California Drought

Science Center Objects

The USGS closely monitors the effects of drought through data collection and research. USGS science supports water managers in preparing for possible future drought by providing information that takes into account 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.


What is Drought?

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.

During times of drought, vegetation is visibly dry, stream and river flows decline, water levels in lakes and reservoirs fall, and the depth to water in wells increases. As drought persists, longer-term impacts can emerge, such as land subsidence, seawater intrusion, and damage to ecosystems. Unlike the immediate impacts of drought, however, long-term impacts can be harder to see, but more costly to manage in the future.

>> Drought Impacts 


Drought Comparisons

Because of their duration and severity in terms of both lack of rainfall and runoff, the 1928-34 drought, which lasted 7 years, and the 1987-92 drought, which lasted 6 years, are compared to the 2012-16 drought, which lasted 5 years, to assess similarities and differences.

>> Explore Historical Droughts



Runoff is an important parameter in assessing drought impact severity. The amount of runoff is dependent upon many factors including the amount, location and type of precipitation (rain or snow); rainfall rates; the amount of base flow (i.e. contribution of groundwater to streamflow); antecedent soil moisture conditions; the amount of empty surface water reservoir storage; the magnitude to which groundwater aquifers are drawn down; watershed geology and topography; the level of urbanization in the watershed; and the amount and type of landscape and cultivated plant cover.   We track both monthly and annual runoff data.

>> Runoff Data


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 more than 500 streamgages to collect real-time data on surface water at locations across the state.

>> Drought & Surface Water



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?

>> Drought & Groundwater


panorma images of Shasta Lake comparing the water level from February 3, 2014 to October 5, 2014 after 6 months of drought

Located in Shasta County, Shasta Lake is the largest manmade reservoir in California, with a capacity of 4,552,000 acre-feet. These photos, taken in February, 2014 and October, 2014, illustrate the declining water levels in the reservoir.

Shasta Lake provides abundant recreation, including boating, fishing, swimming, water skiing, camping, hunting, and houseboating. Releases from the reservoir serve to control floodwaters and store surplus winter runoff for irrigation in the Sacramento and San Joaquin Valleys, maintain navigation flows, provide flows for the conservation of fish in the Sacramento River and water for municipal and industrial use, protect the Sacramento-San Joaquin Delta from intrusion of saline ocean water, and generate hydroelectric power. (Note: Information courtesy of the U.S. Bureau of Reclamation). USGS Images by Angela Smith (top) and Cathy Munday (bottom). (Public domain.)