Water supply and demand

Agriculture plays an important part in California's economy and irrigation water is an essential factor in agriculture's success. However, California faces serious water supply issues, in which agricultural uses must compete with environmental uses and the demands of a growing population. Several options are open to policymakers regarding the state's supply, demand and transport of water. California's primary source for water is precipitation-rain and snowfall. In a normal precipitation year, the state will receive about 200 million-acre-feet (maf) in precipitation and imports from Colorado, Oregon and Mexico (DWR 2009, 1-4). Of the total supply, about 60 percent is used directly by vegetation or cropland or flows to salt sinks like saline aquifers or the Salton Sea. The remaining 40 percent, or about 80 maf, enters stream flows or wells and is distributed among agricultural, urban and environmental uses (DWR 2009, 1-4). About 30 maf is used for agricultural irrigation and about 9 maf enters urban and industrial uses. Most of the precipitation occurs in the north and east of the state. However, irrigation water demand is highest in the state's valleys and coastal plains so a storage and transport system was developed to capture this runoff and deliver it during the dry months. California has more than 1,200 surface water reservoirs, in addition to an extensive network of canals, levees, and treatment plants (see Figure 1). Since most of the urban demand lies in the south and along the coast, a series of pumps must transport water at great expense over mountain ranges. The irrigation provided by this system, together with the Mediterranean climate through much of the state, allows the cultivation of a great variety of crops. However, precipitation varies significantly from year to year and water supplies are therefore unpredictable. Moreover, current climate change models suggest that the Sierra Nevada snowpack is likely to decrease in the future (Kapnick and Hall 2009). Recently, increased efficiency in usage has also contributed to the state's ability to meet water needs. However, urban and industrial water demand has risen as the population has continued to grow. Urban water usage, including residential, commercial and industrial uses, is about 8.7 million acre feet annually and growing (DWR 2009, 4-10). Environmental and agricultural water usage vary significantly by year, depending on drought conditions. In a typical year, agriculture will irrigate about 9.6 million acres with 34 million acre-feet of water (DWR 2009, 4-10) or …