When the ground, dispersing heat by radiation, reaches dew point, the air that is directly in contact with it, condenses and deposits drops of water directly on the ground, and on all the surfaces the air comes into contact with, thus forming dew.
Dew supplies a quantity of water that can be important in some particular situations: where there is no direct precipitation, the vegetation however receives an amount of water that is sufficient for its vital processes. For this reason these are known as occult precipitations, i.e. they are not directly visible. It is not easy to evaluate their quantity, but these precipitations must be taken into account when calculating the ideological balance of the water cycle. In fact dew is partly absorbed by the ground, and a part of it evaporates during the day, and thus becomes part of the water-cycle once again. This type of water supply is fundamental for the survival of plants and animals in arid, semi-desert zones.

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