What is the Water Cycle?

What Does Water Cycle Mean

It is known as the water cycle or hydrological cycle to the process of water circulation between the different compartments that make up the hydrosphere . It constitutes one of the most important biogeochemical circuits on planet Earth , in which water undergoes a series of physical movements and transformations, through which it goes through the three states of matter : liquid , solid and gas .



Water is one of the most abundant substances on the planet, in fact it covers most of it, which is why it is known as the "blue planet" (since it looks bright blue from outer space). On Earth, the largest fraction of water is in a liquid state: 71% of the earth's surface is covered by liquid water , of which 97% corresponds to salt water that forms the oceans. The second most important fraction is that found in a solid state, that is, accumulated as ice: glaciers and polar ice caps located mainly in Greenland and Antarctica occupy 10% of the planet's surface and represent 69% of available fresh water. . Finally, an even smaller fraction of water is in the gaseous state, as water vapor, forming part of the atmosphere : atmospheric humidity represents only 0.001% of the total water on Earth.

Various environmental factors intervene in the hydrological cycle, such as wind and solar energy (the latter being the main driver). Like any cycle, it does not really start at any specific point, but rather it is a continuity of processes that are repeated successively . Just for the purpose of explaining it, a "starting point" is set.

The water cycle begins with the evaporation of water from the surface. Then, as it rises, the water vapor contained in the air begins to cool and condenses into small drops of water, which gather to form clouds. The clouds move and collide with each other, until at some point there is precipitation, produced by the weight of the water itself. When the temperature of the atmosphere is very low, precipitation can fall as ice or snow.

Of the water that reaches the earth's surface, one part feeds the oceans and other bodies of water and another is directly used by living beings . A third fraction of the water that precipitates seeps through the soil and accumulates forming aquifers or layers of groundwater, which can eventually re-emerge as sources or as part of different bodies of water (such as streams or rivers). Sooner or later, the water evaporates again and the cycle begins again.

The water cycle is vital for the maintenance and stability of our planet , not only for life but also for the regularity of the climate , the global temperature and other conditions that determine the planetary reality. If this cycle were to stop for some reason, the effects would be catastrophic: hot regions would take much longer to cool, water would stagnate in oceans and lakes, and all life would suffer.

Can serve you: Iceberg

Stages of the water cycle

The melting of ice is an example of melting.

The water cycle is made up of the following successive and simultaneous stages, which are constantly repeated and interpenetrate with each other:

  • Evaporation . Liquid water in the oceans and other bodies of water evaporates from a liquid to a gaseous state, thanks to the action of sunlight and the daily heating of the Earth. Living beings also contribute to the evaporation process, through perspiration in the case of plants and sweating in the case of animals. The oceans provide 90% of the water vapor in the atmosphere , while living beings, especially plants, provide the same. Lakes and rivers contribute a smaller percentage and an even smaller one is glaciers and sea ice that, being in very cold climates to become water, sublimate instead of evaporating (they go from solid to gaseous directly).
  • Condensing . Water in the atmosphere travels enormous distances, being scattered by the winds in different directions. When water vapor reacheshigher altitudes , the lower temperature allows it to condense, that is, to regain its liquid form and form water droplets that accumulate in darker and darker clouds as they contain more and more water droplets. .
  • Precipitation. When the water droplets contained in the clouds are already large and heavy enough, they break their state of equilibrium and rain or precipitation occurs. Generally, water falls in a liquid form, but in certain regions and climatic conditions where temperatures are lower, it can fall in a more or less solid form, such as snow, frost or hail.
  • Infiltration. The water that reaches the terrestrial soil penetrates through it and is transformed into groundwater. The amount of water that filters through the surface depends on different factors such as the permeability of the soil , the slope and the vegetation cover of the region. The infiltrated water can then return to the atmosphere by evaporation or be incorporated into different bodies of surface water.
  • Runoff Liquid water is moved downhill across the surface of the terrain through various methods . Runoff is capable of generating erosions and transporting sediments.
  • Underground circulation. Like runoff, water moves with gravity , toward where the ground is sloping. In this case, the water seeps through the pores in the earth and then travels underground, sometimes even through permeable rocks.
  • Fusion. It refers to the transformation of water from its solid state (ice or snow) to liquid, when thawing occurs. Thus, the melting of ice in warm seasons, as occurs at the poles and in frozen continental regions, returns the water to its initial point in the cycle.
  • Solidification. It consists of the passage of water from the liquid to solid state and occurs when the temperature is less than 0 ºC. The solidification process can occur in clouds, leading to the formation of snow or hail, and also on the surfaces of lakes and rivers, when temperatures are low enough.
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