Extensive evaluation and analyses of water demands were conducted to complete Bulletin 160-93. These analyses recognize the water demands of all beneficial uses: urban, agricultural, environmental, and other uses including water based recreation and power generation. An overview of these demands follows.
Urban water demand forecasts are primarily based on statewide population projections that show an increase of almost 19 million people from 1990 to 2020, from roughly 30 million to 49 million people. About half the projected population increase will happen in the South Coast Region. Population projections for the California Water Plan Update are based on the Department of Finance baseline series. The DOF population estimates are taken from the 1990 census as the base year. Figure ES-6 shows projections of population.
Urban annual net water demand could increase from 6,800,000 af in 1990 to 10,500,000 af by 2020, after accounting for implementation of conservation measures that are expected to reduce urban annual net water demand by about 900,000 af. Urban water demand forecasts are based on: population projections, unit urban water use values--considering probable effects of future water conservation measures, and housing trends, such as increases in multi-family housing and greater growth in warmer inland areas of the State. Table ES-3 shows urban water demand forecasts by hydrologic region.
Urban water agencies recognize the need for better demand forecasting methods to estimate water use. Some water agencies are moving toward a more disaggregated approach, similar to that of energy utilities. DWR and the University of California at Los Angeles have evaluated forecasting methods and developed procedures to estimate conservation from Best Management Practices. In this approach, data about the end uses of water are analyzed individually and then aggregated together to forecast overall water use. The benefits from implementing BMPs were evaluated and included in Bulletin 160 estimates of future urban water use. Statewide, implementation of BMPs could reduce urban annual applied water demand by about 1,300,000 af by 2020. The annual net water use and depletion reduction from BMPs could amount to 900,000 af and is included in the urban water demand forecasts shown in Table ES-3. The 900,000 af is in addition to 400,000 af of annual net savings resulting from conservation measures put in place between 1980 and 1990. However, more water use information must be gathered to further refine urban demand forecasting and evaluation of BMP effects on future water demand. Specific recommendations presented in Bulletin 160-93 are:
To compute agricultural water demand, Bulletin 160-93 analyses integrated the results of three forecasting methods used to estimate irrigated acreage and crop type:
Every five to seven years since 1948, DWR has physically surveyed agricultural land use to help assess the locations and amounts of irrigated crops. Acreages of crops grown are estimated on a yearly basis, using the annual crop data produced by county Agricultural Commissioners, adjusted on the basis of DWR land use surveys, and estimates of urban expansion onto irrigated agricultural land (see Figure ES-7).
The Crop Market Outlook is an economic model that uses data based on the expert opinion of bankers, farm advisors, commodity marketing specialists, and others regarding trends in factors affecting crop production in California. Several factors are evaluated, but the four primary ones are: (1) the current and future demand for food and fiber by the world's consumers; (2) the shares of the national and international markets for agricultural productions that are met by California's farmers and livestock producers; (3) technical factors, such as crop yields, pasture carrying capacities, and livestock feed conversion ratios; and (4) competing output from dryland (non-irrigated) acres in other states. The results determine the forecasted future potential California production of various crops.
The Central Valley Production model is an economic model that accounts for crop production costs in different areas of the Sacramento and San Joaquin valleys in conjunction with the effect of overall production levels on the market prices for California crops. This helps to estimate how the total California production will be distributed among counties.
Some crop shifts are expected to happen as growers move from low price to high price crops. Alfalfa and pasture lands are forecasted to decrease by about 331,000 acres mostly in the San Joaquin and Tulare Lake regions. Crop acreages expected to increase include vegetables, nuts (almonds and pistachios), and grapes. While the acreage of low-quality (bulk) wine-grape acreage is decreasing in the San Joaquin Valley, the acreage of high-quality table wine grapes is increasing in other regions.
The 1990 level crop acreage and crop types are based on agricultural land use surveys which were normalized to take into account the impact of the 1987-92 drought, government set aside programs, and other annual crop acreage fluctuations. Forecasts of agricultural water needs are based on: (1) agricultural acreage forecasts, (2) crop type forecasts, (3) crop unit applied water and unit evapotranspiration of applied water values (in acre-feet for each crop acre), and (4) estimates of future water conservation.
Agricultural water needs were evaluated by determining crop types and acreages for each region. Forecasts indicate that irrigated agricultural acreage will decline by about 378,000 acres between 1990 and 2020, from 9,178,000 acres to about 8,800,000 acres. This decline represents a 700,000-acre reduction from a peak in 1980.
Many of agriculture's unit applied water values have decreased during the past decade. For the State as a whole, agricultural annual net water demand will decrease by about 1.9 maf, from 26.8 maf in 1990 to 24.9 maf in 2020. Part of this decrease is due to improvements in irrigation efficiency and increased emphasis on water conservation since the 1976-77 drought. Table ES-4 shows the 1990 level and future agricultural water demands by hydrologic region. Bulletin 160-93 put forth the following recommendations for better assessing agricultural water demand:
Estimates of environmental water demand are based on: water needs of managed fresh water wetlands and the Suisun Marsh, environmental instream flow needs, Delta outflow, and wild and scenic rivers. Wetlands water needs were tabulated from: (1) investigations of existing public and private wildlife refuges; and (2) additional water for wetlands as required by the CVPIA. Environmental instream flow needs were compiled by reviewing existing fishery agreements, water rights, and court decisions pertaining to water needs of aquatic resources of streams. Additional flows in the Trinity River, as noted in the CVPIA, are also included in forecasts of environmental instream demand.
Environmental water needs in drought years are considerably lower than in average years, reflecting the variability of the natural flows of rivers and lower fishery flow requirements, such as in D-1485 for the Bay-Delta. Table ES-5 shows California's regional environmental net water demands.
Regulatory agencies have proposed a number of changes in instream flow needs for major rivers, including the Sacramento and San Joaquin. These proposed flow requirements are not necessarily additive; however, an increase ranging from 1 to 3 maf is presented to envelop potential environmental water needs that could result from proposed additional instream flows and actions under way by regulatory agencies (see Figure ES-8). Bulletin 160-93 recommends the following to better assess environmental water needs:
Table ES-6 shows California's net water demands; these include reductions in demand due to long-term conservation measures for both urban and agricultural users and reductions due to land retirement in San Joaquin Valley areas with poor drainage. A majority of the environmental net water demand occurs in the North Coast hydrologic region, indicating the large dedicated natural flows of the North Coast wild and scenic rivers system, about 17.8 maf in an average year. Dedicated instream flow under D-1485 makes up the largest portion of the San Francisco Bay Region's net water demand, about 4.6 maf, while urban and agricultural net water demands for the region amount to 1.3 maf. The South Coast Region has the highest net water demand for urban use, about 3.5 maf in an average year, and the Tulare Lake Region has the largest net water demand for agriculture, about 7.7 maf in an average year.
