How Much Water in an Inch of Snow?
If the snowfall amounts were translated into equivalent volumes of water - then how much water would that be? Using a rule of thumb that each 10 inches of snow, if melted, would produce one inch of water, then each inch of snow produces about 2,715 gallons of water per acre. Of course, the actual amount can vary considerably depending on whether the snow is heavy and wet or powdery and dry, so this is based on the 'average' water content of snow.
Heavy, wet snow has a very high water content and 4 or 5 inches of heavy, wet snow can contain about one inch of water, while it may take 20 inches of dry, powdery snow to equal one inch of water. The 10=1 equation also assumes a 'perfect' snowmelt without evaporation or other losses. So how many gallons of water would that be for, say, Chicago?
An inch of snow that falls evenly over the 1,358,599 acres of the 'urbanized area' (acreage based on 2000 Census Bureau list of urbanized areas) of Chicago, Ill., is equivalent to about 3,689 million gallons of water (or 3.69 billion gallons). The snowpack that accumulates each year in the mountains across the country are a vital part of the hydrologic cycle, according to USGS hydrologists. The snows that melt off each spring provide essential runoff to streams and reservoirs and provide recharge to the nation's ground-water reservoirs as the ground thaws and the snows melt and filter downward into the aquifers (water-bearing rock formations).
NASA Office of Space Science