Drought

Droughts cause a range of impacts and are often worsened by the effects of climate change on the water cycle. A drought is a period of drier-than-normal conditions. A drought can last for days, months or years. Drought often has large impacts on the ecosystems and agriculture of affected regions, and causes harm to the local economy.

Drought is a recurring feature of the climate in most parts of the world, becoming more extreme and less predictable due to climate change. There are three kinds of drought effects, environmental, economic and social. Environmental effects include the drying of wetlands, more and larger wildfires, loss of biodiversity.

Economic impacts of drought result due to negative disruptions to agriculture and livestock farming, forestry, public water supplies, river navigation, electric power supply (by affecting hydropower systems) and impacts on human health. Social and health costs include high food costs, stress caused by failed harvests, water scarcity, etc. Drought can also lead to increased air pollution due to increased dust concentrations and wildfires.

Definition

A drought is a time when there is less water than usual. This can happen in many places and for different lengths of time, from a few days to many years. Droughts can hurt plants, animals, and people because there isn’t enough water to meet everyone’s needs. Different groups and scientists may describe droughts in slightly different ways, but they all agree that droughts are periods of drier conditions that can cause problems.

Categories

There are three main types of drought, depending on where the water shortage happens:

1. Meteorological drought happens when there is less rain than usual for a long time. This type of drought usually comes first and can lead to the other types.
2. Hydrological drought occurs when water in lakes, rivers, and underground stores runs low. This type of drought develops slowly because it involves water that we use but don't always replace.
3. Agricultural or ecological drought affects plants and nature when there isn't enough water for crops or the environment, even if the rain amount hasn't changed.

All these droughts have different causes but can hurt farms, nature, and local communities in similar ways.

Indices and monitoring

Several tools help us measure and watch for droughts. These tools use information about rain, temperature, and plants to see how dry things are getting. Some important tools include:

• Palmer drought index: This tool looks at rain and temperature to study how dry a place is.
• Keetch-Byram Drought Index: This one uses rain, temperature, and other weather details.
• Standardized precipitation index (SPI): This is a simple way to watch for droughts using rain data. The World Meteorological Organization suggests using this tool.
• Standardized Precipitation Evapotranspiration Index: This tool looks at both rain and how much water the air takes in, which also affects drought.

These tools help us understand where and how bad droughts might be, which is important for keeping places safe and ready for dry times. Using more than one tool gives a better picture, especially in areas where there isn’t a lot of weather data.

Causes

General precipitation deficiency

See also: Precipitation

Rain can fall in different ways, like heavy downpours or lighter, longer rains. When there isn’t enough rain over time, it can lead to a drought. Droughts often happen in places that don’t normally get much rain. Things like strong sunlight, high pressure, and certain wind patterns can stop rain from falling, making droughts worse.

Dry season

See also: Dry season

In warm areas of the world, there are times with very little rain called dry seasons. During these times, rivers and water holes can dry up, making life hard for animals like zebras, elephants, and wildebeest who need to move to find water. Plants also suffer without enough water, and this can lead to more wildfires.

El Niño–Southern Oscillation (ENSO)

Further information: El Niño–Southern Oscillation

The El Niño–Southern Oscillation can affect weather patterns and sometimes make droughts worse. During La Niña, places like California and the Southwestern United States can get drier and hotter. During El Niño, areas such as the Amazon River Basin, Colombia, and Central America can also become drier. These changes in weather can affect rain patterns and make droughts more likely in different parts of the world.

Climate change

See also: Effects of climate change on the water cycle and Effects of climate change on agriculture

Warmer temperatures and changes in climate have led to more frequent and severe droughts around the world. Human activities, like how we use land and manage water, also make droughts worse. Scientists have noticed that warmer weather makes soil drier and plants struggle more for water, which can lead to agricultural and ecological problems.

Vegetation changes, erosion and human activities

See also: Aeolian processes

Human actions such as farming, cutting down trees, and improper irrigation can harm the land’s ability to hold water, making droughts worse. In dry areas, wind can blow away soil and plants, which also makes the land drier. When plants grow back in certain ways, it can sometimes change how the soil holds water, affecting drought conditions.

Impacts

Drought is a serious natural event that can greatly affect the environment, the economy, water supplies, farming, and society everywhere.

Droughts can harm the environment by lowering water levels, increasing pollution, causing more wildfires, and damaging wildlife habitats. They can also hurt the economy by reducing farming output, raising food prices, and lowering energy production. For example, from 1991 to 2023, droughts caused about USD 278 billion in damage.

Farming is especially affected by droughts. Without enough water, crops can fail, and animals can suffer. Plants grow poorly because they cannot take in nutrients or make food properly. This leads to smaller plants and lower yields.

For people, droughts can cause serious problems like food shortages, hunger, and poverty. They can also lead to health issues from heat and dirty water. Some people may have to leave their homes because of these problems. Droughts can also cause conflicts over limited water and food resources.

Droughts can also damage fertile soil by increasing wind erosion, especially in dry areas. This can wash away valuable topsoil and make farming harder. Farmers often plant trees and bushes to protect their soil from wind.

Regions particularly affected

Main article: List of droughts

Amazon basin

See also: Amazon Rainforest § Impact of early 21st century Amazon droughts

In 2005, parts of the Amazon basin had a very dry spell—the worst in over 100 years. Scientists worry that if droughts keep happening, the rainforest might change into a dry, open landscape, which could affect the whole world's climate.

Australia

From 1997 to 2009, Australia had a long dry spell called the Millennium Drought. This caused big water problems, so new water treatment plants were built. Much of Australia is dry land, and some experts think that long ago, people may have changed the weather patterns by regularly setting fires. In 2008, experts warned that a major river area might face serious problems if it didn’t get more rain soon. The drought ended in 2010.

East Africa

East Africa includes countries like Ethiopia, Kenya, and Uganda. The weather there can change a lot, with dry periods and wet periods. Long droughts have sometimes led to not enough food, like in 1984–85 and again more recently from 2020 to 2023. Some areas also faced big floods during this time. The changing weather patterns make it hard for people to plan for the future.

Himalayan river basins

About 2.4 billion people live where rivers flow from the Himalayas. Countries like India, China, Pakistan, Bangladesh, Nepal, and Myanmar may see both floods and droughts in the future. Droughts could affect the Ganges River, which gives water to over 500 million people for drinking and farming. In 2025, the UN warned that melting glaciers might threaten the water and food supply for billions of people around the world.

North America

The west coast of North America relies on glaciers in mountain ranges like the Rocky Mountains and Sierra Nevada for water. These areas could also be affected by changes in weather patterns.

By country or region

Different places around the world have faced serious droughts. Some examples include:

• Droughts and famines in Russia and USSR
• Droughts in California
• Droughts in the Sahel
• 2021 Madagascar food crisis
• 2010 China drought and dust storms
• Cape Town water crisis in 2015–2018

Protection, mitigation and relief

See also: Water scarcity, Water supply, and Water security

When there is not enough rain, farmers can still protect their crops in several ways. They can use water from reservoirs made by building dams, or try to bring more rain through a process called cloud seeding. Planning which crops to plant each year, called crop rotation, helps keep the soil healthy and lets farmers choose crops that need less water in dry years. In very dry places, people sometimes build canals to move water from rivers to fields for irrigation.

When water is hard to find, people can look for other sources. This might include using water that has already been used, called wastewater reuse, collecting rain in special tanks known as rainwater harvesting, or even turning salt water into fresh water through desalination.

History

See also: List of droughts

Throughout history, people have often seen droughts as big problems because they affect food and many parts of life. Droughts are some of the oldest weather events we know about, mentioned in old stories like the Epic of Gilgamesh and connected to the Biblical tale of Joseph in ancient Egypt. Scientists can now explain droughts using nature and how humans affect the world. In many places, people still think droughts might be caused by invisible forces or as a message from above.

In the past, people performed special ceremonies to try to bring rain, ranging from dances to other practices. Some of these old ways are now just stories, while others are still remembered. In places where science isn’t well known, beliefs about drought can still shape how people understand and respond to these tough times.

Some famous droughts in history include:

• The 4.2-kiloyear event, a big dry time in Africa and Asia that may have affected old empires.
• The longest drought ever recorded began 400 years ago in the Atacama Desert in Chile and continues today.
• Drought may have played a role in changes for ancient cultures like the Classic Maya collapse.
• The year 1540 in Central Europe was extremely dry, with almost no rain for eleven months.
• Droughts in the past have sometimes led to very hard times for many people, but these stories are complex and hard to understand fully.