The users of water can be broadly categorized into three groups: urban, agricultural, and fish and wildlife. Very efficient water resource management, which is particularly critical during a drought period, depends upon willingness and opportunity for these three user groups to cooperate. Cooperation could entail, among other things, transferring water supplies among user groups. For fish and wildlife, it also might involve having relaxed environmental regulations during dry periods.
Although there are opportunities to decrease demands in all sectors of society, this discussion will only address agriculture. Various options are available for a farmer whose water supplies have been reduced. The options vary depending on whether the farm grows perennial crops, annual crops, or a combination of the two. Annual crops allow the greatest flexibility because they can be selected based on their seasonal water demand. Crops have different seasonal water demands, and those with the least demand can be selected for planting. Another choice is to not plant a crop but leave the land fallow. Depending upon the available water supply, it may be economically beneficial to restrict the acreage planted and irrigate this acreage to achieve high yields rather than to spread the water on the entire farm with yield reductions in all fields.
Perennial crops have a more critical water need than do annual crops. For perennial crops, the highest priority is to provide sufficient water to keep the crop alive until water supplies increase in future years. Because perennial crops have the highest priority and have limited flexibility, the opportunity to transfer water from annual to perennial crops is desirable. Farms that grow mostly annual crops have the opportunity to greatly reduce their water demands and make water available for other users. However, a mechanism for transferring water is required to make this arrangement feasible.
Some case studies from California on coping with drought will be presented. Each of the case studies involves not only agriculture, but also cooperative arrangements between the agricultural and urban sectors. The vast network of canals in California facilitates the transfer of water between various water users from different locations in the state. Some features of these case studies may not be feasible in other geographic locations that do not have water conveyance systems. In addition, the abundance of both surface and groundwater resources that allow conjunctive use programs may not be present in other places.