essay about different types of droughts

• What Are The Different Types Of Drought?

A drought usually refers to a period of lower-than-average precipitation leading to sustained periods of low water supply and the resultant negative effects of such an event. Droughts often lead to famines and result in the deaths of humans, animals, and plants. A list of the different types of droughts and their causes is listed below.

Meteorological/Climatological Drought

Droughts caused due to meteorological factors are most common in nature and usually precede other types of droughts. Such an event is caused by a prolonged period of low precipitation. Dry weather patterns dominate the area experiencing a climatological drought. The severity of such droughts depends on the magnitude of the shortfall of precipitation, as well as the duration of the shortfall event.

Agricultural Drought

An agricultural drought occurs when crop growth in an area is adversely affected due to drought. Often, meteorological droughts lead to agricultural droughts. Low levels of precipitation over a sustained period of time can lead to crop failure. However, such droughts can also occur in the absence of changes in precipitation levels. Poor agricultural practices can occasionally lead to changes in soil conditions or soil erosion that will decrease the amount of water available to crops for proper growth. Agricultural droughts are more common in non-irrigated agricultural areas where a plant’s source of water is largely dependent on prevailing weather conditions.

Hydrological Drought

Hydrological droughts occur when a water supply becomes scarce due to lower water levels in water bodies likes lakes, rivers, and reservoirs. Often, meteorological droughts precede hydrological droughts since low levels of rainfall and high temperatures may cause water bodies to dry up. However, changes in weather conditions are not always the cause of hydrological droughts. For example, when a country or region diverts a vital water source towards its own territory, leaving a neighboring country or region dry, it can lead to a drought in the latter area. Kazakhstan suffered from drought-like conditions under Soviet rule when water from the Aral Sea was diverted to other nations. The country was thus offered a large sum of money by the World Bank to overcome the resulting losses.

Socioeconomic Drought

A socioeconomic drought occurs when the demand for an economic good is greater than its supply due to a water deficit created by shortfalls in precipitation and other weather-related adverse changes. Many goods like food grains, fodder, fish, and hydroelectricity need an adequate water supply for sufficient production. For example, Uruguay suffered a downfall in hydroelectric power production from 1988 to 1999. A meteorological drought in the country led to a deficit of water in the streams generating hydroelectric power. Thus, the government had to resort to the more expensive petroleum as a source of fuel and implement strict energy conservation measures.

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Understanding Droughts

Drought is an extended period of unusually dry weather when there is not enough rain.

Biology, Ecology, Earth Science, Meteorology, Geography, Human Geography, Physical Geography, Social Studies, U.S. History, World History, Geology

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Drought  is an extended period of unusually dry  weather  when there is not enough rain. The lack of  precipitation  can cause a variety of problems for local communities, including damage to  crops and a shortage of drinking water. These effects can lead to devastating  economic  and social disasters, such as  famine ,  forced migration  away from drought -stricken areas, and  conflict  over remaining  resources .

Because the full effects of a drought can develop slowly over time, impacts can be underestimated. However, drought can have  drastic  and long-term effects on  vegetation , animals, and people. Since 1900, more than 11 million people have died and more than 2 billion people have been affected by drought . Drought is also one of the costliest weather -related disasters. Since 2014 California has lost at least 2 billion-dollars a year, due to drought .

Defining Drought

Drought is a complicated  phenomenon , and can be hard to define. One difficulty is that drought means different things in different regions. A drought is defined depending on the average amount of precipitation that an area is accustomed to receiving.

For example, in Atlanta, Georgia, the average rainfall is about 127 centimeters (50 inches) a year. If  significantly less rain falls, there may be water shortages and a drought may be declared. However, some arid regions, such as the  deserts of the American Southwest, may receive less than about 25 centimeters (10 inches) of rainfall in a non- drought year. A drought in Atlanta could be a very wet period in Phoenix, Arizona!

Determining the start of a drought can be tricky. Unlike many  natural hazards that bring about sudden and dramatic results—such as  earthquakes ,  tornadoes , and  hurricanes —the onset of a drought can be gradual and subtle. It can take weeks, months, or even years for the full effects of long-term  inadequate  rainfall to become apparent.

The end of a drought can also be difficult to determine. While a single rain storm will provide short-term relief from a drought , it might take weeks or months before levels of precipitation return to normal. The start and end of a drought are often only clear in hindsight .

Causes of Drought

Most droughts occur when regular weather patterns are interrupted, causing  disruption to the  water cycle . Changes in  atmospheric circulation  patterns can cause storm tracks to be  stalled for months or years. This disruption can dramatically impact amounts of precipitation that a region normally receives. Changes in wind patterns can also be disruptive to how moisture is absorbed in various regions.

Scientists have found a link between certain  climate  patterns and drought . El Niño is a weather event where the surface water in the Pacific Ocean along the central South American coast rises in temperature. These warmer waters alter storm patterns and are associated with droughts in Indonesia, Australia, and northeastern South America. El Nino events keep climate scientists guessing, by occurring every two to seven years.

La Niña is the counterpart to El Niño , when the surface water in the Pacific Ocean along the coast of South America decreases in temperature. The cooler waters affect storm patterns by contributing to drier-than-normal conditions in parts of North and South America. El Niño and La Niña both usually last about a year. The effects of La Niña on weather patterns are often more  complex  than El Niño . Two of the most devastating droughts in the history of the United States—the 1930s  Dust Bowl  and the 1988 drought in the Midwest—are associated with the effects of La Niña.

There is still a lot of debate about the connection between drought and  global warming , the current period of  climate change . A 2013 NASA study predicts warmer worldwide temperatures will mean increased rainfall in some parts of the world and decreased rainfall in others, leading to both more flooding and more droughts worldwide. Other scientists question the prediction that there will be more droughts and believe global warming will create a wetter climate around the world.

Impacts of Drought

Trees and other plants have adapted to withstand the effects of drought through various survival methods. Some plants (such as grasses) will slow their growth or turn brown to conserve water. Trees can drop their leaves earlier in the season to prevent losing water through the leaf surface. However, if drought conditions persist, much vegetation will die.

Certain plants have adapted so they can withstand long periods without water. Yuccas, for instance, have deep  root systems that can seek out water with incredible efficiency. Cacti have spiny, hairy spines, spikes, or leaves that limit how much water they lose to  evaporation . Mosses can withstand complete  dehydration . Juniper trees can self- prune  by steering water only to ward the branches required for survival. Other plants only grow when there is enough water to support them. In periods of drought , their seeds can survive under the  soil for years until conditions are favorable again.

However, many organisms cannot adapt to drought conditions, and the environmental effects of extended, unusual periods of low precipitation can be  severe . Negative impacts include damage to  habitats , loss of  biodiversity , soil   erosion , and an increased risk from  wildfires . During the U.S. drought of 1988, rainfall in many states was 50 to 85 percent below normal. Summer thunderstorms produced  lightning  without rain and  ignited fires in dry trees. In Yellowstone National Park 36 percent of the park was destroyed by fire.

Drought can also create significant economic and social problems. The lack of rain can result in crop loss, a decrease in land prices, and  unemployment  due to declines in production. As water levels in rivers and lakes fall, water-supply problems can develop. These can bring about other social problems. Many of these problems are health-related, such as lack of water, poor  nutrition , and famine . Other problems include conflicts over water usage and food, and forced migration away from drought -stricken areas.

While drought is a naturally occurring part of the weather cycle and cannot be prevented, human activity can influence the effects that drought has on a region. Many modern agricultural practices may make land more  vulnerable to drought . While new  irrigation  techniques have increased the amount of land that can be used for farming, they have also increased  farmers ’ dependence on water.

Traditional agricultural techniques allow land to “rest” by rotating crops each season and alternating areas where  livestock graze . Now, with many areas in the world struggling with overpopulation and a shortage of farmland, there is often not enough  arable  land to support  sustainable practices. Over-farming and  overgrazing  can lead to soil being  compacted and unable to hold water. As the soil becomes drier, it is vulnerable to erosion . This process can lead to  fertile  land becoming desert -like, a process known as  desertification . The desertification of the  Sahel  in North Africa is partly blamed on a prolonged drought whose effects were intensified by farming practices that result in overgrazing .

Increased drought conditions in Kenya have been attributed to  deforestation and other human activities. Trees help bring precipitation into the ground and prevent soil erosion . But in 2009, it was reported that one-quarter of a protected forest reserve had been cleared for farming and  logging , leading to drought conditions affecting 10 million people around the country.

Historical Droughts

Scientists often study historical droughts to put modern-day droughts in perspective. Since our  data  from  thermometers and  rain gauges only goes back about 100 to 150 years, scientists must research  paleoclimatology , the study of the atmosphere of prehistoric Earth. Scientists gather paleoclimatic data from  tree rings ,  sediments found in lakes and oceans,  ice cores , and archaeological  features and  artifacts . This allows scientists to extend their understanding of weather patterns for millions of years in the past.

Analyzing paleoclimatic data shows that severe and extended droughts are an  inevitable  part of natural climate cycles. North America has experienced a number of long-lasting droughts with significant effects. It is thought that droughts brought about the decline of the  Ancestral Puebloans  in the Southwest during the 13th century, and the central and Lower  Mississippian societies in the 14th to 16th centuries.

In South America, massive migration out of the once-fertile Atacama Desert 9,500 years ago can be explained by the onset of extreme drought.

In Africa, the Sahel region experienced a dry period from 1400 to 1750 that radically altered the  landscape . The water level in Lake Bosumtwi, Ghana, for instance, fell so low that an entire forest grew on the lake’s edges. Today, visitors can still see the tops of trees growing out of the lake—where the water is now more than 15 meters (50 feet) deep.

What scientists have learned by looking at Earth’s drought history is that periods of severe drought are a regular part of nature’s cycle. As devastating as droughts in the last century have been, they are considered relatively minor compared to the severity of earlier droughts that have lasted more than a century.

Major Droughts in the Past Century

The Dust Bowl of the 1930s is probably the most well-known drought experienced by the U.S. By 1934, 80 percent of the U.S. was struggling with moderate-to- severe drought conditions. The drought lasted nearly a decade and had devastating effects on crop production in the  Great Plains . The combination of lack of rain, high temperatures, and strong winds affected at least 50 million acres of land. Massive clouds of dust and sand formed as unusually strong winds lifted the dry soil into the air. These clouds could block out the sun for days, giving the period the name “ dust bowl .” In 1934, one dust cloud infamously traveled 2,414 kilometers (1,500 miles), from the Great Plains to the eastern U.S.

Mass migration was an indirect effect of the Dust Bowl . Farmers and their families were forced to migrate to other areas in search of work, and by 1940, 2.5 million people had fled the Great Plains . Of those, 200,000 moved to California. The influx of migrants into existing economies already strained by the Great Depression led to a rise in conflict , unemployment , and  poverty .

In the 1950s, severe drought returned to the Great Plains and southwestern United States, affecting half of the continental U.S. Low rainfall and high temperatures caused the production of crops in some areas to drop nearly 50 percent. Hay became too expensive for ranchers, and they had to feed their cattle prickly pear cactus and molasses to keep them alive. By the end of the five-year drought in 1957, 244 of Texas’ 254 counties had been declared  federal   drought disaster areas .

In the late 1980s, the U.S. experienced one of the costliest drought in its history. The three-year spell of high temperatures and low rainfall ruined roughly $15 billion of crops in the  Corn Belt . The total of all the losses in energy, water,  ecosystems , and  agriculture  is estimated at $39 billion. Federal assistance programs were able to help many farmers , but a longer-lasting drought would make it more difficult for the government to provide nationwide aid.

Droughts continue to affect the U.S. Texas has been suffering from drought since 2010, with 2011 ranking as the driest year in the state’s history. A September 2012  National Geographic  magazine article called Texas “The New Dust Bowl.” By 2013, 99 percent of the state was dealing with drought.

Australia is also a frequent victim of drought . The last decade has been especially severe , earning it the name The Big Dry or The Millennium Drought . Much of the country was placed under water restrictions, wildfires spread in the dry weather , and the water level in some  dams fell to 25 percent. In 2007, 65 percent of viable land in Australia was declared to be in a drought . The drought was officially declared over in April 2012.

Droughts that occur in the  developing world  can cause even greater devastation. The Sahel region in Africa, which includes eight countries, endured a series of droughts in the 1970s and 1980s where annual rainfall dropped by about 40 percent. In the early 1970s, more than 100,000 people died and millions of people were forced to migrate. Conditions continue to be critical in the area due to drought , overpopulation, failing crops , and high food prices. Drought emergencies for the region have been declared four times since 2000.

The  Horn of Africa , which includes the countries of Ethiopia, Somalia, Eritrea, and Djibouti, is particularly vulnerable to droughts . Because almost 80 percent of the population is rural and depends on agriculture for food and income, famine often accompanies drought .

Struggles for the region’s limited, remaining resources can lead to conflict and war. In 1984 and 1985, the Horn of Africa suffered one of the worst droughts of the 20th century. The U.N. estimates that in Ethiopia alone, 1 million people died, 1.5 million livestock died, and 8.7 million people were affected by the drought—including being hospitalized, forced to migrate, or forced to change professions. In Sudan, 1 million people died, at least 7 million livestock died, and 7.8 million people were affected.

The cycle of drought-famine-conflict has persisted in the region, with drought conditions returning every few years since 2000. In 2006, drought affected 11 million people across the Horn of Africa, and the resulting crisis killed between 50,000 and 100,000 people and affected more than 13 million.

Forecasting and Measuring Drought

Even though scientists are unable to predict how long a drought will last or how severe it will be, early warning systems and  monitoring tools can  minimize  some of drought ’s damaging impacts. There are a number of tools used to monitor drought across the U.S. Due to the limitations of each system, data from different sources are often compiled to create a more comprehensive  forecast .

The Palmer Drought Severity Index (PDSI), developed in 1965 by the  National Weather Service , is the most commonly used drought monitor . It is a complex measurement system and an effective way to forecast long-term drought . Its limitations are that it does not provide early warnings for drought and is not as accurate for use in mountainous areas because it does not account for snow (only rain) as precipitation . The PDSI is often used by the U.S. Department of Agriculture to determine when to begin providing drought relief.

Information from the Standardized Precipitation Index (SPI) is often used to supplement the PDSI data . The SPI, developed in 1993, is less complex than the PDSI and only measures precipitation —not evaporation or water  runoff . Many scientists prefer using the SPI because the time period being analyzed can easily be  customized . The SPI can also identify droughts many months earlier than the PDSI. The National Drought Mitigation Center uses the SPI to monitor drought conditions around the U.S.

The U.S. Drought Monitor , started in 1999, is a joint effort between three U.S. government agencies—the Department of Agriculture , the Department of Commerce, and the National Oceanic and Atmospheric Administration (NOAA). The Monitor   synthesizes data from  academic  and federal scientists into a weekly map indicating levels of dryness around the country. It is designed to be a blend of science and art that can be used as a general summary of drought conditions around the country. It is not meant to be used as a drought predictor or for detailed information about specific areas.

The Famine Early Warning System Network (FEWS NET) monitors satellite data of crops and rainfall across Africa and some parts of Central America, the Middle East , and Central Asia. Analysis of the data allows for early intervention to try to prevent drought -induced famine .

Preparing for Drought

People and governments need to adopt new practices and policies to prepare as much as possible for inevitable future droughts . Emergency spending once a crisis has begun is less effective than money spent in preparation. The  Federal Emergency Management Agency (FEMA)  estimates that every $1 spent in planning for a natural hazard will save $4 in the long term.

Many areas are extremely vulnerable to drought as people continue to be dependent on a steady supply of water. The U.S. Department of Agriculture recommends a series of  conservation  practices to help farmers prepare for drought . Some preventative measures include in stalling an  efficient   irrigation system that reduces the amount of water lost to evaporation , storing water in ditches along fields, regularly monitoring soil moisture, planting crops that are more drought -resistant, and rotating crops to allow water in the soil to increase.

In  urban areas , many cities are promoting water conservation by addressing water usage habits. Some enforce water restrictions, such as limiting days when lawns and plants can be watered, and offering free high-efficiency toilets and kitchen faucets.

Some drought-ravaged cities are taking even more extreme measures to prepare for future droughts. In Australia, the city of Perth is planning for a massive wastewater -recycling program that will eventually provide up to a quarter of the city’s water demands by 2060. Perth has been dealing with a decline in rainfall since the mid 1970s. The city, which is on the edge of a huge desert, is also struggling with its history of over-consumption of water. Water-hungry traditions such as planting large, lush lawns and parks will need to be addressed through conservation measures.

Drought in the USA In August 2012, drought conditions extended over 70 percent of the United States. Counties in 33 states were designated “disaster counties” by the government. In the beginning of 2013, drought still affected more than 60 percent of the country.

Dust Bowl John Steinbeck’s 1939 novel The Grapes of Wrath describes the Dust Bowl drought of the 1930s: “Every moving thing lifted the dust into the air: a walking man lifted a thin layer as high as his waist, and a wagon lifted the dust as high as the fence tops, and an automobile boiled a cloud behind it. The dust was long in setting back again.”

Yunnan Drought

The ongoing drought in Yunnan Province, China, has forced some families to transport water from more than 10 kilometers (6 miles) away.

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Related Resources

Not all droughts are the same: here’s what’s different about them

Visiting Adjunct Professor, University of the Witwatersrand

Disclosure statement

Mike Muller has received funding from the Water Research Commission and the African Development Bank for research and advisory work related to the subject matter of this article. He also advises a variety of organisations on water related matters including national, provincial and local government, and business organisations including BUSA, AgriSA and SAICA.

University of the Witwatersrand provides support as a hosting partner of The Conversation AFRICA.

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There’s growing concern in South Africa about what’s being portrayed as “ a national drought disaster ”. There have been anxious suggestions that drought could see many cities and towns facing their “ Day Zero ”. This happened during the water crisis in Cape Town as fears mounted that the taps would run dry.

Concerns were reinforced when it was announced that the tunnels that bring water from the Lesotho Highlands Water Scheme to the country’s economic hub, Gauteng, would be shut for a few months.

From a technical perspective, the threat has been exaggerated. In summer rainfall areas, there has been a slow start to the rainy season. And while dam levels are lower than they were last year, they’re not yet at critical levels. An analysis of the critical Integrated Vaal River System found that there was no need for water restrictions this summer. The system supplies Gauteng and the surrounds, including large users such as Sasol, an integrated energy and chemical company, and many of the power stations that belong to the country’s electricity public utility, Eskom.

The panicked reaction suggests though that many people don’t fully understand South Africa’s climate, or how it affects the way the country’s water supply systems work. In particular, there’s limited recognition of the different types of drought and how they affect different sectors of society.

For example, dry periods can devastate agriculture without necessarily affecting water supplies to cities and industries. Plants in fields and livestock grazing on natural pasture depend on moisture in the top layers of the soil. Cities and towns either have large reserves of water in dams or tap it from aquifers, which are effectively underground reservoirs.

It would be wrong to suggest that there are no drought problems in the country at present. Parts of the Northern , Western and Eastern Cape are officially in drought conditions. This means that officials acknowledge that the prolonged dry conditions are now seriously threatening farming activities. And many farmers are battling to stay in business.

But across South Africa’s 1.2 million sq kilometres, there are also areas where rainfall has been well below average for a year or more.

Weather patterns

The South African Weather Service produces rainfall maps, which show this variation. The map for the 2015–2016 season shows a mixture of very dry and very wet areas, sometimes quite close to each other.

The 2018-2019 season showed a different pattern with the western half of the country much drier than the eastern, and parts of the Northern Cape receiving less than 25% of their average rainfall.

Climate scientists, hydrologists and disaster management specialists have traditionally distinguished between three different kinds of drought:

A meteorological drought occurs when rainfall is less than average over a significant period, often a month.

An agricultural drought is considered to be taking place when a lack of rainfall leads to a decline in soil moisture affecting pastures and rain-fed crops. A good way to visualise an agricultural drought is to show rainfall records and vegetation conditions on maps.

A hydrological drought occurs when a meteorological drought significantly reduces the availability of water resources in rivers, lakes and underground. Currently, except in a few places (Northern, Eastern and Western Cape and pockets of Limpopo) there is not yet a hydrological drought in South Africa.

So the immediate drought problems that need to addressed are those affecting the country’s farmers, not those affecting municipal water supply. Although there are places where domestic water supply is problematic, only a few of these are due to drought and most are due to mismanagement and poor planning .

A meteorological drought is usually simply an alert to warn farmers and water managers that they need to be ready to act, in case it continues.

Responses to an agricultural drought depend on the kind of farming that is undertaken. Livestock farmers are advised either to reduce their herds or buy additional feed, to compensate for lost grazing. Dry land crop farmers may delay planting or, if they are brave, space their crops more widely to give each plant a better chance of getting enough water. They may also take out insurance against crop failure due to drought.

When a hydrological drought occurs, water managers responsible for supplying towns and cities need to implement previously prepared plans to restrict water use as storage levels decline, since this determines how much water can continue to be reliably be supplied.

Going forward

A group of international academics think that we should change the way we think about droughts. They point out that human action has substantially changed the way that the water cycle works by damming and diverting rivers and pumping water from underground. They argue that:

We need to acknowledge that human influence is as integral to drought as natural climate variability.

For the scientists this means that they must change the way they look at drought:

Drought research should no longer view water availability as a solely natural, climate imposed phenomenon and water use as a purely socio-economic phenomenon, and instead more carefully consider the multiple interactions between both.

From this perspective, Cape Town’s “Day Zero” would fall into a new category: a “human induced drought”. And, if the citizens of Gauteng don’t heed the warning to reduce water use to what can be provided by the Integrated Vaal River System over the next five or six years, they should not be surprised if they too suffer a “human induced drought”.

The World Water Council has put it succinctly:

The crisis is not about having too little water to satisfy our needs. It is a crisis of managing water so badly that billions of people – and the environment – suffer.

This article is the third and final in a series on South Africa’s water challenges.

Read more: Panic over water in South Africa's economic hub is misplaced

Read more: South Africa’s real water crisis: not understanding what's needed

• Agriculture
• Climate change
• Weather forecasting
• Food production
• South Africa
• Peacebuilding
• Food shortages
• Lesotho Highlands
• Municipal governance
• South Africa water challenges

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Home — Essay Samples — Environment — Deforestation — Drought: Types, Impacts and Preventive Measures

Drought: Types, Impacts and Preventive Measures

• Categories: Deforestation

About this sample

Words: 1319 |

Published: Oct 22, 2018

Words: 1319 | Pages: 3 | 7 min read

• Meteorological drought: it simply implies rainfall deficiency where the precipitation is reduced by more than 25%from normals in any given area. These are region specific since deficiency of precipitation is highly variable from region to region.
• Hydrological drought: these are associated with the deficiency of water on surface or subsurface due to a shortfall in precipitation. Although all droughts have their origination from a deficiency in precipitation, hydrological drought is mainly concerned about how this deficiency affects components of the hydrological system such as soil moisture, stream flow, groundwater and reservoir levels etc.
• Agricultural drought: this links various characteristics of meteorological or hydrological drought to agricultural impacts, focusing on precipitation shortages, differences between actual potential evapotranspiration, soil, soil water deficits, and reduced groundwater or reservoir levels. Plant water demand depends on prevailing weather conditions, biological characteristics of the specific plant, and its stage of growth and the physical and biological properties of the soil.
• Socio-economic drought: it is associated with the demand and supply aspect of economic goods together with elements of meteorological, hydrological and agricultural drought. This type of drought mainly occurs when there the demand for an economic good exceeds its supply due to a weather-related shortfall in water supply
• Dams/reservoirs and wetlands to store water;
• Improvement in agriculture through modifying cropping patterns ;
• Watershed management and introducing drought-resistant varieties of crops ;
• Water rationing ;
• Management of rangeland with the improvement of grazing patterns;
• Cattle management introduction of feed and protection of shrubs and trees.
• Proper selection of crop for drought-affected areas ;
• Development of water resource system with improved irrigation;
• Leveling, soil-conservation techniques development of improved storage facilities;
• Reducing deforestation and fire-wood cutting in the affected areas protection of surface water from evaporation and introduction;
• Alternative land-use models for water sustainability of drip irrigation system;
• Checking of migration and providing alternate employment;
• Animal husbandry activities can help in mitigation with use of improved;
• Education and training to the people and scientific methods;
• Participatory community programmes.

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Drought Basics

PBS, WGBH Educational Foundation

This PBS Learning Media activity addresses drought basics, including its causes and impacts and ways to assess it, by using media from NOAA and NASA. It defines the types of drought, the impacts, monitoring, and responses to drought. Use this resource to stimulate thinking and questions on the complexity of drought and to identify some variables used in defining drought.

Notes from our reviewers

The CLEAN collection is hand-picked and rigorously reviewed for scientific accuracy and classroom effectiveness. Read what our review team had to say about this resource below or learn more about how CLEAN reviews teaching materials .

• Teaching Tips Material includes Teaching Tips and prepared Discussion Questions. Suggested Teaching Tips are sparse, but the material would be a good supplement for a prepared drought lesson. Slideshow has 15 slides with roughly two paragraphs of text per slide. If students are interested in more information about a climate science topic they can explore other resources directly from the homepage.
• About the Science In this slideshow students learn about five types of drought, their causes, and impacts on the continental USA. Students learn the difference between drought, aridity, and water shortage through text, real-life examples, and figures. Slides include graphs and animations from cited sources that include NASA, USDA, NOAA, and USDMâhowever there is not a link to the original material. Comments from expert scientist: This is a great holistic overview of drought types, causes and impacts. The resource introduces ENSO and includes several scientific plots/visualizations from scientific models but I noticed a few of the images did not include a source.
• About the Pedagogy This resource could be used as a whole group presentation/lecture or assigned as an independent study. The format is good for visual learners, due to its balance of text and images. However, students cannot interact directly with the graphs/figures/maps on each slide beyond clicking to step through the slides and hit play on the embedded videos. This presentation is more powerful when put with other resources in the multimedia series and provides good background for student investigations. Great introduction to drought with natural drivers and cascading efforts. The activity does not list any prerequisite knowledge or skill. Correlations to standards indicated on the website are elaborate and may not accurately reflect standards addressed in the activity.
• Technical Details/Ease of Use Slideshow is easy to follow and use while being free of distractions. Integrated share to Google Classrooms button. Also can be assigned through Remind, social media platforms, or with the PBS LearningMedia Lesson Builder Tool.

A  natural disaster  is a major adverse event. Disaster results from natural processes of the Earth. Droughts are one of them. Drought is basically the unusual dryness of the soil.

                                                                                                      Droughts

Introduction to Droughts

Drought is shortly the unusual dryness of soil due to the levels of rainfall. Drought occurs when rainfall is significantly below average over a prolonged period. It is an event of shortages in the water supply, surface water, or groundwater. A drought can last for years, months or days.

Shortage of water, Dry and hot winds, rise in temperature, and consequent evaporation of moisture from the ground contribute to conditions of drought. Droughts also result in crop failure too. Droughts have a major impact on the  ecosystem  and agriculture of the affected regions. Also, droughts harm the local economy of the region. Droughts are considered a natural disaster as it disturbs our whole ecosystem.

Drought is considered as the recurring feature of the climate in most parts of the world. These days regular droughts have become more extreme and more unpredictable because of climatic changes. Also, studies based on dendrochronology, confirm that the drought-affected by global warming goes back to 1900.

Millennium Drought in Australia (1997–2009) is a well-known historical drought. The drought led to a water supply crisis across the country. As a result of it, many desalination plants were built for the first time. These plants are meant for the process of removing salt from seawater. The State of Texas in 2011, lived under a drought emergency declaration for the whole year. The state suffered severe economic losses. If ant time drought persists, the conditions surrounding the region gradually worsen and its impact on the local population gradually increases day by day.

Types of Droughts

Meteorological drought.

This type of drought occurs when there is a prolonged time with less than average rainfall. Meteorological drought usually paves the way for other kinds of drought.

Agricultural Drough t

This type of drought affects crop production or the ecology of the range. The conditions of drought can arise independently due to any change in precipitation levels, irrigation, or soil conditions.  Erosion occurs because of poorly planned agricultural attempts. This causes a shortfall in water available to the crops causes drought. However, the traditional drought occurs due to an extended period of below-average rainfall.

Hydrological Drought

This type of drought occurs when the water reserves available to us fall below a significant threshold. These sources are that are aquifers, lakes and reservoirs fall. Hydrological drought tends to show up more slowly.

This slow pace of drought is because it involves stored water that is used but not replenished from sources. Like an agricultural drought, this can be triggered by more than just a loss of rainfall. For example, around 2007 Kazakhstan was given a large amount of money by the World Bank to restore water that had been diverted to other nations from the Aral Sea under Soviet rule.

Causes of Drought

A drought is mainly the cause of drier conditions. It is comparable to normal conditions that eventually lead to water supply problems. Really hot temperatures which eventually cause the moisture to evaporate from the soil can make drought worse. If any region is hot and dry, it doesn’t always mean that it is going through a drought. The dry season greatly increases drought occurrence. It is characterized by its low humidity, with watering holes and cracks, and rivers drying up. Due to the lack of these watering holes, many animals unwillingly migrate. This migration is due to the lack of water in search of more fertile lands.

Land and water temperatures cause droughts. As the temperature increases, more water evaporates and severe weather conditions also increase. Landscapes and crops need more water for their survival and growth and thus the overall demand for water increases gradually. Drought also occurs by air circulation and weather patterns. The water we have today is all the water we ever have now. Water available is moved by the weather patterns in the air all around. This is changing constantly.

Soil moisture levels also lead to drought. There is the evaporation of water for the creation of clouds when the soil moisture depletes. Demand, need, and supply of water issues are also a cause of droughts. The demand for water by people can worsen the situation depending on how the region reacts. Especially when the weather conditions, temperatures, or air patterns push a region toward a drought. Excessive irrigation is excellent for papa contributing to drought.

FAQs on Droughts

Question 1: What are the consequences of drought?

Answer: Some common consequences of drought are:

• Diminished crop growth or yield productions.
• Dust bowls and Dust storms, when drought hits an area suffering from desertification and erosion.
• Habitat damage – affecting terrestrial and aquatic wildlife.
• Hunger– drought provides too little water for food crops and human beings.
• Malnutrition, dehydration and related diseases is a major consequence.
• Mass migration of people in search of food and water is very common.
• Shortages of water for industrial and domestic purposes.
• Fight over natural resources, including water and food.

Question 2: Is drought a natural disaster or a man-made disaster?

Answer: A natural hazard is a threat of a naturally occurring event that has a negative impact on the environment, humans, and their survival. This negative effect is a natural disaster. In simple words when the hazardous threat eventually happens and harms human life, we call the event a natural disaster.

Drought is a natural disaster. Lack of precipitation for a protracted period of time causes drought. This results in a water shortage which affects the ecosystem. While droughts occur naturally, human activity, such as water use and water management, can exacerbate the dry conditions of the region.

Question 3: How to prevent droughts.

Answer: To deal effectively with the drought, here are some measures:

• Interlinking of national water resources (rivers).
• Agriculture and irrigation patterns need change.
• Water transportation channels need to be maintained properly. Leakages are bad.
• Water-intensive industries should be away from water deficit regions.
• Accumulating as much as rainwater we could. Improving rain harvesting infrastructure. Building more check dams, a small run of the river projects, more farm-lakes, improving water table, using mulching techniques in farms.
• Water meters need to be in a place like electricity meters. Asking someone not to consume excess water unnecessarily has not given good results so far. Nobody can count water a water meter will do that.
• Have water trains on standby. Attach them to the units of disaster management teams. As soon as a possibility of drought arises in a region, the water train can reach there.
• We need to prevent deforestation and thus we require afforestation.
• Judicious use of water. Awareness that wasted water won’t come back easily.

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Original research article, different types of drought under climate change or geoengineering: systematic review of societal implications.

• 1 Feinstein International Center, Friedman School for Nutrition Science and Policy, Tufts University, Boston, MA, United States
• 2 Red Cross Red Crescent Climate Centre, The Hague, Netherlands
• 3 Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Santiago, Chile
• 4 Facultad de Ingeniería y Ciencias, Universidad Adolfo Ibáñez, Santiago, Chile
• 5 Climate System Analysis Group, University of Cape Town, Cape Town, South Africa
• 6 International Research Institute for Climate and Society, Climate School, International Research Institute for Climate and Society, Columbia University, Palisades, NY, United States
• 7 Faculty of Geo-Information Science and Earth Observation, University of Twente, Enschede, Netherlands
• 8 Department of Meteorology, University of Reading, Reading, United Kingdom

Climate change and solar geoengineering have different implications for drought. Climate change can “speed up” the hydrological cycle, but it causesgreater evapotranspiration than the historical climate because of higher temperatures. Solar geoengineering (stratospheric aerosol injection), on the other hand, tends to “slow down” the hydrological cycle while reducing potential evapotranspiration. There are two common definitions of drought that take this into account; rainfall-only (SPI) and potential-evapotranspiration (SPEI). In different regions of Africa, this can result in different versions of droughts for each scenario, with drier rainfall (SPI) droughts under geoengineering and drier potential-evapotranspiration (SPEI) droughts under climate change. However, the societal implications of these different types of drought are not clear. We present a systematic review of all papers comparing the relationship between real-world outcomes (streamflow, vegetation, and agricultural yields) with these two definitions of drought in Africa. We also correlate the two drought definitions (SPI and SPEI) with historical vegetation conditions across the continent. We find that potential-evapotranspiration-droughts (SPEI) tend to be more closely related with vegetation conditions, while rainfall-droughts (SPI) tend to be more closely related with streamflows across Africa. In many regions, adaptation plans are likely to be affected differently by these two drought types. In parts of East Africa and coastal West Africa, geoengineering could exacerbate both types of drought, which has implications for current investments in water infrastructure. The reverse is true in parts of Southern Africa. In the Sahel, sectors more sensitive to rainfall-drought (SPI), such as reservoir management, could see reduced water availability under solar geoengineering, while sectors more sensitive to potential-evapotranspiration-drought (SPEI), such as rainfed agriculture, could see increased water availability under solar geoengineering. Given that the implications of climate change and solar geoengineering futures are different in different regions and also for different sectors, we recommend that deliberations on solar geoengineering include the widest possible representation of stakeholders.

Introduction

Drought is one of the most complex climate-related hazards to define, because of the myriad of different ways in which lack of water can manifest in different climate zones and in relation to different societal needs. With climate change, different regions of the world are expected to see increasing or decreasing amounts of total annual precipitation, with a general trend toward “speeding up” the hydrological cycle, because a warmer atmosphere can hold more water and cause more precipitation ( IPCC, 2021 ). However, a warmer atmosphere could ultimately result in less water availability, even in some places with increasing total precipitation, due to increased evaporation rates and dry spells ( Haile et al., 2020 ; Naik and Abiodun, 2020 ; Oguntunde et al., 2020 ).

Under scenarios of solar geoengineering, in which humans block a portion of incoming sunlight to cool the planet, future temperatures are not as high as in climate change scenarios. In turn, the hydrological cycle also slows down, and models project that a geoengineering scenario that fully reduces anthropogenic warming would cause a decrease in total precipitation in many regions compared to today's climate ( Cheng et al., 2019 ; Simpson et al., 2019 ). To avoid problems caused by slowing down the hydrological cycle, Irvine et al. (2019) investigate the outcomes of a strategy that uses solar geoengineering to halve the global temperature increase, as compared to a complete offset of climate change induced temperature increase. Their results indicate that there is less of a drying effect for much of the world in this scenario, using potential evapotranspiration as a measure. While not necessarily the “ideal” level of geoengineering, this proposal is a more appropriate option if the intention is to avoid the type of reversing of climate processes that occurs when complete offset parameterization is used, and several other studies have also investigated ways of partially offsetting temperature changes ( Kravitz et al., 2014 ; Lee et al., 2020 ).

While the calculations involved with managing the appropriate amount of incoming solar radiation are already complex from a geophysical perspective, the definition of “sufficient management” must also include the impact on and feedback from socioeconomic variables. In short, people must clearly be part of the equation. There are the possibilities of experiencing benefits from geoengineering, such as cooler temperatures, a more stable climate, and increasing the ability of humans to manage planetary boundary level interactions related to acidification and improving the efficiency of soil carbon management ( Sovacool, 2021 ). The cost of addressing climate change with geoengineering either as a primary or complementary mechanism has been noted to be more cost effective than non-geoengineering related mitigation strategies. While benefits can be achieved, estimating the uncertainties in regional impacts can be difficult to quantify given traditional approaches, with the risk of large scale global systems failure if either processes are not designed proposal and/or governance structures do not function as planned ( Caldeira et al., 2013 ; Gardiner and Fragnière, 2018 ).

Given the complexity of these projections, the implications for rainfall and temperature under a future with climate change or with solar geoengineering are complex, involving a spatially-varying mix of changes to temperature and precipitation. For Africa, Abiodun et al. (2021) found that climate change is projected to decrease water availability due to increasing evaporation, while geoengineering would mitigate the increase in evaporation but also decrease total precipitation in many regions. However, it is not clear what these results mean for human systems, for example, to know whether existing water management plans will be affected by the two different scenarios. Here, we carry out a systematic review of how the different types of droughts under climate change or geoengineering might relate to societal outcomes.

One of the most commonly-used drought definitions is the Standardized Precipitation Index (SPI), as proposed by McKee et al. (1993) . SPI is a simple way to compare the extremity of rainfall deficits across regions and different timescales. The only input to SPI is total precipitation on a particular timescale, with 1 month through to 24 months being common temporal units of analysis.

Almost 20 years later, Vicente-Serrano et al. proposed a related drought definition, the Standardized Precipitation Evapotranspiration Index (SPEI), which would take into account the importance of potential evapotranspiration (PET) for water availability ( Vicente-Serrano et al., 2010 ). This index is calculated in a similar way to the SPI, but using PET as an input. PET can be estimated through multiple methods depending on data availability ranging from simple temperature and solar radiation based estimates such as Hargreaves ( Hargreaves and Samani, 1985 ), or more complex methods such as Penman-Monteith which includes wind speed and humidity. The rationale behind this drought definition was partly to be able to measure the importance of increasing temperatures with climate change on water availability ( Vicente-Serrano et al., 2010 ). Importantly, SPEI integrates potential or reference evapotranspiration which assumes essentially unrestricted moisture availability at the surface. In most cases this will be larger than actual evaporation. SPEI therefore represents the upper limit of potential moisture deficit.

When compared to a preindustrial climate, projections of climate change in Africa tend to include increases in extreme droughts as defined by SPEI, because of the inclusion of increasing temperatures which drive increases in PET. On the other hand projections of the impact of solar geoengineering tend to include more extreme droughts as defined by SPI, which only uses rainfall ( Abiodun et al., 2021 ).

In many regions of the world, there is little difference between SPI and SPEI variability, as demonstrated in analyses of their historical record. This is particularly true in non-arid regions, where drought is driven mostly by rainfall variability ( Fuentes et al., 2022 ). However, in a world with high temperature increases due to climate change, these two drought definitions might diverge further, as PET might play a larger role in some regions ( Noureldeen et al., 2020 ). Unfortunately, large uncertainties in observational data of temperature and precipitation limit our understanding of these two types of droughts, because the choice of input data in some regions of the world can have a greater impact on drought estimates than the choice of how drought is defined in the first place ( Hoffmann et al., 2020 ).

In this article, we seek to advance progress in understanding the spectrum of potential societal implications of various future drought scenarios through a comparison of projections under a scenario of climate change (generally more intense SPEI droughts) and a scenario of solar geoengineering (generally more intense SPI droughts) in Africa. Given that climate change and solar geoengineering would affect drought risk differently in different regions of Africa, we identify how outcomes could be different for different stakeholders across the continent. First, we carry out a systematic literature review to identify which societal outcomes are more sensitive to rainfall-only drought (SPI) or rainfall-and-potential-evapotranspiration drought (SPEI). We then review which regions within Africa are projected to see more frequent droughts under each definition, and discuss implications for common agriculture and water-related adaptation investments on the continent.

To identify which societal outcomes are more sensitive to SPI or SPEI, we carry out a systematic literature review of all studies comparing these two drought definitions in Africa. First, we searched Web of Science for all papers that include both the terms SPI, SPEI, as well as either the word “Africa” or the name of an African country. This returned 58 peer-reviewed journal articles.

Next, we screened each article to identify whether the paper correlated the SPI and SPEI datasets with a societal outcome variable. Variables included vegetation indices, crop yields, reservoir levels, and stream flows. Papers were not included if they simply correlated SPI and SPEI with each other or other rainfall-derived drought definitions. Papers were also excluded if they presented only correlations for one of the drought indices with societal outcome variables, without presenting results for the other index in order to compare the two. Twelve (12) articles were included in the final dataset. Here we present the results for each study on SPI, SPEI, and societal outcomes.

To complement the literature review, we carried out a global cross correlation of SPI and SPEI with a vegetation index based on the Normalized Difference Vegetation Index (NDVI). The calculation of SPI was done by aggregating monthly rainfall from the Climate Hazards Group InfraRed Precipitation with Station Data (CHIRPS version 2.0) dataset ( Funk et al., 2015 ) and applying a gamma distribution to the data as suggested by Stagge et al. (2015) . SPEI calculation was applied using monthly rainfall from CHIRPS and reference evapotranspiration calculated using the Food and Agriculture Organization (FAO) Penman Monteith equation ( Pereira et al., 2015 ). Reference evapotranspiration was estimated by combining monthly temperatures, wind and surface pressure data from the European Center for Medium-Range Weather Forecasts (ECMWF) Reanalysis v5 (ERA5) dataset ( Hoffmann et al., 2019 ) and monthly incoming shortwave radiation from the Famine Early Warning Systems Network (FEWS NET) Land Data Assimilation System (FLDAS; McNally et al., 2017 ). Then, SPEI was calculated using the log-logistic distribution as in ( Vicente-Serrano et al., 2010 ; Vicente-Serrano and Beguería, 2016 ).

The NDVI monthly data was derived by combining data from the third generation Global Inventory Modeling and Mapping Studies (GIMMS) from the Advanced Very High Resolution Radiometer (AVHRR; Pinzon and Tucker, 2014 ) and from the Moderate Resolution Imaging Spectroradiometer (MODIS; Didan, 2015 ). MODIS NDVI was resampled and harmonized to the GIMMS NDVI resolution using ordinary least square regression between datasets ( Mao et al., 2012 ). The standardization of NDVI was applied based on the calculation of z-scores as originally proposed by Peters et al. (2002) .

Then, the cross correlation between standardized indices was applied at each pixel. However, the different time series were previously prewhitened using an Autoregressive Integrated Moving Average (ARIMA) model to remove serial correlation ( Fuentes et al., 2022 ). Thus, this analysis was applied to calculate the maximum correlation between lags of 0 and 24 months.

To contextualize the analysis of societal outcomes, we reproduce here the results from Abiodun et al. (2021) , which depict the geographic distribution of changes to SPI and SPEI across Africa under a strong climate change scenario and a specific scenario solar geoengineering that fully offsets global temperature increases due to climate change. When we refer to “solar geoengineering,” we are referring specifically to stratospheric aerosol injection.

To understand possible societal consequences of SPI droughts (only rainfall) compared to SPEI droughts (potential evapotranspiration), we present the results of the systematic literature review. Of the 58 papers that included the terms SPI and SPEI in Africa, only 12 showed results that correlated both SPI and SPEI with an outcome variable.

There were three main types of outcomes investigated in these papers: streamflow, agricultural yields, and vegetation. In the studies correlating SPI and SPEI with streamflow, SPI (rainfall only) often had a higher correlation than SPEI (potential evapotranspiration). These studies included two basins in West Africa (Volta and Niger), the Blue Nile in East Africa, and the Olifants Basin in South Africa ( Table 1 ).

Table 1 . Results of systematic literature review, which yielded 12 papers satisfying the criteria.

The four papers relating SPI and SPEI to agricultural yields found differing results, with each drought indicator showing stronger relationships to different crops or in different regions. Most of these differences in correlations were not strong (e.g., within 0.05 of each other), and therefore do not indicate that one drought definition is better linked to crop yields. See Table 1 for details of each study.

In studies that examined the correlation between the drought definitions and vegetation conditions, results were spatially variable, but more consistent than for agricultural yields. In many regions, researchers found that SPEI had higher correlations with vegetation indices (NDVI) than correlations between SPI and NDVI. Because agricultural yields are influenced by irrigation and other factors, it stands to reason that crop yields could respond less consistently to drought indicators than the unmediated response of rainfed vegetation.

To confirm the results from this literature review, we carry out a global cross correlation of SPI and SPEI with the Standardized Vegetation Index (based on NDVI), once these series were prewhitened (see Methods section). Results are depicted in Figure 1 , demonstrating the highest correlation between drought and vegetation at any time lag of 0–24 months. In these historical datasets, SPEI demonstrates higher correlations with vegetation in many parts of the world, especially in dry climate zones, including parts of East Africa, Southern Africa, and the Sahel. SPI and SPEI are highly correlated with each other in many tropical or wet regions of the world, and therefore show smaller differences in terms of correlation with outcome variables in those regions.

Figure 1 . Correlations (A) between SPI and SPEI; (B) between SPI and vegetation conditions, and (C) between SPEI and vegetation conditions. (B,C) correspond to the maximum correlation at each pixel for a 0-month to a 24-month time lag between prewhitened SPI/SPEI and the prewhitened vegetation condition response. (D) The difference between the two correlations: the SPEI correlation minus the SPI correlation.

Different regions of Africa have different projections for SPI (rainfall) droughts and SPEI (potential evapotranspiration) droughts under different scenarios of climate change and geoengineering. Abiodun et al. (2021) examined projections of climate change using a single climate model, the Community Earth System Model (CESM1) with 20 ensemble members under the RCP 8.5 scenario, and compared this with a scenario of solar geoengineering from the Stratospheric Aerosol Geoengineering Large Ensemble (GLENS) Project. In this experiment the stratospheric injection rate is calculated to maintain the global mean temperature as well as the inter-hemispheric and equator-to-pole near-surface temperatures at the 2020 level until the end of the century while keeping other forcing as in the RCP 8.5 scenario. This is a very high emissions scenario. Figure 2 is a reproduction of their results, depicting regions of Africa that could see increasing or decreasing frequency of drought as defined by SPI or SPEI under the two future scenarios. Adaptation investments in each region are likely to see a different set of trade-offs under each scenario.

Figure 2 . Frequency of drought occurrence per decade. The top row shows droughts as defined by SPI (water only), while the bottom row shows droughts as defined by SPEI (including potential evapotranspiration). The leftmost column (A,E) depicts the present-day frequency of droughts, the next column shows the change in frequency of SPI (B) and SPEI (F) droughts under solar geoengineering, compared to present. The third column shows the change in frequency of SPI (C) and SPEI (G) droughts between solar geoengineering and climate change. The last column (D,H) shows the difference between the solar geoengineering scenario and the climate change scenario. Data from Abiodun et al. (2021) .

In parts of East Africa and coastal west Africa, this scenario of solar geoengineering (maintaining global temperature) is projected to cause an increase in drought compared to climate change, regardless of which drought definition is used. In these regions, the increase of rainfall due to climate change overcomes the increase in evaporation from temperature increases, so the RCP 8.5 projections are for wetting of SPI and SPEI, while geoengineering is for drying of SPI and SPEI.

In other regions, the drought definition matters. In the Sahel, climate change is projected to make SPI (precipitation) droughts wetter, but make SPEI (potential evapotranspiration) droughts drier. Under the solar geoengineering scenario, these two trends are reversed, with projections indicating a wetter SPEI and drier SPI. In this case, communities reliant on streamflow for flood recession agriculture or irrigation (e.g., Sall et al., 2020 ) could face water problems in a geoengineered climate under less rainfall, as could those reliant on wetlands for grazing during the dry season (e.g., Adams, 1993 ). Extending beyond SPI, it is worth considering how climate change and solar geoengineering could affect the seasonality of river flows, with there being robust evidence of a change in flood timing with decadal climate variability ( Ficchı̀ and Stephens, 2019 ).

It is worth noting that the latitude at which aerosols are injected can affect the Inter-tropical Convergence Zone, which is a main influence on rainfall in the Sahel and many other regions. Other designs of solar geoengineering, other than the one explored here, could have different consequences for these regions ( Krishnamohan and Bala, 2022 ).

Lastly, there are several regions in which the solar geoengineering scenario reduces drought relative to the climate change scenario, regardless of which drought definition is used. In Southern Africa, for example, projections for SPI (rainfall) droughts under climate change and geoengineering are similar, but projections for SPEI (potential evapotranspiration) droughts are drier under climate change.

In all regions, people are managing their current climate and preparing adaptations for future changes ( Caretta et al., 2022 ). Table 2 lists several of the water-related adaptation measures that have been documented as climate change adaptation efforts in Africa ( Williams et al., 2021 ). These are categorized into three groups: adaptations related to food and ecosystems that are likely sensitive to SPEI (potential evapotranspiration), and those that are related to water supply management, which are likely sensitive to SPI (rainfall amounts). The two possible future scenarios of climate change and solar geoengineering are likely to have different implications for the success of these adaptation investments.

Table 2 . Examples of climate change adaptations in Africa as documented in Williams et al. (2021) , which are likely sensitive to differences in future scenarios in which SPI and SPEI change.

In parts of East Africa and coastal West Africa, adaptation investments which intend to address the risk of a wetter climate under climate change may be less useful in a future with solar geoengineering. In these regions, models project an increase in the frequency of droughts, in both SPEI and SPI, that may occur under geoengineering in regions that otherwise would not experience such change. Some communities and ecosystems could be negatively affected, and tradeoffs need to be studied and properly addressed before considering implementation. This is particularly the case for longer-term adaptation investments, such as infrastructure investments, which will last many decades and operate during future scenarios of climate change or geoengineering. To estimate how outcomes might vary over time, further research is needed on the relationships between decadal variability, longer term climate change, and solar geoengineering. Adaptation actions that are robust to projected increases or decreases in water availability over time might be favored.

In the Sahel, water management adaptations in sectors sensitive to SPEI, such as vegetation and agriculture, could see an improvement in drought outcomes under solar geoengineering, as this geoengineering scenario is wetter than the climate change scenario. However, people working in streamflow management, such as construction of dams, reservoirs, and irrigation, or promoting flood recession agriculture as an adaptation strategy (e.g., Sidibe et al., 2016 ) could see an exacerbation of drought conditions under geoengineering, because these sectors are likely more sensitive to the total precipitation amount, measured by SPI.

The implications of solar geoengineering relative to climate change are not uniform, and they differ by region and sector. Within Africa, there are regions in which both scenarios exacerbate droughts, regions where both future scenarios reduce droughts, and scenarios where climate change and geoengineering cause different types of droughts. Regional differences include places that might benefit easily from the outcomes of geoengineering, and other regions that might need to adjust their development plans if geoengineering is implemented.

These different types of droughts are likely to have different societal implications. Vegetation is likely most sensitive to drought defined as potential evapotranspiration, while streamflows are likely most sensitive to drought defined purely by precipitation amounts. Therefore, different futures in which rainfall (SPI) droughts or potential evapotranspiration (SPEI) droughts are more or less frequent has implications for current adaptation planning. This is particularly relevant for regions that are investing in water management infrastructure for the coming decades.

The projections for specific regions that are described here should be interpreted with caution, due to several sources of uncertainty in how this might play out in the future. First, the societal implications of drought are based on historical analyses, and this relationship between drought and outcomes could change under future scenarios as climate regimes and technologies change. Second, the climate projections here are derived from single models, and a larger multi-model ensemble might offer a wider range of possibilities. Third, the scenarios used here were extreme versions of climate change (RCP 8.5) and solar geoengineering (full offset of global temperature increase), and policy choices could select less dramatic pathways for our future. Lastly, the implementation of geoengineering could be done in different ways; we present results only from the GLENS scenario, which is only one representation of possible aerosol injections. Potentially affected populations should be at the table in discussions of geoengineering governance, because different scenarios will affect them differently.

The outcomes of “drought” are also not limited to climate trends alone. Streamflows, agriculture, and vegetation are also sensitive to non-climate factors, such as land-use change or excessive water extraction. For example, a study in Lake Chilwa Basin, Malawi concluded that rising temperatures were not able to explain declining lake levels, as neither timeseries of SPI nor SPEI related to the declining lake levels ( Kambombe et al., 2021 ). The authors speculated that land use change and other human activities were likely the dominant factors.

Given that SPI and SPEI droughts might affect crops, vegetation, and streamflow differently in different regions under different climate futures, it is dangerous to make broad generalizations that climate change or geoengineering would result in only winners or losers. Rather, scientists and practitioners need to acknowledge the full space of uncertainty about how these climate futures might affect different industries, and ensure that all voices are at the table when discussing research and deployment around solar geoengineering, given the wide variety of possible outcomes and ways in which people could be affected.

Data availability statement

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

Author contributions

EC designed the study, carried out the literature review, and drafted the article. IP analyzed the geoengineering data and created Figure 2 . IF analyzed the SPI/SPEI/NDVI data and created Figure 1 . CJ, ES, and AK provided inputs to the study design and text of the article. All authors contributed to the article and approved the submitted version.

The authors acknowledge the support by the Natural Environment Research Council (NERC) and Foreign, Commonwealth and Development Office (FCDO), formerly Department for International Development (grant number NE/P000525/1), under the Science for Humanitarian Emergencies and Resilience (SHEAR) research programme.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher's note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

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Keywords: climate change, geoengineering, drought, SPI, SPEI, Africa, streamflow, NDVI

Citation: Coughlan de Perez E, Fuentes I, Jack C, Kruczkiewicz A, Pinto I and Stephens E (2022) Different types of drought under climate change or geoengineering: Systematic review of societal implications. Front. Clim. 4:959519. doi: 10.3389/fclim.2022.959519

Received: 01 June 2022; Accepted: 18 August 2022; Published: 20 September 2022.

Reviewed by:

Copyright © 2022 Coughlan de Perez, Fuentes, Jack, Kruczkiewicz, Pinto and Stephens. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Erin Coughlan de Perez, erin.coughlan@tufts.edu

† ORCID: Erin Coughlan de Perez orcid.org/0000-0001-7645-5720 Ignacio Fuentes orcid.org/0000-0001-7066-7482 Christopher Jack orcid.org/0000-0002-0936-7277 Izidine Pinto orcid.org/0000-0002-9919-4559

This article is part of the Research Topic

Solar Geoengineering in the Horizon: Humanitarian Dimensions

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Droughts: Notes for UPSC Geograpahy

Drought is a phenomenon that comes under geography in the strict sense of the word but has reverberations across various fields. This is because droughts affect the livelihood and economies and even lives of people affected by it. Hence, it assumes importance for the UPSC exam. In this article, we talk about droughts for the IAS exam .

Definition of Drought

The term ‘Drought’ in simple words is the absence of water for a long period of time, at a place where it is considered abnormal as compared to its usual conditions. The distribution of water on the earth’s surface is not even. Some places have lots of freshwater e.g. rivers, lakes, lagoons, ponds etc.  and they are continuously replenished by rainfall and water from underground.

If a region that has had lots of rainfall , goes for a couple of weeks without rains, and people, animals and plants begin to experience a bit of dryness, it can be called a drought. Drought can be defined as a relatively long time where there is not enough water than there usually is, as a result of dry weather, to support human, animal and plant life. Droughts become an issue only when it begins to affect water supply for irrigation, municipal, industrial, energy, and ecosystem function. Severe droughts can have serious consequences.

Recently, the government of England has formally declared parts of England. It was declared after a period of prolonged hot and dry weather. 

The declaration of drought serves as a recognition of the water scarcity situation and the need for proactive measures to manage water resources effectively.

Implications of the declaration: The declaration abrings various actions and regulations to address the water scarcity issue and ensure the sustainable use of available water resources.

• Water Companies’ Drought Plans and Restrictions: Water companies are required to have a drought plan in place, outlining the restrictions they may implement on their customers during a drought. These plans serve as guidelines for managing water supplies efficiently and responsibly.
• Drought Orders and Permits for Water Management: During a drought, water companies have the option to apply for drought orders and permits. This helps ensure a more sustainable water supply during times of scarcity.
• Restrictions on Non-Essential Water Use: To conserve water during a drought, restrictions can be imposed on non-essential water use. This includes measures such as limiting water usage in commercial car washes and swimming pools. 
• Restrictions for Farmers: Farmers may face restrictions on water usage for spray irrigation. These measures are intended to balance the water needs of agricultural activities with the overall water availability in drought-affected areas.
• Government Intervention in Industrial and Food Processing Water Use: The government can impose restrictions on water use in industrial manufacturing or food processing sectors.
• Conservation Measures in Dry Conditions: In drought conditions, Natural England, the government’s conservation advisory body, may restrict access to certain areas, such as national nature reserves, if there is a risk of fire caused by dry conditions. These measures aim to protect valuable natural habitats and prevent wildfires, which can be exacerbated during periods of prolonged hot and dry weather.

Types of Drought

There are three types of droughts known to the scientific community:

• Meteorological drought occurs when there is a prolonged time with less than average precipitation. Such type of droughts can be triggered by a high level of reflected sunlight and above-average prevalence of high-pressure systems, winds carrying continental, rather than oceanic air masses.
• Agricultural droughts affect crop production or the ecology of the range. This condition can also arise independently from any change in precipitation levels when either increased irrigation or soil conditions and erosion triggered by poorly planned agricultural activities cause a shortfall in water available to the crops.
• Hydrological drought is brought about when the water reserves available in sources such as aquifers, lakes and reservoirs fall below a locally significant threshold. Hydrological drought tends to show up more slowly because it involves stored water that is used but not replenished. Like an agricultural drought, this can be triggered by more than just a loss of rainfall.
• Socio-Economic Drought  refers to the abnormal water shortage that affects socio economic condition of a region. 

For more notes on UPSC Geography , visit the linked article

• Drought-prone districts in India comprise nearly 1/6th of this country in terms of area. These areas receive an annual rainfall of around 60 cm or less.
• These situations can be attributed to human malpractices such asI recent year drought conditions have become recurring due to reasons as climate change, overuse of water resource, pollution, urbanization, etc. 
• Drought is declared by the respective State Governments taking into account rainfall situation, crop growth, etc.

Consequences of Drought

The effects of droughts can be divided into three groups: environmental, economic and social.

• Environmental effects: Lower surface and subterranean water-levels, lower flow-levels (with a decrease below the minimum leading to direct danger for amphibian life), increased pollution of surface water, the drying out of wetlands, more and larger fires, higher deflation intensity, loss of biodiversity , worse health of trees and the appearance of pests and dendroid diseases.
• Economic losses: Economic consequences include lower agricultural, forests, game and fishing output, higher food-production costs, lower energy-production levels in hydro plants, losses caused by depleted water tourism and transport revenue, problems with water supply for the energy sector and for technological processes in metallurgy, mining industries and disruption of water supplies for municipal economies.
• Social costs include the negative effect on the health of people directly exposed to this phenomenon (excessive heat waves), a possible limitation of water supplies, increased pollution levels, high food-costs, stress caused by failed harvests, etc. This explains why droughts and freshwater shortages operate as a factor which increases the gap between developed and developing countries.

Effects vary according to vulnerability. For example, subsistence farmers are more likely to migrate during drought because they do not have alternative food sources. Areas with populations that depend on water sources as a major food-source are more vulnerable to famine.

Frequently Asked Questions Related to Drought

What are the four types of drought.

As a result, the climatological community has defined four types of drought:

1) Meteorological drought 2) Hydrological drought 3) Agricultural drought 4) Socioeconomic drought.

Is a drought a natural disaster?

Droughts – UPSC Notes:- Download PDF Here

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What are The 4 Types of Drought?

• Apr 09, 2023
• 1.1 Meteorological drought
• 1.2 Hydrological drought
• 1.3 Agricultural drought
• 1.4 Socioeconomic drought

Drought is a natural disaster that is characterized by an extended period of dry weather conditions that can result in water shortages, crop failures, and adverse impacts on the environment, economy, and people’s livelihoods. In South Africa, drought is a recurrent problem that affects many parts of the country. Droughts can be classified into four different types, namely meteorological, hydrological, agricultural, and socioeconomic droughts. In this article, we will discuss each of these types of drought in detail.

Meteorological drought

Meteorological drought is a type of drought that is characterized by a prolonged period of below-average precipitation or rainfall. It occurs when the amount of rainfall in a region is insufficient to meet the normal water requirements of crops, vegetation, and livestock. This type of drought is usually caused by factors such as changes in global weather patterns, climate change, and El Niño.

Hydrological drought

Hydrological drought occurs when there is a prolonged period of below-average surface and groundwater availability in a region. It is caused by a lack of precipitation, high temperatures, and increased evaporation rates. This type of drought can result in reduced streamflow, lower groundwater levels, and reduced water storage capacity in reservoirs and dams.

Agricultural drought

Agricultural drought occurs when there is a prolonged period of below-average moisture levels in the soil. It affects the growth and yield of crops and can lead to crop failure, reduced agricultural productivity, and food shortages. This type of drought can be caused by factors such as low rainfall, high temperatures, and soil moisture deficits.

Socioeconomic drought

Socioeconomic drought occurs when the impacts of drought are felt on the economy and people’s livelihoods. It can be caused by factors such as reduced crop yields, increased food prices, decreased water availability, and reduced employment opportunities. Socioeconomic drought can also lead to increased poverty, migration, and social instability.

Meteorological Drought

Meteorological drought is the most common type of drought in South Africa. It occurs in regions where there is a prolonged period of below-average rainfall. The severity of meteorological drought is determined by comparing current rainfall patterns with historical averages. This type of drought is usually measured using the Standardized Precipitation Index (SPI) or the Palmer Drought Severity Index (PDSI).

The impact of meteorological drought in South Africa can be severe, with reduced water availability, lower crop yields, and increased food prices. The country has experienced several severe meteorological droughts in recent years, with the most notable being the drought that occurred between 2014 and 2018.

Hydrological Drought

Hydrological drought occurs when there is a prolonged period of below-average surface and groundwater availability. This type of drought is caused by a lack of precipitation, high temperatures, and increased evaporation rates. Hydrological drought can result in reduced streamflow, lower groundwater levels, and reduced water storage capacity in reservoirs and dams.

The impact of hydrological drought in South Africa can be severe, with reduced water availability for domestic, agricultural, and industrial use. The country has experienced several severe hydrological droughts in recent years, with the most notable being the drought that occurred between 2015 and 2018.

Agricultural Drought

Agricultural drought occurs when there is a prolonged period of below-average moisture levels in the soil. It affects the growth and yield of crops and can lead to crop failure, reduced agricultural productivity, and food shortages. This type of drought can be caused by factors such as low rainfall, high temperatures, and soil moisture deficits. The impact of agricultural drought in South Africa can be severe, with reduced crop yields, increased food prices, and food shortages.

Socioeconomic Drought

Socioeconomic drought is another type of drought that impacts the economy and social welfare of the affected region. This type of drought is usually not caused by a lack of rainfall, but rather by a combination of factors such as poor governance, inadequate infrastructure, and socioeconomic conditions. Socioeconomic drought can cause food and water shortages, which can lead to malnutrition and other health problems. It can also result in increased poverty, loss of livelihoods, and social unrest. The most vulnerable groups affected by socioeconomic drought include the poor, women, and children. In South Africa, socioeconomic droughts have been prevalent in rural areas, where poverty and inadequate infrastructure are common.

Drought is a significant natural disaster that can have devastating impacts on the environment, economy, and social welfare of affected regions. In South Africa, droughts are a frequent occurrence, and different types of droughts can have varying impacts on the country’s different sectors. Meteorological drought is the most common type of drought in South Africa, and it results in a lack of rainfall, which impacts water resources, agriculture, and biodiversity. Hydrological drought, on the other hand, impacts water resources, particularly surface, and groundwater, leading to water scarcity, and reducing water availability for households, agriculture, and industry. Agricultural drought affects crop yields and food production, leading to food insecurity and increased food prices. Finally, socioeconomic drought is driven by inadequate governance, infrastructure, and socioeconomic conditions and affects the most vulnerable populations, particularly in rural areas.

To address the different types of droughts, the South African government, along with the private sector and civil society, should implement comprehensive strategies to increase water conservation and efficiency, develop and maintain infrastructure, promote the use of drought-resistant crops, and improve governance and socioeconomic conditions. The implementation of such strategies will help mitigate the negative impacts of droughts on South Africa’s environment, economy, and social welfare. Additionally, it is crucial to ensure that the most vulnerable groups are taken into account in drought management and response plans.

What are Ways the South African Government Can Reduce the Impact of Droughts?

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Informal water contracts could provide quicker, cheaper ways to reduce impact of droughts

by UNC Gillings School of Global Public Health

Droughts continue to overburden the systems and infrastructure that bring water to citizens and businesses. This is especially true in places like the western United States, where water resources are scarce, and the rules that determine who gets water mean that farmers and other landowners who use water for irrigation often have first priority.

Developing new water supplies by building new dams or digging new wells has become more expensive and difficult, so transferring rights to existing supplies from lower-value irrigated activities to higher-valued urban uses often makes sense. However, those with water rights must go through complicated and costly formal processes to sell or temporarily lease their water access to municipalities or industries that need it in times of crisis.

A new study, published recently in Earth's Future , proposes a new solution: cost-effective informal water contracts, which could be a quicker and more affordable way to bring water to cities and homes during droughts and other emergencies.

"We have growing demands for water by cities and other high-value industrial uses, but we don't have much more that we can tap, either from groundwater or surface water ," said senior author Greg Characklis, Ph.D., who is the W.R. Kenan Distinguished Professor of environmental sciences and engineering at the UNC Gillings School of Global Public Health and director of the Center on Financial Risk in Environmental Systems, a joint program between Gillings the UNC Institute for the Environment.

"So, during dry weather periods, it would make sense to find a solution for water to make its way to more highly valued uses, similar to what we do with other types of resources."

Informal water leases, the approach proposed in the study, give those who have legal rights to water an option to temporarily bypass the complex and expensive regulatory process of transferring those rights through use of a financial arrangement in which the seller agrees not to take the water to which they are entitled, leaving it in the stream for the buyer to divert using their existing right.

It is the avoidance of the formal transfer of the right from buyer to seller that enables more rapid and less expensive transfers. This can be useful during droughts, which are increasing in frequency and severity due to rising temperatures and climate change .

While formal regulatory approval considers important environmental and legal factors, as well as impacts on third parties who might be affected by the diverted water, the process can be complex and costly. Researchers in the study say that parties who enter into informal water agreements can use compensatory releases to address and compensate for any negative impact on the environment or third parties.

"Let's imagine," Characklis explained, "that an urban user was upstream of an irrigator, and the irrigator foregoes water withdrawals so that the urban user can divert it. This could impact the flow of water between the two, other users in this stretch of the stream or environmental quality. So, in a case like this, if the urban user wants to buy water from this irrigator, they might have to buy 25% more than they're actually going to use and leave that 25% in the stream to flow down to the fish."

Even with this additional cost, Characklis says the transfer would still be much quicker and less expensive than the formal transfer process.

The researchers in the study modeled this approach to informal leasing in the Upper Colorado River Basin using data available from the state of Colorado, where agencies have developed a network-based water system model, StateMod, as part of a broader push to make water rights , demand and supply data available online.

Results show that between 1950 and 2013, the state could have accrued $222 million in benefits by using informal leases to reallocate water from irrigators to urban users.

"We were able to do a lot of modeling and testing [in Colorado] because we had a tremendous amount of information," said lead author H.B. Zeff, Ph.D., formerly a research scientist at UNC-Chapel Hill who is now with the Bureau of Reclamation in Colorado.

"But this idea of informal transfers could probably be applied in almost any basin in the western U.S. that has a similar type of institutional structure—which is essentially all of them."

This research, completed in collaboration with Pat Reed, Ph.D., of Cornell University and Antonia Hadjimichael, Ph.D., at Penn State University, has broad implications as global climate change continues to put a strain on our environment. The study demonstrates one creative way to get water quickly to users in need during droughts. When informal water contracts are designed correctly, researchers say they can recreate the effect of a formal water sale for a fraction of the price.

"The inability to rapidly reallocate water during droughts is really a huge hole in our management of water resources ," Characklis said. "And this is a new conceptual idea for how we might do that."

Journal information: Earth's Future

Provided by UNC Gillings School of Global Public Health

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