Water cycle

The term water cycle refers to the transport and storage of water at the global and regional level. Here, the water changes several times its physical state and goes through the various spheres such as the hydrosphere, lithosphere, biosphere and atmosphere of the Earth. The circulation of water takes place usually between the sea and the mainland. In the water cycle, no water is lost, it just changes its state. These states are represented by the water balance and consequently accounted for in the water balance.

General diagram of a water cycle

The oceans are the largest water reservoir of the earth, they cover most of the earth's surface. Solar energy heats the water. Through evaporation, especially at the sea surface, to a lesser extent, on the mainland, creates humidity. Because this steam is lighter than air, it rises upward into the atmosphere. There is colder than on the ground, therefore, the water vapor is cooled and condensed. This creates clouds. The wind carries the moist air to the mainland. When the moist air meets cold air layers, so she pushes at it, and rises to ( warm front ), as well as it encounters mountain flanks ( convection). When the air rises, it cools. Cold air can also absorb less moisture than warm. When the clouds are already so saturated with condensed water, it comes to rainfall, and the water falls as rain, snow or hail back to Earth. The shape of the precipitate depends on the temperature. If the precipitation falls directly into surface waters, closes the circuit and can start over again. If the water on the earth, it seeps into the groundwater. Then via the groundwater flow or springs and rivers flowing into the oceans. Also, water from melting glaciers and snow and superficial abgeführtes rainwater is transported via rivers to the oceans. In the polar areas and high mountain part of the precipitation is stored in solid form as ice, where it passes through melt water back into the oceans.

Basic equation of the water cycle

Simplistically, can the water cycle described by the following basic equation:

The entry by rainfall N drainage results in A and evaporation V. However, the representation used here is just a simplified example of a water balance equation.

Water on other celestial bodies

According to some scholars there is water with high probability on other celestial bodies in the solar system such as Mars.

The cycle of water is generally regarded as a prerequisite for life.

History

Throughout human history the circulatory character of water has long been recognized, or at least guessed. That the related principle is " Panta Rhei " - everything flows. Even in the Bible several times made ​​to the water cycle reference or described extreme precipitation in the flood.

Various theories about the water cycle and its drive:

  • Neous meteoric water cycle: theory to the water cycle according to current understanding, which was probably founded by Xenophanes and has, among other things, Diogenes of Apollonia and Hippocrates as an early representative.
  • Theory of salt water ascent: reversal of the flow direction of the meteo neous water cycle, after the earth rests on the waters of the seas and this all above-ground sources fed. This theory was founded by Thales and had Hippon and Plato as an early representative.
  • Theory of formation water from the air: The water comes from the air (effect of condensation) and would feed the sources of the rivers on the precipitate. This theory was developed by Aristotle and presented the authoritative doctrine to the early 17th century dar.
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