Water Planning

There are three main uses of water in California. The use that most of us think of is urban water use. In 1995, Californians used 11% of their water supplies in cities and towns, and the DWR projects that 15% will be used in 2020 (DWR Water Plan Update, Bulletin 160-98, p. 4-2). That’s 4% more water used. How do the water planners know how much water will be used in the future? They use mathematical calculations to average how much water each person uses each day – gallons per capita daily, or gpcd. Then they use the U.S. Census bureau projections (best guesses) to determine how many more people will be living in California in 2020. They are then able to figure out the amount of water used. Counties that are expected to grow the most include Riverside, San Bernardino, Kern, Calaveras, Amador, Sutter, and Del Norte (DWR Bulletin 160-98, p. 4-5). So, is this “urban” water only used in homes? No - urban water use includes businesses, stores, industry and manufacturing, and irrigation for parks and schools.

Another use of Californian water is agricultural water use. Crops use a lot of water – in fact, 43% of all Californian water in 1995. However, DWR forecasts that in 2020, only 39% of all water will be used for agriculture. That’s 4% less water used by agriculture. Can you think of where that water will be used instead? Where did you read 4% before? Will there be an increase in people or an increase in crops in 2020? Why do crops use so much water? Farmers have to make sure that their plants get enough water, so they have to put more water on the fields than what may seem necessary. Evapotranspiration, also called ET, is the process by which plants absorb water from the soil and emit water vapor to the atmosphere through the pores in their leaves (Oberlander & Muller 1982, p. 59). Scientists measure the rate of ET, which is affected by climate, solar radiation, humidity, temperature, wind, type of crop, and the size of the plants’ growth (DWR Bulletin 160-98, p. 4-17). Water planners use the ET information and figure out how much land is planted in specific crops in the state, and are able to calculate how much water will be used for agriculture.

Another important use of the state’s water is environmental water use. Environmental water use was 46% of all state water use in 1995, and is projected to remain the same in 2020. Some rivers in California are specified as Wild and Scenic Rivers – that is, they cannot have dams built on them and they are being “saved” for their free-flowing characteristics. Some of these rivers include Sespe Creek in Southern California; the Tuolumne and Merced Rivers in the Sierras; and the Klamath and Smith Rivers in Northern California. Beneficial uses of instream flows are for fisheries, wildlife, aesthetics (beauty), recreation (rafting), and navigation (boating). Another environmental water use is to benefit the Delta area of California. This is a special place between the San Francisco Bay and Stockton in the Central Valley. It is full of waterways, marshes, and wetlands. It is also full of fish, ducks and other migratory (moves with the seasons) birds, frogs, and bugs. This all-important ecosystem needs to be preserved.