California rainfall and runoff vary widely throughout the State, and also vary greatly from year to year. The State's historical record of measured runoff amounts to little more than 100 years of data, but other information indicates that California has experienced climatic conditions both wetter and drier than those of the present within the past 1,000 years. Three twentieth century droughts were of particular importance from a water supply standpoint -- the droughts of 1929-34, 1976-77, and 1987-92. The purpose of this report is to review conditions experienced by water agencies during the 1987-92 drought, in light of changed water management circumstances, to identify actions the Department could take to prepare for a drought occurring within the next few years.

The 1987-92 drought was notable for its six-year duration and the statewide nature of its impacts. Statewide reservoir storage was about 40 percent of average by the third year of the drought, and did not return to average conditions until 1994. The Central Valley Project and State Water Project met their contractors' delivery requests during the first four years of the drought, but then were forced by declining reservoir storage to reduce deliveries substantially. The SWP terminated deliveries to agricultural contractors and provided only 30 percent of requested urban deliveries in 1991, the single driest year of the drought. A 1991 Governor's executive order created a Drought Action Team to coordinate a response to deteriorating water supply conditions, and directed the Department to implement a drought water bank. Twenty-three counties had declared local drought emergencies by the end of 1991.

California's population has increased by more than 6 million people since the beginning of the last drought. There have been significant changes in California's water management framework. For example, California water users are now preparing a plan and negotiating associated agreements to reduce use of Colorado River water to California's basic apportionment in years when surplus water is not available. Other changes affect the ability of the CVP and SWP to export water from the Sacramento-San Joaquin River Delta. These changes included the new State Water Resources Control Board Bay-Delta water rights decision, Central Valley Project Improvement Act requirements reallocating project water for environmental purposes, Endangered Species Act listing of five new fish species, and management of water operations through the CALFED Operations Group.

New regional water management facilities constructed since the drought include the Department's Coastal Aqueduct, Mojave Water Agency's Mojave River and Morongo Basin Pipelines, Metropolitan Water District's Diamond Valley Lake, and Contra Costa Water District's Los Vaqueros Reservoir. Five new large-scale groundwater recharge/storage projects have gone into operation; several others are in advance planning stages.

Key findings discussed in the report include:

• Defining when a drought occurs is a function of dry conditions' impacts on water users. The Department used two primary criteria to evaluate statewide conditions during the 1987-92 drought -- runoff and reservoir storage. A drought threshold was considered to be runoff for a single year or multiple years in the lowest ten percent of the historical range and reservoir storage for the same time period at less than 70 percent of average.
  

• Drought is a gradual phenomenon. Most natural disasters, such as floods or forest fires, occur relatively rapidly and afford little time for preparing for disaster response. With the exception of impacts to dryland farming and grazing, drought impacts occur slowly over multi-year periods, and increase with the length of dry conditions. Adverse impacts can be reduced by planning appropriate response actions prior to drought onset. The Urban Water Management and Planning Act, for example, requires California's larger urban water suppliers to develop contingency plans for shortages of up to 50 percent.
  

• Most Californians would experience minimal water supply impacts from a single dry year, thanks to the State's extensive system of water infrastructure. Most of California's major urban and agricultural production areas -- with the exception of the Salinas Valley -- are within reach of a regional conveyance facility or natural waterway that would provide access for water transfers or exchanges. The Santa Barbara metropolitan area, the largest urban area to experience major water supply impacts during the 1987-92 drought, is now connected to the State's system of water infrastructure via the State Water Project's Coastal Aqueduct.
  

• Past droughts demonstrated that water users affected the earliest and to the greatest extent by drought conditions were those not connected to the State's system of water supply infrastructure, but reliant solely on annual rainfall. Typical examples were rural residents supplied by marginal wells, isolated communities relying on springs or small creeks, and ranchers dependent on dryland grazing. Residential water users and small water systems experiencing the most problems were those located in isolated North Coast communities and in the Sierra Nevada foothills. Water haulage and drilling new wells were typical drought response actions in these areas.
  

• The area at most economic risk from a single dry year would be the west side of the San Joaquin Valley, where dry hydrologic conditions would exacerbate federal water contractors' shortages associated with CVPIA implementation and Delta export restrictions. Significant socioeconomic impacts to low-income Westside farming communities were attributed to the last drought.
  

• Groundwater extractions increase substantially during droughts. The total number of well construction/modification reports filed with the Department was in the range of 25,000 reports per year during the last drought, up from fewer than 15,000 reports per year prior to the drought. Most new wells were for individual domestic supply. Rural homeowners with private wells are largely an unserved population with respect to drought-related assistance programs, although they constituted many of the public information requests directed to the Department during the last drought. The Department should implement drought outreach programs for these water users.
  

• Virtually all the State's larger water agencies implemented short-term demand management actions to respond to the last drought. The effects of demand hardening on water agencies' ability to implement shortage contingency measures should be monitored. Statewide, the acreage of perma- nent agricultural plantings that require water during drought years -- such as orchards and vineyards -- has increased. Most of the increased acreage is located in the San Joaquin Valley, much of it within the water-short CVP Delta export service area. As urban water agencies implement plumbing fixture retrofit programs or have greater percentages of new housing stock with low water use fixtures, it becomes increasingly difficult for the agencies to implement rationing programs without affecting customers' lifestyles.
  

• Changed Delta regulatory conditions have rendered the Department's 1993 drought water bank programmatic environmental impact report outdated. A future bank's scope would likely differ from that of the Department's previous banks. Almost 30 percent of California's counties now have local groundwater management ordinances; most ordinances restrict or control groundwater export from a county. Groundwater substitution transfers were a major source of the water purchased by the drought water bank. The proliferation of new county ordinances makes it less likely that the water bank, or local agencies seeking drought water supplies through transfers, would be able to implement transfers involving groundwater.
  

• Making specific plans for longer-term drought preparedness is complicated by Bay-Delta water management uncertainties. SWRCB's Bay-Delta water rights hearing process remains to be completed. The CALFED program is in a transitional state from planning to implementation, with a decision on its environmental documentation scheduled for later this year. The Bay-Delta Accord will expire in September 2000; discussions are ongoing as to the governance structure that could replace it, including how the function now performed by the CALFED Operations Group might be institutionalized.
  

• Despite uncertainties associated with Bay-Delta water project operations, having conceptual plans for multi-year operations is an important aspect of drought preparedness. The CALFED Operations Group has been focused on short-term operations under wet hydrologic conditions, responding to day-to-day Delta fishery requirements in the Delta. The last drought demonstrated the need for conservative management of carry-over storage during dry periods. The Department should work with the CALFED Operations Group or its successor entity, and with the drought panel to be appointed by the Governor as part of CALFED's Bay-Delta Program, to begin conceptual development of multi-year SWP and CVP operations strategies.
  

• Implementation of many larger agencies' drought response plans is dependent on access to convey-ance capacity -- in either their own or in other agencies' facilities. The California Aqueduct often figures prominently in such plans, because it is the only facility linking Northern California water supplies with Southern California water users. Availability of aqueduct capacity for wheeling non-project water is becoming increasingly constrained by Delta export restrictions, as well as by contractual commitments and increasing SWP contractors' water demands. The growing number of south-of-Delta groundwater recharge/storage programs further contributes to wheeling requests. Considering the increasing level of interest in aqueduct wheeling, it may now be time for the Department to adopt a formal priority system for access to aqueduct capacity.