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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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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In This Article Expand or collapse the "in this article" section Drought

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Drought by Woonsup Choi LAST REVIEWED: 25 September 2023 LAST MODIFIED: 25 September 2023 DOI: 10.1093/obo/9780199874002-0215

Drought is a natural disaster that has plagued human society throughout history. However, the meaning of drought varies by perspective and academic discipline, and the cause of drought is difficult to pinpoint. Despite the variation in its meaning, drought generally refers to the condition of an abnormally low amount of water for a given climate. Here the water can be precipitation, streamflow, soil moisture, groundwater, reservoir storage, and the like, but the lack of precipitation is a precursor for other types of drought. The lack of precipitation is often associated with anomalous atmospheric conditions such as atmospheric-circulation anomalies, higher-than-normal temperatures, and lower-than-normal relative humidity. Sea surface temperature anomalies may lead to sustained atmospheric-circulation anomalies. Drought defined as a lack of precipitation is often called meteorological or climatological drought. Other drought types can be classified within the context of the affected sectors, such as agricultural, hydrological, and socioeconomic drought. Agricultural drought generally refers to a lack of soil moisture, and hydrological drought refers to a lack of surface and subsurface water (e.g., streamflow and groundwater). Socioeconomic drought hampers human activities such as industry or water supply. As meteorological drought persists, other types of drought can follow. Such definitions of drought are regarded as conceptual definitions, but operational ones are also necessary for quantitative understanding and management of drought events. Operational definitions use quantitative indices to identify the occurrence and characteristics of drought events such as onset, duration, termination, deficit volume, and spatial extent of drought. Much of existing drought research concerns developing, revising, and applying drought indices to investigate spatial and temporal patterns of drought at various geographical scales. Drought research has progressed along several directions, such as causes and drivers of drought, characteristics of drought events, impacts, and mitigation. Each of these directions is represented by the works cited in this article.

One of the most important issues in drought research is how to conceptualize and define droughts. Cook 2019 , Wilhite and Glantz 1985 , and Mishra and Singh 2010 offer a review of drought concepts, definitions, classification, and indices, and Robeson 2008 reviews research topics in drought that are relevant to applied climatology. There are numerous quantitative indices of drought, and the PDSI (Palmer Drought Severity Index) developed in Palmer 1965 and the SPI (Standardized Precipitation Index) developed in McKee, et al. 1993 are widely used as operational definitions of meteorological drought. The authors of Byun and Wilhite 1999 developed the EDI (Effective Drought Index) while criticizing SPI. Yevyevich 1967 suggests a threshold-level approach to defining hydrological droughts. Van Loon 2015 offers a comprehensive review of hydrological drought, and Van Loon, et al. 2016 reframes the approach to drought with regard to human activities. Tallaksen and van Lanen 2004 collects chapters in various aspects of drought in streamflow and groundwater.

Byun, Hi-Ryong, and Donald A. Wilhite. “Objective Quantification of Drought Severity and Duration.” Journal of Climate 12.9 (1999): 2747–2756.

DOI: 10.1175/1520-0442(1999)012<2747:OQODSA>2.0.CO;2

Discusses major existing drought indices and proposes EDI, which diagnoses meteorological drought by using daily precipitation while giving more weight to recent precipitation than precipitation more distant in the past. An authoritative reference for EDI.

Cook, Benjamin I. Drought: An Interdisciplinary Perspective . New York: Columbia University Press, 2019.

DOI: 10.7312/cook17688

A comprehensive and concise volume that explains drought in various perspectives, including hydroclimatology, climate change, land management, and groundwater. One of the best introductions for those who pursue scientific understanding of drought and good as an undergraduate-level textbook.

McKee, Thomas B., Nolan J. Doesken, and John Kleist. “The Relationship of Drought Frequency and Duration to Time Scales.” Proceedings of the 8th Conference on Applied Climatology 7.22 (1993): 179–183.

Defines drought on the basis of standardized precipitation, which is the difference between precipitation for a particular period and the mean divided by the standard deviation. The mean and standard deviation are determined from historical data. The standardized precipitation is expressed as SPI for varying lengths; for example, one month (SPI-1), three months (SPI-3), twelve months (SPI-12), etc. A common reference for SPI.

Mishra, Ashok K., and Vijay P. Singh. “A Review of Drought Concepts.” Journal of Hydrology 391.1–2 (2010): 202–216.

DOI: 10.1016/j.jhydrol.2010.07.012

Reviews a wide range of issues related to drought, including need for drought research, drought definitions and classification, drought indices, and relationship between drought and large-scale climate indices. One of the best introductions for those who pursue scientific understanding of drought.

Palmer, Wayne C. Meteorological Drought . Washington, DC: US Department of Commerce, 1965.

An authoritative reference for PDSI. Defines drought severity and duration, considering water balance components as well as precipitation. The PDSI numbers are classified by levels of dryness and wetness.

Robeson, Scott M. “Applied Climatology: Drought.” Progress in Physical Geography 32.3 (2008): 303–309.

DOI: 10.1177/0309133308091951

Reviews major research fields in drought from an applied-climatology perspective, focused on monitoring, climate change impacts, and modeling.

Tallaksen, Lena M., and Henny A. J. van Lanen, eds. Hydrological Drought: Processes and Estimation Methods for Streamflow and Groundwater . Amsterdam: Elsevier, 2004.

A collection of chapters addressing drought in streamflow and groundwater. Chapters about the science or management of drought are adequate for entry-level graduate students, but those about drought estimation methods are highly technical.

Van Loon, Anne F. “Hydrological Drought Explained.” Wiley Interdisciplinary Reviews: Water 2.4 (2015): 359–392.

DOI: 10.1002/wat2.1085

Provides a comprehensive review of hydrological drought, including typology and indices and discusses research gaps and challenges.

Van Loon, Anne F., Kerstin Stahl, Giuliano Di Baldassarre, et al. “Drought in a Human-Modified World: Reframing Drought Definitions, Understanding, and Analysis Approaches.” Hydrology and Earth System Sciences 20.9 (2016): 3631–3650.

DOI: 10.5194/hess-20–3631–2016

Emphasizes the impact of humans on drought, particularly hydrological drought, and reframes the way that drought is defined and analyzed in the Anthropocene. Clarifies drought terminology and identifies research gaps in drivers, modifiers, impacts, feedbacks, and baselines of drought.

Wilhite, Donald A., and Michael H. Glantz. “Understanding the Drought Phenomenon: The Role of Definitions.” Water International 10.3 (1985): 111–120.

DOI: 10.1080/02508068508686328

Provides detailed discussion of drought definitions. Suggests subdividing the definitions into four types on the basis of disciplinary perspectives (meteorological, agricultural, hydrological, and socioeconomic), and such a classification has been widely adopted in the literature, including the review in Mishra and Singh 2010 .

Yevyevich, Vujica M. “ An Objective Approach to Definitions and Investigations of Continental Hydrologic Droughts .” Hydrology Papers, Colorado State University 23 (1967).

Suggests an “objective” definition of hydrological droughts at continental or large-area scales. It is regarded as the first work that defined droughts by using runs of the sequence of a variable, where droughts are defined in terms of duration, deficit volume, and intensity. Most papers investigating hydrological droughts cite this paper.

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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

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Drought Types

• Meteorological Drought  is based on the degree of dryness or rainfall deficit and the length of the dry period.
• Hydrological Drought  is based on the impact of rainfall deficits on the water supply such as stream flow, reservoir and lake levels, and ground water table decline.
• Agricultural Drought  refers to the impacts on agriculture by factors such as rainfall deficits, soil water deficits, reduced ground water, or reservoir levels needed for irrigation.
• Socioeconomic Drought  considers the impact of drought conditions (meteorological, agricultural, or hydrological drought) on supply and demand of some economic goods such as fruits, vegetables, grains and meat. Socioeconomic drought occurs when the demand for an economic good exceeds supply as a result of a weather-related deficit in water supply.

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