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5.6: Our Water Supply

Water is essential to life.  Humans require fresh water to live and to irrigate our crops -- yet, only about 2.5% of the water on earth is freshwater.  In California the problem is even more extreme.  If you look at the Average Annual Precipitation maps on page 72 of Goodes World Atlas, you will note that the western half of the United States receives far less precipitation than the eastern half.  Note also in the ‘Moisture Regions’ figure that most of the west is listed as being a ‘dry climate, with the majority of southern California considered semiarid or arid.  This becomes a major issue when you recognize that California is the most populous state in the union.  Where are we getting our fresh water?

Unlike the eastern United States, California does not have a large underground aquifer.  The small aquifer that was under the Great Central Valley was mostly depleted within the first 100 years of farming the region.  So where do we get our water?  Look again at the figure of Precipitation from November 1 to April 30 in Goodes World Atlas.  Note the band of dark green and blue (20-40 in, and 40+ in) in the northeastern part of California.  This represents the Sierra snow pack. 

California harvests the melt water from the Sierra snow pack through an elaborate network of dams, reservoirs and canals (recall the map of dams from the ICE maps in chapter 2?).  These direct the water from where it is precipitated (in the Sierra Nevada mountains) to where there is a high demand for it:  in agriculture in the Central Valley, and in urban areas such as the San Francisco Bay Area and Los Angeles.  This is officially called as the State Water Project, and it has been called by someone of the world’s most ambitious public works projects, and by others an enormous environmental disaster.

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