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Water cycle


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Water cycle

  1. 1. The water cycle, also known as the hydrological cycle or H2O cycle, describes the continuous movement of water on, above and below the surface of the Earth. Although the balance of water on Earth remains fairly constant over time, individual water molecules can come and go, in and out of the atmosphere.
  2. 2. There are some processes which take place during the Water Cycle. The processes are- 1. Evaporation 2. Condensation 3. Precipitation 4. Transpiration 5. Surface Runoff
  3. 3. The transformation of water from liquid to gas phases as it moves from the ground or bodies of water into the overlying atmosphere.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.
  4. 4. Water vapor in the air gets cold and changes back into liquid, forming clouds.This is called condensation. You can see the same sort of thing at home... pour a glass of cold water on a hot day and watch what happens. Water forms on the outside of the glass. That water didn't somehow leak through the glass! It actually came from the air. Water vapor in the warm air, turns back into liquid when it touches the cold glass.
  5. 5. Condensed water vapor that falls to the Earth's surface . Most precipitation occurs as rain, but also includes snow, hail, fogdrip, graupel and sleet. 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.
  6. 6. Transpiration is the process by which moisture is carried through plants from roots to small pores on the underside of leaves, where it changes to vapor and is released to the atmosphere.Transpiration is essentially evaporation of water from plant leaves.Transpiration also includes a process called guttation, which is the loss of water in liquid form from the uninjured leaf or stem of the plant, principally through water stomata.
  7. 7. When rain hits saturated or impervious ground it begins to flow overland downhill. It is easy to see if it flows down your driveway to the curb and into a storm sewer, but it is harder to notice it flowing overland in a natural setting. During a heavy rain you might notice small rivulets of water flowing downhill.Water will flow along channels as it moves into larger creeks, streams, and rivers.This picture gives a graphic example of how surface runoff (here flowing off a road) enters a small creek.The runoff in this case is flowing over bare soil and is depositing sediment into the river (not good for water quality).The runoff entering this creek is beginning its journey back to the ocean.
  8. 8.  The water cycle provides natural filtration of water and returns clean fresh water to the earth.When water evaporates, all impurities and contaminants are left behind and only pure water vapor escapes.Without this powerful filtration system, we would soon contaminate all the water on earth and would run out of fresh water.
  9. 9. The water cycle is powered from solar energy. 86% of the global evaporation occurs from the oceans, reducing their temperature by evaporative cooling.Without the cooling, 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.