humidity, wind speed, and solar radiation. The direct measurement of evaporation, though desirable, is difficult and possible only at point locations. The principal source of water vapour is the oceans, but evaporation also occurs in soils, snow, and ice. Evaporation from snow and ice, the direct conversion from solid to vapour, is known as sublimation. Transpiration is the evaporation of water through minute pores, or stomata, in the leaves of plants. For practical purposes, transpiration and the evaporation from all water, soils, snow, ice, vegetation, and other surfaces are lumped together and called evapotranspiration, or total evaporation.
water cycle
water cycle
The water cycle begins and ends in the ocean.
Created and produced by QA International. © QA International, 2010. All rights reserved. www.qa-international.com
Water vapour is the primary form of atmospheric moisture. Although its storage in the atmosphere is comparatively small, water vapour is extremely important in forming the moisture supply for dew, frost, fog, clouds, and precipitation. Practically all water vapour in the atmosphere is confined to the troposphere (the region below 6 to 8 miles [10 to 13 km] altitude).
hydrologic cycle
hydrologic cycle
An overview of how water in its various phases flows through the hydrologic, or water, cycle.
Encyclopædia Britannica, Inc.
The transition process from the vapour state to the liquid state is called condensation. Condensation may take place as soon as the air contains more water vapour than it can receive from a free water surface through evaporation at the prevailing temperature. This condition occurs as the consequence of either cooling or the mixing of air masses of different temperatures. By condensation, water vapour in the atmosphere is released to form precipitation.
Precipitation that falls to the Earth is distributed in four main ways: some is returned to the atmosphere by evaporation, some may be intercepted by vegetation and then evaporated from the surface of leaves, some percolates into the soil by infiltration, and the remainder flows directly as surface runoff into the sea. Some of the infiltrated precipitation may later percolate into streams as groundwater runoff. Direct measurement of runoff is made by stream gauges and plotted against time on hydrographs.
Most groundwater is derived from precipitation that has percolated through the soil. Groundwater flow rates, compared with those of surface water, are very slow and variable, ranging from a few millimetres to a few metres a day. Groundwater movement is studied by tracer techniques and remote sensing.
Ice also plays a role in the water cycle. Ice and snow on the Earth’s surface occur in various forms such as frost, sea ice, and glacier ice. When soil moisture freezes, ice also occurs beneath the Earth’s surface, forming permafrost in tundra climates. About 18,000 years ago glaciers and ice caps covered approximately one-third of the Earth’s land surface. Today about 12 percent of the land surface remains covered by ice masses.
Hydrologic Cycle10.08.03
A bucket with a hole in the bottom illustrates how water recycles on earth by dripping in the top and out the bottom Many processes work together to keep Earth's water moving in a cycle. There are five processes at work in the hydrologic cycle: condensation, precipitation, infiltration, runoff, and evapotranspiration. These occur simultaneously and, except for precipitation, continuously.
Together, these five processes - condensation, precipitation, infiltration, runoff, and evapotranspiration- make up the Hydrologic Cycle. Water vapor condenses to form clouds, which result in precipitation when the conditions are suitable. Precipitation falls to the surface and infiltrates the soil or flows to the ocean as runoff. Surface water (e.g., lakes, streams, oceans, etc.), evaporates, returning moisture to the atmosphere, while plants return water to the atmosphere by transpiration.
Condensation is the process of water changing from a vapor to a liquid. Water vapor in the air rises mostly by convection. This means that warm, humid air will rise, while cooler air will flow downward. As the warmer air rises, the water vapor will lose energy, causing its temperature to drop. The water vapor then has a change of state into liquid or ice.
Warm air rises, cool air condenses into clouds
Warm air rises, cool air condenses into clouds
You can see condensation in action whenever you take a cold soda from the refrigerator and set it in a room. Notice how the outside of the soda can "sweats?" The water doesn't come from inside the can, it comes from the water vapor in the air. As the air cools around the can water droplets form.
Precipitation is water being released from clouds as rain, sleet, snow, or hail. Precipitation begins after water vapor, which has condensed in the atmosphere, becomes too heavy to remain in atmospheric air currents and falls.
Under some circumstances precipitation actually evaporates before it reaches the surface. More often, though, precipitation reaches the Earth's surface, adding to the surface water in streams and lakes, or infiltrating the soil to become groundwater.
A portion of the precipitation that reaches the Earth's surface seeps into the ground through the process called infiltration. The amount of water that infiltrates the soil varies with the degree of land slope, the amount and type of vegetation, soil type and rock type, and whether the soil is already saturated by water. The more openings in the surface (cracks, pores, joints), the more infiltration occurs. Water that doesn't infiltrate the soil flows on the surface as runoff.
A portion of the precipitation that reaches the Earth's surface seeps into the ground through the process called infiltration
A portion of the precipitation that reaches the Earth's surface seeps into the ground through the process called infiltration
Precipitation that reaches the surface of the Earth but does not infiltrate the soil is called runoff. Runoff can also come from melted snow and ice.
When there is a lot of precipitation, soils become saturated with water. Additional rainfall can no longer enter it. Runoff will eventually drain into creeks, streams, and rivers, adding a large amount of water to the flow. Surface water always travels towards the lowest point possible, usually the oceans. Along the way some water evaporates, percolates into the ground, or is used for agricultural, residential, or industrial purposes.
Evapotranspiration is water evaporating from the ground and transpiration by plants. Evapotranspiration is also the way water vapor re-enters the atmosphere.
Evaporation occurs when radiant energy from the sun heats water, causing the water molecules to become so active that some of them rise into the atmosphere as vapor.
Transpiration occurs when plants take in water through the roots and release it through the leaves, a process that can clean water by removing contaminants and pollution.
As you can see, many process are at work to give you the water you need. And these processes are always at work. Just because Antarctica is frozen doesn't mean that evaporation is not taking place (ice can turn directly to water vapor by a process called sublimation). And because the Sahara Desert is so dry doesn't mean that precipitation is not happening (it evaporates before it makes it to the ground).
Water Cycle The funny thing is that the water that falls from the sky as rain today, might have fallen last week, last month, last year or thousands of years ago. It is the greatest recycler of all time!
There are four main stages in the water cycle. They are evaporation, condensation, precipitation and collection. Let's look at each of these stages.
Evaporation: This is when warmth from the sun causes water from oceans, lakes, streams, ice and soils to rise into the air and turn into water vapour (gas). Water vapour droplets join together to make clouds!
Condensation: This is when water vapour in the air cools down and turns back into liquid water.
Precipitation: This is when water (in the form of rain, snow, hail or sleet) falls from clouds in the sky.
Collection: This is when water that falls from the clouds as rain, snow, hail or sleet, collects in the oceans, rivers, lakes, streams. Most will infiltrate (soak into) the ground and will collect as underground water.
The water cycle is powered by the sun's energy and by gravity. The sun kickstarts the whole cycle by heating all the Earth's water and making it evaporate. Gravity makes the moisture fall back to Earth.
About Water Water is found pretty much everywhere on planet Earth, including the atmosphere and the frozen polar icecaps.
Most water on the planet is salty and is not good to drink. We are lucky in Ireland that we have plenty of freshwater. The problem is that we don't always look after it.
The salty water is found in vast oceans like the Atlantic Ocean. There are five oceans in all: The Pacific Ocean, Atlantic Ocean, Indian Ocean, Antarctic Ocean and Arctic Ocean. There are also seas, like the Irish Sea. These are full of water that is not good to drink because it is too salty!
Freshwater is found in rivers, lakes and streams. We have many of these in Ireland! All lakes, rivers and streams have freshwater that might be good to drink, but only if that water is clean and has been properly treated.
There are also vast amounts of water underground that we cannot see, except when they come to the surface as spring wells, rivers or turloughs. A turlough is a 'disappearing lake' found in areas covered in a special type of rock called limestone. When the level of the underground water is high, these lakes become flooded. They then dry up again when the underground water level drops. In some countries underground water bursts out of the ground as 'geysers'!
Conservation What can you do to help conserve water? Plenty!
1. Check for leaks and have them fixed!!
2. No power showers and no baths (unless it is shared with your brothers and sisters) ... ordinary showers only, turning it off while soaping your body and washing your hair. And be quick about it!
3. No leaving the tap on while brushing teeth or washing your face ... wet the brush/face cloth, then turn off the tap until rinsing.
4. Don't flush as much ... if it's yellow, let it mellow, if it's brown flush it down! ... and use a plastic litre bottle or a 'Happy Hippo' in the toilet cistern to reduce the amount of water used in each flush.
5. Don't leave taps running in the kitchen either. Use a basin or bowl to wash the dishes or fill up the dishwasher (if it's modern).
6. Also use a basin for washing vegetables and when cleaning about the house.
7. Make sure the washing machine/dishwater has a full load.
8. Keep a jug of water in the fridge, so that you don't have to run the tap to have a cold drink.
9. In the garden, the use of hoses and water features that demand fresh water are banned ... use wastewater from washing dishes/ vegetables and even from showers etc. This is the only water that should be used in the garden during a drought, unless your family has been smart enough to catch rainwater in a barrel or water butt.
10: Don't cut lawns too short. By leaving the grass a little longer, morning dew is trapped and evaporation is reduced. Using mulch also reduces evaporation and lowers water demand.
11. Use watering cans, but only during the coolest part of the day.
12. If the car has to be washed, then use a bucket filled with the wastewater from your sink or shower.
Pollution How can you help prevent water pollution?
Precipitation is a vital component of how water moves through Earth’s water cycle, connecting the ocean, land, and atmosphere. Knowing where it rains, how much it rains and the character of the falling rain, snow or hail allows scientists to better understand precipitation’s impact on streams, rivers, surface runoff and groundwater. Frequent and detailed measurements help scientists make models of and determine changes in Earth’s water cycle.
The water cycle describes how water evaporates from the surface of the earth, rises into the atmosphere, cools and condenses into rain or snow in clouds, and falls again to the surface as precipitation. The water falling on land collects in rivers and lakes, soil, and porous layers of rock, and much of it flows back into the oceans, where it will once more evaporate. The cycling of water in and out of the atmosphere is a significant aspect of the weather patterns on Earth.
1. Never flush anything down the toilet that isn't suppose to be flushed.
2. Pick up pet poo - it's the law! Never leave pet poo on the footpath or ground where it might wash into gutters and down storm drains. Use doggy bags to put it in the bin.
3. Start building a compost heap and encourage your parents to use it. You can compost everything from food peelings, to teabags, paper, grass and even wooly jumpers.
4. Don't wash your parents' car in the driveway. If you do, harmful chemicals might end up in the drains and flow into rivers and lakes. Ask your parents to drive it onto the lawn or onto a gravel drive. That way the soapy water will soak into the ground and the soil will help filter out the pollutants!
5. If you see your parents' car leaking oil, ask them to get it fixed!
6. Throw your rubbish into the bin, not onto the street.
7. Reduce, reuse and recycle waste whenever you can!
Summary:
Water is a vital substance that sets the Earth apart from the rest of the planets in our solar system. In particular, water appears to be a necessary ingredient for the development and nourishment of life.
Viewed from space, one of the most striking features of our home planet is the water, in both liquid and frozen forms, that covers approximately 75% of the Earth’s surface. Geologic evidence suggests that large amounts of water have likely flowed on Earth for the past 3.8 billion years—most 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 rest of the planets in our solar system. In particular, water appears to be a necessary ingredient for the development and nourishment of life.
Earth is a water planet: three-quarters of the surface is covered by water, and water-rich clouds fill the sky. (NASA.)
Water, Water, Everywhere
Water is practically everywhere on Earth. 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’s surface.
Water is the only common substance that can exist naturally as a gas, liquid, or solid at the relatively small range of temperatures and pressures found on the Earth’s surface. Sometimes, all three states are even present in the same time and place, such as this wintertime eruption of a geyser in Yellowstone National Park. (Photograph ©2008 haglundc.)
In all, the Earth’s water content is about 1.39 billion cubic kilometers (331 million cubic miles), with the bulk of it, about 96.5%, being in the global oceans. As for the rest, approximately 1.7% is stored in the polar icecaps, glaciers, and permanent snow, and another 1.7% is stored in groundwater, lakes, rivers, streams, and soil. Only a thousandth of 1% of the water on Earth exists as water vapor in the atmosphere.
Despite its small amount, this water vapor has a huge influence on the planet. Water vapor is a powerful greenhouse gas, and it is a major driver of the Earth’s weather and climate as it travels around the globe, transporting latent heat with it. Latent heat is heat obtained by water molecules as they transition from liquid or solid to vapor; the heat is released when the molecules condense from vapor back to liquid or solid form, creating cloud droplets and various forms of precipitation.
Water vapor—and with it energy—is carried around the globe by weather systems. This satellite image shows the distribution of water vapor over Africa and the Atlantic Ocean. White areas have high concentrations of water vapor, while dark regions are relatively dry. The brightest white areas are towering thunderclouds. The image was acquired on the morning of September 2, 2010 by SEVIRI aboard METEOSAT-9. [Watch this animation (23 MB QuickTime) of similar data to see the movement of water vapor over time.] (Image ©2010 EUMETSAT.)| Estimate of Global Water Distribution | Volume (1000 km3) | Percent of Total Water | Percent of Fresh Water |
|---|---|---|---|
| Oceans, Seas, and Bays | 1,338,000 | 96.5 | - |
| Ice Caps, Glaciers, and Permanent Snow | 24,064 | 1.74 | 68.7 |
| Groundwater | 23,400 | 1.7 | - |
| Fresh | (10,530) | (0.76) | 30.1 |
| Saline | (12,870) | (0.94) | - |
| Soil Moisture | 16.5 | 0.001 | 0.05 |
| Ground Ice and Permafrost | 300 | 0.022 | 0.86 |
| Lakes | 176.4 | 0.013 | - |
| Fresh | (91.0) | (0.007) | .26 |
| Saline | (85.4) | (0.006) | - |
| Atmosphere | 12.9 | 0.001 | 0.04 |
| Swamp Water | 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 Weather, ed. by S. H. Schneider, Oxford University Press, New York, vol. 2, 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 snow and ice. Estimates of groundwater are particularly difficult to make, and they vary widely. (The value in the above table is near the high end of the range.)
Groundwater may constitute anywhere from approximately 22 to 30% of fresh water, with ice (including ice caps, glaciers, permanent snow, ground ice, and permafrost) accounting for most of the remaining 78 to 70%.
NASA Earth Science: Water Cycle
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This article explains the basics behind the water cycle and includes many good visuals. It provides some good background information about our water cycle as well as providing students with many real-world applications.
Earth is a truly unique in its abundance of water. Water is necessary to sustaining life on Earth, and helps tie together the Earth's lands, oceans, and atmosphere into an integrated system. Precipitation, evaporation, freezing and melting and condensation are all part of the hydrological cycle - a never-ending global process of water circulation from clouds to land, to the ocean, and back to the clouds. This cycling of water is intimately linked with energy exchanges among the atmosphere, ocean, and land that determine the Earth's climate and cause much of natural climate variability. The impacts of climate change and variability on the quality of human life occur primarily through changes in the water cycle. As stated in the National Research Council's report on Research Pathways for the Next Decade (NRC, 1999): "Water is at the heart of both the causes and effects of climate change."
Importance of the ocean in the water cycle
The ocean plays a key role in this vital cycle of water. 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. Besides affecting the amount of atmospheric water vapor and hence rainfall, evaporation from the sea surface is important in the movement of heat in the climate system. Water evaporates from the surface of the ocean, mostly in warm, cloud-free subtropical seas. This cools the surface of the ocean, and the large amount of heat absorbed the ocean partially buffers the greenhouse effect from increasing carbon dioxide and other gases. Water vapor carried by the atmosphere condenses as clouds and falls as rain, mostly in the ITCZ, far from where it evaporated, Condensing water vapor releases latent heat and this drives much of the the atmospheric circulation in the tropics. This latent heat release is an important part of the Earth’s heat balance, and it couples the planet’s energy and water cycles.
The major physical components of the global water cycle include the evaporation from the ocean and land surfaces, the transport of water vapor by the atmosphere, precipitation onto the ocean and land surfaces, the net atmospheric transport of water from land areas to ocean, and the return flow of fresh water from the land back into the ocean. The additional components of oceanic water transport are few, including the mixing of fresh water through the oceanic boundary layer, transport by ocean currents, and sea ice processes. On land the situation is considerably more complex, and includes the deposition of rain and snow on land; water flow in runoff; infiltration of water into the soil and groundwater; storage of water in soil, lakes and streams, and groundwater; polar and glacial ice; and use of water in vegetation and human activities. Illustration of the water cycle showing the ocean, land, mountains, and rivers returning to the ocean. Processes labeled include: precipitation, condensation, evaporation, evaportranspiration (from tree into atmosphere), radiative exchange, surface runoff, ground water and stream flow, infiltration, percolation and soil moisture.
The hydrologic cycle describes the pilgrimage of water as water molecules make their way from the Earth's surface to the atmosphere, and back again. This gigantic system, powered by energy from the sun, is a continuous exchange of moisture between the oceans, the atmosphere, and the land. Credit: NASA GSFC Water and Energy Cycle web site. This diagram show the relationship between Physical Oceanography, Biological Oceanography, and Water Cycle. Feedbacks between Physical Oceanography and Water Cycle are Evaporation minus Precipitation and Fresh water transports (i.e. Goldsborough Circulation). Biological in the ocean is affected by the water cycle via the Mixed Layer Depth and Run off from land. Finally, feedback between Physical and Biological Oceanography include the sea-ice and haline enivironments.
Evaporation ("E") controls the loss of fresh water and precipitation ("P") governs most of the gain of fresh water. Scientists monitor the relationship between these two primary processes in the oceans. Inputs from rivers and melting ice can also contribute to fresh water gains. Evaporation minus precipitation is usually referred to as the net flux of fresh water or the total fresh water in or out of the oceans. E-P determines surface salinity of the ocean, which helps determine the stability of the water column. Salinity and temperature determine the density of ocean water, and density influences the circulation. E-P determines surface salinity of the ocean, which helps determine the stability of the water column. Precipitation also affects the height of the ocean surface indirectly via salinity and density.
The ocean surface is constantly being stirred up by wind and changes in density or buoyancy. The ocean naturally has different physical characteristics with depth. As depth increases, temperature decreases because the sun only heats surface waters. Warm water is lighter or more buoyant than cold water, so the warm surface water stays near the surface. However, surface water is also subject to evaporation. When seawater evaporates, water is removed, salt remains, and relatively salty water is left behind. This relatively salty water can float at the surface; for example, in the tropics it floats because is it so warm and buoyant.
At the surface of the ocean, mixing by the wind can change the density to the point where the temperature and salinity are constant throughout the mixed layer. The depth of the mixed layer is called the mixed layer depth. Phytoplankton in the ocean can impact this mixed layer depth by absorbing the sun's heat at the surface thus decreasing the amount of sunlight that reaches deeper water. In effect, the phytoplankton causes the heating to be confined to a thin layer near the surface and reduces the thickness of the mixed layer.
At higher latitudes, sea water tends to be salty because of poleward transport of tropical water and to a lesser extent, sea ice formation. When sea ice forms, the salt is not crystallized in the ice, leaving the remaining waters relatively salty. Also, near the poles, the seawater is cold and dense. The interaction between water temperature and salinity effects density and density determines thermohaline circulation, or the global conveyor belt. The global conveyor belt is a global-scale circulation process that occurs over a century-long time scale. Water sinks in the North Atlantic, traveling south around Africa, rising in the Indian Ocean or further on in the Pacific, then returning toward the Atlantic on the surface only to sink again in the North Atlantic starting the cycle again.
Generalized model of the thermohaline circulation: 'Global Conveyor Belt' This illustration shows cold deep high salinity currents circulating from the north Atlantic Ocean to the southern Atlantic Ocean and east to the Indian Ocean. Deep water returns to the surface in the Indian and Pacific Oceans through the process of upwelling. The warm shallow current then returns west past the Indian Ocean, round South Africa and up to the North Atlantic where the water becomes saltier and colder and sinks starting the process all over again.
NASA & The Water Cycle
Water is an integral part of life on this planet, and NASA plays a major role at the forefront of water cycle research. Currently, there are many NASA missions that are simultaneously measuring a myriad of Earth's water cycle variables; Evaporation, Condensation, Precipitation, Groundwater Flow, Ice Accumulation and Runoff. NASA's water cycle research missions can be grouped into 3 major categories; Water Cycle, Energy Cycle, and Water and Energy Cycle Missions. By studying each and every variable of Earth's water and energy cycles, "As Only NASA Can", a crucial understanding of the water cycle's effect on global climate is currently underway.
NASA's goal is to improve/nurture the following global measurements: precipitation (P), evaporation (E), P-E and the land hydrologic state, such as soil-water, freeze/thaw and snow. Through NASA's water cycle research, we can understand how water moves through the Earth system in the hydrological cycle and we will be in a better position to effectively manage this vital renewable resource and help match the natural supply of water with human demands. NASA is the only national agency that has the ability to support a full range of water cycle research, from large-scale remote sensing to in-situ field observations, data acquisition and analysis, and prediction system development.
As water travels through the water cycle, some water will become part of The Global Conveyer Belt and can take up to 1,000 years to complete this global circuit. It represents in a simple way how ocean currents carry warm surface waters from the equator toward the poles and moderate global climate.
More NASA Missions and Instruments planned to help better understand the workings of the water cycle. Within the next decade, an experimental global water and energy cycle observation system combining environmental satellites and potential new exploratory missions - i.e. advanced remote sensing systems for solid precipitation, soil moisture, and ground water storage - may be feasible. These proposed new approaches are tantalizing, for knowledge of global fresh water availability under the effects of climate change is of increasing importance as the human population grows. Space measurements provide the only means of systematically observing the full Earth while maintaining the measurement accuracies needed to assess global variability.
Sea Surface Salinity (SSS) is a key tracer for understanding the fresh water cycle in the ocean. This is because whereas some parts of the water cycle increase salinity, other parts decrease it. Global SSS patterns are governed by geographic differences in the "water budget." Like on continents, some latitudes of the ocean are "rainy" whereas others are arid and "desert-like." In general, latitude zones dominated by precipitation have low SSS and those dominated by high evaporation have high SSS. The lowest SSS occurs in temperate latitudes (40 - 50 degrees North and South), near coasts and in equatorial regions and the highest SSS occurs at about 25 - 30 degrees North and South latitude, at ocean centers and in enclosed seas.
To track changes in SSS patterns over time, scientists monitor the relationship between evaporation and precipitation in the oceans. After the launch of Aquarius in 2008, scientists will be able to produce accurate maps of global (E - P). Thus, for the first time we will observe how the ocean responds to variability in the water cycle, from season-to-season and year-to-year.
NASA's Aqua mission contributions to monitoring water in the Earth's environment will involve all six of Aqua's instruments: the Atmospheric Infrared Sounder (AIRS), the Advanced Microwave Sounding Unit (AMSU), the Humidity Sounder for Brazil (HSB), the Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E), the Moderate Resolution Imaging Spectroradiometer (MODIS), and Clouds and the Earth's Radiant Energy System (CERES). The AIRS/AMSU/HSB combination will provide more-accurate space-based measurements of atmospheric temperature and water vapor than have ever been obtained before, with the highest vertical resolution to date as well. Since water vapor is the Earth's primary greenhouse gas and contributes significantly to uncertainties in projections of future global warming, it is critical to understand how it varies in the Earth system.
Frozen water in the oceans, in the form of sea ice, will be examined with both AMSR-E and MODIS data, the former allowing routine monitoring of sea ice at a coarse resolution and the latter providing greater spatial resolution but only under cloud-free conditions. Sea ice can insulate the underlying liquid water against heat loss to the often frigid overlying polar atmosphere and also reflects sunlight that would otherwise be available to warm the ocean. AMSR-E measurements will allow the routine derivation of sea ice concentrations in both polar regions, through taking advantage of the marked contrast in microwave emissions of sea ice and liquid water. This will continue, with improved resolution and accuracy, a 22-year satellite record of changes in the extent of polar ice. MODIS, with its finer resolution, will permit the identification of individual ice floes, when unobscured by clouds.
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The water cycle describes the movement of water on the surface of the earth. Its a continuous process that includes six steps. They are evaporation, transpiration, condensation, precipitation, runoff, and percolation.
Evaporation is the process of a liquid turning into gas or water vapor. Water from oceans, lakes, rivers, or any other bodies of water rises up and evaporates. Transpiration is the same as this but it evaporates from the leaves of plants instead of bodies of water.
Then, condensation occurs. This changes the state of water from gas to liquid. After water rises up into the atmosphere, it condenses or forms clouds.
Soon the clouds become very heavy and then precipitation happens. This is the process of a liquid coming down as rain, sleet or snow.
This creates runoff which is water that travels on the surface and fills up bodies of water. Sometimes this water turns into ground water or water that is soaked up into the ground. This process is called percolation. Water flows downward under the layers of the soil.
This ends the water cycle. Then, it starts again.
This is a link that shows you the steps of the water cycle.
This is another website that shows you what goes on in the water cycle and how it works.
These diagrams show the processes of the water cycle.
Water is essential for life as we know it. It is present throughout the Solar System, and was part of the Earth from its formation. The source of the water was the same as the source of the Earth's sedementery rock goes into a process of retailation
rock : the cloud of particles which condensed in the origin of the solar system.[1]
The water cycle
- The cycle starts when water on the surface of the Earth evaporates. Evaporation means the sun heats the water which turns into gas.
- Then, water collects as water vapor in the sky. This makes clouds.
- Next, the water in the clouds gets cold. This makes it become liquid again. This process is called condensation.
- Then, the water falls from the sky as rain, snow, sleet or hail. This is called precipitation.
- The water sinks under the surface and also collects into lakes, oceans, or aquifers. It evaporates again and continues the cycle.
The present-day water cycle at Earth’s surface is made up of several parts. Some 496,000 cubic km (about 119,000 cubic miles) of waterevaporates from the land and ocean surface annually, remaining for about 10 days in the atmosphere before falling as rain or snow. The amount of solar radiation necessary to evaporate this water is half of the total solar radiation received at Earth’s surface. About one-third of the precipitation falling on land runs off to the oceans primarily in rivers, while direct groundwater discharge to the oceans accounts for only about 0.6 percent of the total discharge. A small amount of precipitation is temporarily stored in the waters of rivers and lakes. The remaining precipitation over land, 73,000 cubic km (17,500 cubic miles) per year, returns to the atmosphere by evaporation. Over the oceans, evaporation exceeds precipitation, and the net difference represents transport of water vapour over land, where it precipitates as rain or snow and returns to the oceans as river runoff and direct groundwater discharge.
The various reservoirs in the water cycle have different water residence times. Residence time is defined as the amount of water in a reservoirdivided by either the rate of addition of water to the reservoir or the rate of loss from it. The oceans have a water residence time of 3,000 to 3,230 years; this long residence time reflects the large amount of water in the oceans. In the atmosphere the residence time of water vapour relative to total evaporation is only about 10 days. Lakes, rivers, ice, and groundwaters have residence times lying between these two extremes and are highly variable.
There is considerable variation in evaporation and precipitation over the globe. In order for precipitation to occur, there must be sufficient atmospheric water vapour and enough rising air to carry the vapour to an altitude where it can condense and precipitate. Precipitation and evaporation vary with latitude and their relation to the global wind belts. The trade winds, for example, are initially cool, but they warm up as they blow toward the Equator. These winds pick up moisture from the ocean, increasing ocean surface salinity and causing seawater at the surface to sink. When the trade winds reach the Equator, they rise, and the water vapour in them condenses and forms clouds. Net precipitation is high near the Equator and also in the belts of the prevailing westerlies, where there is frequent storm activity. Evaporation exceeds precipitation in the subtropics, where the air is stable, and near the poles, where the air is both stable and has a low water vapour content because of the cold. The Greenland Ice Sheet and the Antarctic Ice Sheet formed because the very low evaporation rates at the poles resulted in precipitation exceeding evaporation in these local regions.
