Water equivalent

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The water equivalent (WE) is the amount of water in mm that would be obtained if one were to melt a snowpack of known height and density .

A 1 m thick blanket of fresh snow (density of about 100 kg / m³ or 0.1 g / cm³) results in a water equivalent of 10 cm (100 mm). In other words: if a forecast model shows a rainfall of 100 mm, this corresponds to about 1 m of fresh snow. The density can, however, vary greatly, depending on the conditions in the air layers through which the snow fell: Variations between 30 kg / m³ (dry, loose fresh snow) and 200 kg / m³ (heavily bound fresh snow) are possible.

A snowpack that has been lying for a longer period of time gradually thickens, so that the water equivalent increases, i.e. the amount of water produced per centimeter of snow depth when melting increases, but not the total amount of water in the snowpack. The total amount of water decreases slightly due to evaporation even with older snowpacks, and also very strongly when there is considerable evaporation due to a foehn storm.

If rain falls on a thick blanket of snow, it is initially stored by the snow. The water equivalent per centimeter of snow depth increases, as does the total amount of water in the snowpack.

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