The atmospherical rainfall (resulted from the condesation and crystallization of water vapours which fall from the clouds in liquid, solid or mixed form) represents one of the most important climatic elements, with noticeable influence on the natural environment of a certain region. Rainfall has an important impact on the environment of terrestrial atmosphere (which is an important link in the water’s nature circuit) and contributes to keeping the soil humid. After all, life wouldn’t have been possible without water, a key element in the formation of terrestrial atmosphere, a real protection against ultraviolet radiations and against strong termic amplitudes. Besides influencing all the other climatic elements, water plays an important part in all earth’s covers by continously modifying the relief (so it is an external factor of modelation), the configuration of hydrographical network and being involved in the formation and development of vegetation, fauna and soils (the biosphere). Like all the other elements, atmospherical rainfall could be seen as either a resource (link in the water’s circuit in nature) or a hazard (when its extremes are beyond normality and bring serious damage to society). Besides pluviometric differences, there is also an alternation of humid sectors which are positioned over the higher areas of the relief with drier sectors, sequence well distinguished on the direction North-West – South-East. Meanwhile, the slopes experiencing the change in masses of air from West and North-West, being more humid, perceive bigger quantities of precipitations while the Southern ones are drier, this also because of the foehn phenomenon.
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