USGS Groundwater Information
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Groundwater and Drought
Groundwater is among the Nation's most important natural resources. It provides half our drinking water and is essential to the vitality of agriculture and industry, as well as to the health of rivers, wetlands, and estuaries throughout the country. Droughts can significantly impact the Nation's groundwater resources while the drought is occurring and for some time afterward. Understanding groundwater, surface water, and the integrated nature of the hydrologic system enables resource managers and policy makers to better prepare for and respond to drought. The USGS provides groundwater data and information that resource managers and policy makers can use to prepare for and respond to drought.
What is Drought?
Sample graph of daily groundwater level data. Daily groundwater levels (bottom line) for the period shown are below the historical daily median (top line). (View the latest statistics for this well.)
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:
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.
What is a groundwater drought?
A groundwater drought typically refers to a period of decreased groundwater levels that results in water-related problems. The amount of groundwater decline that would be considered a drought varies regionally and locally due to differences in groundwater conditions and groundwater needs for humans and the environment.
How is groundwater important during drought?
Groundwater is important during all hydrologic droughts:
Pool and dry river bed along the Ipswich River, Reading, Massachusetts, September 2005. Groundwater withdrawals for primarily domestic and commercial uses in the Ipswich River Basin in eastern Massachusetts have caused substantial depletions of streamflow. Credit: USGS/Photograph by David Armstrong (Source: Circular 1376)
A 1942 photograph (left photograph) of a reach of the Santa Cruz River south of Tucson, Arizona, shows stands of mesquite and cottonwood trees along the river. A replicate photograph of the same site in 1989 (right photograph) shows that the riparian trees have largely disappeared. Data from nearby wells indicate that the groundwater levels declined more than 100 feet due to pumping, and this pumping appears to be the principal reason for the decrease in vegetation. Credit: USGS/Photograph by Robert H. Webb (Source: Circular 1186)
For more background on drought:
For additional USGS background on drought, see: