What causes drought?

A drought is a period of drier-than-normal conditions that results in water-related problems.

The amount of precipitation at a particular location varies from year to year, but over a period of years, the average amount is fairly constant. In the deserts of the Southwest, the average precipitation is less than 3 inches per year. In contrast, the average precipitation in the Northwest is more than 150 inches per year.

When little or no rain falls, soils can dry out and plants can die. When rainfall is less than normal for a period of weeks to years, streamflows decline, 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.

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What are the long-term effects of climate change?

Scientists have predicted that long-term effects of climate change will include a decrease in sea ice and an increase in permafrost thawing, an increase in heat waves and heavy precipitation, and decreased water resources in semi-arid regions. Below are some of the regional impacts of global change forecast by the Intergovernmental Panel on...

How can climate change affect natural disasters?

With increasing global surface temperatures the possibility of more droughts and increased intensity of storms will likely occur. As more water vapor is evaporated into the atmosphere it becomes fuel for more powerful storms to develop. More heat in the atmosphere and warmer ocean surface temperatures can lead to increased wind speeds in tropical...

What is the difference between global warming and climate change?

Although people tend to use these terms interchangeably, global warming is just one aspect of climate change. “Global warming” refers to the rise in global temperatures due mainly to the increasing concentrations of greenhouse gases in the atmosphere. “Climate change” refers to the increasing changes in the measures of climate over a long period...

What are some of the signs of climate change?

• Temperatures are rising world-wide due to greenhouse gases trapping more heat in the atmosphere. • Droughts are becoming longer and more extreme around the world. • Tropical storms becoming more severe due to warmer ocean water temperatures. • As temperatures rise there is less snowpack in mountain ranges and polar areas and the snow melts...

Why doesn't a drought end when it rains?

Rainfall in any form will provide some drought relief. A good analogy might be how medicine and illness relate to each other. A single dose of medicine can alleviate symptoms of illness, but it usually takes a sustained program of medication to cure an illness. Likewise, a single rainstorm will not break the drought, but it might provide temporary...

When does a drought begin and end?

The beginning of a drought is difficult to determine. Several weeks, months, or even years might pass before people know that a drought is occurring. The end of a drought can occur as gradually as it began. The first evidence of drought is usually seen in records of rainfall. Within a short period of time, the amount of moisture in soils can begin...

Where in the Nation are droughts or very low flows occurring now? How can I see these sites on a map and get to the data?

To view the USGS streamflow information on drought, see the drought map on our WaterWatch site, which shows below-normal, 7-day average streamflow compared to historical streamflow for the United States. Links to additional maps and drought data are listed on our Drought website and the U.S. Drought Portal .
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Date published: September 18, 2018

USGS Science – Leading the Way for Preparedness

Learn About USGS Hazards Science and More About National Preparedness Month: The very nature of natural hazards means that they have the potential to impact a majority of Americans every year.  USGS science provides part of the foundation for emergency preparedness whenever and wherever disaster strikes.

Date published: March 23, 2018

Plant Functional Groups Affect Ecological Drought in Semiarid Grasslands

Plant functional groups have contrasting effects on soil water availability by affecting interception, uptake, and transpiration.

Date published: July 12, 2017

New Warning System Identifies Flash Drought Quickly

Agricultural crops can wither in a flash when the days turn hot, the air dries, the rain stops and moisture evaporates quickly from the soil. A new early warning system can help alert managers and others as drought begins to happen.

Date published: June 5, 2017

New USGS Science Plan Designed to Help Plan for Drought Effects on People, Communities, and Ecosystems

The U. S. Geological Survey is poised to bring a dynamic array of science and tools to help decision-makers manage and offset effects of increased drought across the United States, according to a drought plan report released today.

Date published: October 6, 2015

Unprecedented Drought in the West

Drought has left the West parched and thirsty. Families, businesses, and farmers all need water, as do fish, wildlife, and their habitats.

Date published: September 8, 2015

Low 2015 Snowpack and River Flows Studied to Provide Insight Into Future Droughts

U.S. Geological Survey hydrologic technicians are currently taking measurements from hundreds of streams and rivers across the western United States as part of a low flow study.

Attribution: Water Resources
Date published: December 8, 2014

Data-driven Insights on the California Drought

A newly released interactive California Drought visualization website aims to provide the public with atlas-like, state-wide coverage of the drought and a timeline of its impacts on water resources.

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July 30, 2017

A Record of Change: Science and Elder Observations on the Navajo N.

A Record of Change—Science and Elder Observations on the Navajo Nation is a 25-minute documentary about collaborative studies using conventional physical sciences, combined with tribal elder observations to show that local knowledge and conventional science partnerships can effectively document ecosystem change and determine the resulting challenges to livelihoods. 

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Lake Folsom, California. Comparing drought and  non-drought conditions.
December 14, 2016

Long-term drought can seriously affect water availability

Drought in Folsom Lake, California
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The severity of California's current (2016) drought is illustrated in these images of Folsom Lake, a reservoir in Northern California located 25 miles (40 kilometers) northeast of Sacramento. The lake is formed by Folsom Dam, in the foreground, which is part of the U.S. Bureau of Reclamation

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Lake Powell half empty, 2014
November 22, 2016

Lake Powell half empty, 2014

Landsat 8 imagery of Lake Powell at 42% capacity. White bleached rock show shoreline when Lake Powell is at capacity.

Information Flows Freely, Even in a Drought
October 18, 2016

Information Flows Freely, Even in a Drought

Information Flows Freely, Even in a Drought

September 1, 2016

Drought, Drinking Water and Natural Environments

This short video is one of a series of four total shorts highlighting USGS water science in California's Delta region. The Sacramento-San Joaquin Delta is the hub of the state's water system. Water quality touches on all aspects of life. Teams of U.S. Geological Survey scientists along with their partners monitor water quality and identify sources of pollution and

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Satellite image showing Lake Mead low levels
May 23, 2016

Lake Mead Reaches Historic Low

The surface level of Lake Mead in Nevada and Arizona has fallen to a historic low as 16 years of ongoing drought in the American Southwest continue to impact the Colorado River Basin.

Image: Scientist Climbs Giant Sequoia, Sequoia National Park, CA
September 1, 2015

Scientist Climbs Giant Sequoia, Sequoia National Park, CA

A scientist from the University of California, Berkeley climbs a giant sequoia to measure its drought stress.

Image: USGS Documents 2015 Western U.S. Drought
August 26, 2015

USGS Documents 2015 Western U.S. Drought

A hydrologic technician from the USGS Idaho Water Science Center measures streamflow in Lightning Creek at Clark Fork, ID. The USGS is collecting data at hundreds of sites on rivers and streams in six western states to document the 2015 drought. USGS scientists will analyze the data to identify which rivers and streams may be most vulnerable to future droughts.