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USGS - science for a changing world

California Drought

Hydrologic science can help citizens and communities prepare for and cope with drought in two ways - through drought planning, and in helping communities make the best day-to-day management decisions while the drought is taking place.

The USGS closely monitors the effects of drought through data collection and research, and is studying the current drought in the context of long-term hydrologic, climatic, and environmental changes. These studies support successful planning and science-based decision-making by water managers who must address complex issues and competing interests in times of drought. They also and help decision-makers prepare for climate change and possible future drought.


Drought Defined

A drought is a period of drier-than-normal conditions that results in water-related problems. When rainfall is less than normal for several weeks, months, or years, the flow of streams and rivers declines, water levels in lakes and reservoirs fall, and the depth to water in wells increases. If dry weather persists and water-supply problems develop, the dry period can become a drought.

The term "drought" can have different meanings to different people, depending on how a water deficiency affects them. Droughts have been classified into different types such as:

  • meteorological drought - lack of precipitation
  • agricultural drought - lack of soil moisture, or
  • hydrologic drought -reduced streamflow or groundwater levels

It is not unusual for a given period of water deficiency to represent a more severe drought of one type than another type. For example, a prolonged dry period during the summer may substantially lower the yield of crops due to a shortage of soil moisture in the plant root zone but have little effect on groundwater storage replenished the previous spring.

Updated December 20, 2016

Drought Facts

  • On January 17, 2014 California State Governor, Jerry Brown, declared a drought state of emergency.
  • More than 33 million people in California are currently affected by drought.
  • California's response to its ongoing drought has been guided by a series of executive orders issued by Governor Brown, the most recent ordering continued, long-term water savings as drought persists.
  • The time period of Dec 2015 - Nov 2016 has been the 3rd warmest on record for California. California saw 2015 as the warmest year on record.
  • The latest National Weather Service Climate Prediction Center long-range, 1-month precipitation outlook for January 2017, issued December 15, 2016, suggests average precipitation for all of California, except for the southern fourth of the State where below average precipitation is expected.

Snowpack Status

  • Snowpack, through runoff, provides about one-third of the water used by California's cities and farms. The snowpack at the beginning of April is crucial because this is when the snowpack is normally at its peak and begins to melt into streams and reservoirs.
  • Even though parts of Northern California experienced average to slightly above average precipitation during Water Year 2016, California suffered 'Snow Drought,' which has impacted statewide water availability.
  • As of January 3, 2017, regional snowpack from automated snow sensors is 70% of normal for this date (California Department of Water Resources).
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What are the impacts of drought?

Water quality degradation, surface and groundwater level declines, land subsidence - all are impacts of drought. Understanding the impacts of drought can help mitigate drought-related issues and prepare for future dry periods.


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How does drought affect groundwater?

Groundwater provides drinking water for a large portion of the nation's population, supplies business and industries, and is used extensively for irrigation. But what happens to this resource during drought?


small graphic of a streamflow datamap

How does drought affect surface water?

Careful observation and analysis of the movement and condition of surface water is essential for understanding this resource, especially during times of drought. The California Water Science Center uses a network of over 400 streamgages to collect real-time data on surface water at locations across the state.


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How is water managed during a drought?

Water shortages during drought are not only a concern for humans, but for ecosystems in the Bay Delta and Central Valley as well.