Drought Background

What is Drought?

No simple, precise definition of drought exists. In general, a drought is an extreme event characterized by a prolonged period of abnormally low levels of precipitation that has adverse impacts on vegetation, animals, and people. A drought is a temporary phenomenon and as such, it is distinct from aridity, which is a climatic feature of a particular region. Droughts occur periodically in every climatic zone, although some areas are more drought-prone than others.

Droughts in California

Droughts are a recurring feature of California’s climate. In the last century, the most significant statewide droughts occurred in 1929-1934, 1976-1977, 1987-1992, and 2012-2016, and a less severe drought occurred in 2007-2009. The 2012-2016 drought was one of extreme proportions, with record-high temperatures and record-low levels of snowpack and precipitation.

Droughts have social, economic, and environmental implications. Here is a short summary of some of the impacts that typically occur during a drought:

  • Water Supply and Quality. Drought negatively impacts both the quantity and quality of water supplies. While a reduction in water supply is generally a temporary phenomenon, it can be permanent in some instances. Groundwater overdraft, for example, can cause land to sink, resulting in a permanent loss of groundwater storage. Drought can also compromise water quality, such as by concentrating salts and other contaminants, reducing dissolved oxygen levels, and increasing water temperatures. Water quality problems can exacerbate water supply problems.
  • Fish and Wildlife. Political pressures increase diversions of water away from ecosystems. As water levels in streams, rivers, and lakes decline, fish and wildlife are at risk of dying, potentially causing regional extinctions. Fish in the Sacramento-San Joaquin river delta (the “Delta”) are especially vulnerable because these ecosystems are already under severe pressures due to water diversions, saltwater intrusion, and other stresses.Dry vegetation combined with high temperatures and low humidity often increases the frequency and intensity of fires. The wildfire season may start earlier in the spring and extend later into the fall.
  • Energy. Drought can strain the energy system. The generation of hydroelectricity at California dams may drop dramatically from average levels because it varies directly with streamflow. As the source of electricity production shifts to the more expensive fossil fuel (e.g., natural gas), electricity prices will likely increase. Additionally, high temperatures associated with drought may increase energy demand for cooling and air-conditioning systems.
  • Agriculture. Some farmers and water districts with “junior” water rights have seen water allocations from state and federal irrigation projects severely cut. Some growers with “senior” water rights have seen only modest shortages, if any. Farmers facing a water shortage may seek temporary water transfers from other users, increase groundwater pumping, change the types of crops they grow, deficit irrigate, or leave some lands fallow.
  • Rural Communities. Rural communities are often dependent on a single water source, usually groundwater. As groundwater levels drop, community and individual wells may go dry. Declining water supplies and ongoing water quality problems force communities to switch to bottled water, dig deeper wells, and truck in water to refill holding tanks. These actions can impose local economic hardships on those living in rural areas, many of whom are among the state’s most disadvantaged communities.
  • Urban Areas. Urban water utilities have rolled out a wide range of voluntary and mandatory water conservation programs. These include education programs, incentives to purchase more water-efficient appliances and plant water-efficient gardens, and restrictions on discretionary water uses, such as watering lawns. As a result, statewide urban water use has declined by nearly 25% from 2013 levels (see Pacific Institute’s interactive data visualization tool).
  • Revenue Losses. For most water utilities, fixed costs (e.g., debt service on past water system investments) are relatively high and variable costs (e.g., energy and chemical costs) are relatively low. Reducing water use cuts variable costs but has no impact on fixed costs (at least in the short term). As water use declines, revenue from the sale of water also declines and may not be sufficient to recover the fixed costs. In response, water utilities may enact drought surcharges or draw from reserves. While surcharges increase the water rate (i.e., the price per gallon), those using less water may actually see their bills go down. Furthermore, conservation lessens the impact of the drought on water bills by avoiding the purchase of more expensive water supplies.


How do we know when a drought is over?

Generally speaking, a third of the state’s water needs are met by the Sierra snowpack, another third by groundwater, and the rest by surface runoffs and water collected in reservoirs. Droughts incur a significant water deficit, so California needs substantial amounts of rain and snow to fall in the right places (i.e., in the mountains) and under the right conditions (i.e., as snow) to have a lasting chance of drought recovery. Replenishing aquifers takes much longer. During a drought, you can follow updates on current drought conditions and related news here.

Overall, California is becoming drier, and climate change is projected to increase the frequency, intensity, and duration of future droughts.


Californiadrought.org is a project of the Pacific Institute in Oakland, California, one of the world’s leading independent nonprofits researching and finding solutions to freshwater issues.

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