The Earth is a planet like any other solar system. To our knowledge, is the only one that has evolved life. The main reason for this uniqueness is its position on the Sun This position determines in a precise manner the Earth’s climate, a climate that was conducive to the emergence of life. But the climate is the result of a balance between water constantly readjusted, the atmosphere and energy of the sun’s solar energy, which keeps the masses of moving water between land, sea and atmosphere, makes engine water cycle. We thus show the close link between climate and land on Earth, water is present in all its forms: liquid, ice or steam. It is divided into five interconnected reserves, which together constitute the hydrosphere.
The sea is the most important of these reserves, followed by deposits of ice or snow, ground water, atmosphere and ultimately the biosphere. More precisely, the sea contains 1350 x 1015 m3 of water is say, 97% of all the water in the hydrosphere. The continents have 33.6 x 1015 m3, mainly located in the Arctic and Antarctic ice. The atmosphere has only one hundred thousandth part of the water content of the climate system: 0.013 x 1015 m3. You may consider this figure to cause some surprise.
The abundance of rainfall and its influence on climate and water resources, does not seem commensurate with the minimum amount of water present in the atmosphere at a given time. On the continents, water is distributed among various reserves, the most important of which, and by far, is formed by glaciers (25 x 1015 m3) totaling about 1.8% of the hydrosphere, then come the surface waters (8.4 x 1015 m3), lakes and rivers (0.2 x 1015 m3) finally living matter of the biosphere (0.0006 x 1015 m3. In the deposits formed by groundwater, water soaking the soil (tile) represent only 0.066 x l0l5 m3.El rest is distributed almost evenly between deposits of depth less than or equal to 800 meters. These sites are subject to constant transfers of large amounts of water within the climate system. We all have an intuitive notion of the water cycle, at least in broad outline: evaporation, precipitation, water courses. Everything comes from the sea and everything returns to the sea in one way or another. The residence time of water in each type of reservation can be calculated from the amount of water present in the said reserve and its rate of accumulation or disappearance. In the atmosphere, the residence time is about nine days in polar ice and sea, however, is several thousand years.