Hydrological Cycle

Water is always on the move – it is in circulation. In contrast to mineral resources it is not used up but it can be used numerously. The amount of water on the earth and in the aerosphere is estimated at 1,383,844,700 km³. The most part of the water (97.591%) is in the oceans, the inland seas and the salt lakes. It is salt water. Only 2.408% is fresh water. The biggest part of it (78%) is stored in the polar region and the glaciers. The remaining 22% of fresh water is divided into surface water, ground water, ground humidity and water in the biomass. That is an amount of water of 7,326,700 km³ altogether or 0.529% of the entire amount of water on the earth and in the aerosphere. 0.001% or 13,838 km³ or rather 13.8 Billions m³ of water is in the aerosphere. [2]

The most important source for the vegetation is the precipitation of the athmosphere. In the annual average it is 880 mm globally. The earth has a surface of 510 Billions m². Consequently the total precipitation has a volume of 448.8 Billions m³. That is many times of which is in the aerosphere. That’s why the water in the aerosphere renews itself every 11.3 days. [2]

One part of the precipitation evaporates, one part seeps away in the soil and becomes ground water. The part that don’t seeps away or becomes ground water runs off the surface in brooks and rivers that flows into lakes or the sea. The distribution of precipitation on the earth is differently. Where there is much precipitation much water can evaporate, become ground water or it flows away. In the temperate zone the ratio of rainfall to evaporation is steady. During short terms the precipitation in dry areas is lower than the evaporation. During this period of time water shortage, droughts can be caused and therefore about failures of harvest and famines.

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