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A drought is an event of prolonged shortages in the water supply, whether atmospheric (below-average
precipitation In meteorology Meteorology is a branch of the (which include and ), with a major focus on . The study of meteorology dates back , though significant progress in meteorology did not begin until the 18th century. The 19th century saw mod ...

precipitation
),
surface water An example of surface water is Lake Kinney. Surface water is water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which ...
or
ground water Groundwater is the water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydro ...
. A drought can last for months or years, or may be declared after as few as 15 days. It can have a substantial impact on the
ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...

ecosystem
and
agriculture Agriculture is the science, art and practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary Image:Family watching television 1958.jpg, Exercise trends, Increases in sedentary behaviors su ...

agriculture
of the affected region and harm to the local
economy An economy (; ) is an area of the production Production may be: Economics and business * Production (economics) * Production, the act of manufacturing goods * Production, in the outline of industrial organization, the act of making products ( ...

economy
. Annual dry seasons in the
tropics The tropics are the region of Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% i ...

tropics
significantly increase the chances of a drought developing and subsequent bush fires. Periods of heat can significantly worsen drought conditions by hastening evaporation of
water vapour (99.9839 °C) , - , Boiling point , , - , specific gas constant , 461.5 J/( kg·K) , - , Heat of vaporization , 2.27 MJ/kg , - , Heat capacity , 1.864 kJ/(kg·K) Water vapor, water vapour or aqueous vapor is the gaseous p ...

water vapour
. Drought is a recurring feature of the climate in most parts of the world. However, these regular droughts have become more extreme and more unpredictable due to
climate change Contemporary climate change includes both the global warming caused by humans, and its impacts on Earth's weather patterns. There have been previous periods of climate change, but the current changes are more rapid than any known even ...
. In fact studies based on
dendrochronology Dendrochronology (or tree-ring dating) is the scientific method The scientific method is an Empirical evidence, empirical method of acquiring knowledge that has characterized the development of science since at least the 17th century. It in ...
, or tree rings dating, confirm that drought affected by global warming goes back to 1900. Many plant species, such as those in the family Cactaceae (or
cacti A cactus (plural cacti, cactuses, or less commonly, cactus) is a member of the plant Plants are predominantly photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living thi ...

cacti
), have
drought tolerance Drought tolerance is the ability to which a maintains its biomass production during or conditions. Some plants are naturally adapted to dry conditions'','' surviving with protection mechanisms such as , , or repair of embolism. Other plants, spe ...
adaptations like reduced leaf area and waxy cuticles to enhance their ability to tolerate drought. Some others survive dry periods as buried seeds. Semi-permanent drought produces arid biomes such as deserts and grasslands. Prolonged droughts have caused
mass migration Mass migration refers to the migration Migration, migratory, or migrate may refer to: Human migration * Human migration, physical movement by humans from one region to another ** International migration, when peoples cross state boundaries and s ...
s and humanitarian crisis. Most arid ecosystems have inherently low productivity. The most prolonged drought ever in the world in
recorded history Recorded history or written history is a historical narrative History (from Ancient Greek, Greek , ''historia'', meaning "inquiry; knowledge acquired by investigation") is the study of the past. Events occurring before the History of writing ...
occurred in the
Atacama Desert
Atacama Desert
in
Chile Chile, officially the Republic of Chile, is a country in the western part of South America South America is a entirely in the and mostly in the , with a relatively small portion in the . It can also be described as the southern ...

Chile
(400 Years). Throughout history, humans have usually viewed droughts as "disasters" due to the impact on food availability and the rest of society. Humans have often tried to explain droughts as either a
natural disaster A natural disaster is a major adverse event An adverse event (AE) is any untoward medical occurrence in a patient or clinical investigation subject administered a pharmaceutical product and which does not necessarily have a causal relationsh ...
, caused by humans, or the result of
supernatural The supernatural encompasses supposed phenomena or entities that are not subject to the . This term is attributed to , such as s, s, , and . It also includes claimed abilities embodied in or provided by such beings, including , , , , and . Th ...

supernatural
forces. It is among the earliest documented climatic events, present in the
Epic of Gilgamesh The ''Epic of Gilgamesh'' () is an epic poem An epic poem is a lengthy narrative poem, ordinarily involving a time beyond living memory in which occurred the extraordinary doings of the extraordinary men and women who, in dealings with ...
and tied to the
Biblical The Bible (from Koine Greek Koine Greek (, , Greek approximately ;. , , , lit. "Common Greek"), also known as Alexandrian dialect, common Attic, Hellenistic or Biblical Greek, was the koiné language, common supra-regional form of Greek ...

Biblical
story of
Joseph Joseph is a common masculine given name, derived from the Hebrew Yosef (יוֹסֵף). The form "Joseph" is used mostly in English, French and partially German-speaking (alongside "Josef") countries. This spelling is also found as a variant in th ...
's arrival in and the later
Exodus Exodus or the Exodus may refer to: Religion *Book of Exodus, second book of the Hebrew Torah and the Christian Bible *The Exodus, the biblical story of the migration of the ancient Israelites from Egypt into Canaan Historical events * Jujuy E ...

Exodus
from
Ancient Egypt Ancient Egypt was a civilization  A civilization (or civilisation) is a that is characterized by , , a form of government, and systems of communication (such as ). Civilizations are intimately associated with additional char ...

Ancient Egypt
. Hunter-gatherer migrations in 9,500 BC Chile have been linked to the phenomenon, as has the exodus of early humans
out of Africa ''Out of Africa'' is a memoir A memoir (; , ) is any nonfiction Nonfiction (also spelled non-fiction) is any document A document is a writing, written, drawing, drawn, presented, or memorialized representation of thought, often the manif ...
and into the rest of the world around 135,000 years ago.
Rituals A ritual is a sequence of activities involving gesture A gesture is a form of non-verbal communication or non-vocal communication Communication (from Latin ''communicare'', meaning "to share") is the act of developing Semantics, meaning ...
exist to prevent or avert drought,
rainmaking Rainmaking, also known as artificial precipitation, artificial rainfall and pluviculture, is the act of attempting to artificially induce or increase precipitation In meteorology Meteorology is a branch of the atmospheric sciences which ...
could go from dances to
scapegoating Scapegoating is the practice of singling out a person or group for unmerited blame and consequent negative treatment. Scapegoating may be conducted by individuals against individuals (e.g. "he did it, not me!"), individuals against groups (e.g., ...
to
human sacrifice Human sacrifice is the act of killing one or more humans as part of a ritual A ritual is a sequence of activities involving gestures, words, actions, or objects, performed in a sequestered place and according to a set sequence. Rituals may be ...
s. Nowadays, those ancient practices are for the most part relegated to
folklore Folklore is the expressive body of culture shared by a particular group of people; it encompasses the tradition A tradition is a belief A belief is an attitude Attitude may refer to: Philosophy and psychology * Attitude (psycholog ...

folklore
and replaced by more rational
water management Water resource management is the activity of planning, developing, distributing and managing the optimum use of water resources. It is an aspect of water cycle management. Water is essential for our survival. The field of water resources manageme ...
.


Types

People tend to define droughts in three main ways: #
Meteorological Meteorology is a branch of the atmospheric sciences which includes atmospheric chemistry and atmospheric physics, with a major focus on weather forecasting Weather forecasting is the application of science and technology to predict the ...
drought occurs when there is a prolonged time with less than average precipitation. Meteorological drought usually precedes the other kinds of drought. #
Agricultural Agriculture is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary Image:Family watching television 1958.jpg, Exercise trends, Increases in sedentary behaviors such as watching tele ...

Agricultural
droughts affect crop production or the ecology of the
range Range may refer to: Geography * Range (geographic)A range, in geography, is a chain of hill A hill is a landform A landform is a natural or artificial feature of the solid surface of the Earth or other planetary body. Landforms together ...
. This condition can also arise independently from any change in precipitation levels when either increased
irrigation Irrigation is the agricultural Agriculture is the science, art and practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated Domesti ...

irrigation
or
soil Surface-water- gley developed in glacial till, Northern Ireland.">Northern_Ireland.html" ;"title="glacial till, Northern Ireland">glacial till, Northern Ireland. Soil is a mixture of organic matter, minerals, gases, liquids, and organisms tha ...

soil
conditions and erosion triggered by poorly planned agricultural endeavors cause a shortfall in water available to the crops. However, in a traditional drought, it is caused by an extended period of below average precipitation. #
Hydrological Hydrology (from Greek: ὕδωρ, "hýdōr" meaning "water" and λόγος, "lógos" meaning "study") is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water re ...
drought is brought about when the water reserves available in sources such as
aquifer An aquifer is an underground layer of -bearing , rock fractures or unconsolidated materials (, , or ). can be extracted using a water . The study of water flow in aquifers and the characterization of aquifers is called . Related terms include a ...

aquifer
s,
lake A lake is an area filled with water, localized in a basin, surrounded by land Land is the solid surface of Earth that is not permanently submerged in water. Most but not all land is situated at elevations above sea level (variable ove ...

lake
s and
reservoir A reservoir (; from French ''réservoir'' ) is most commonly an enlarged natural or artificial lake A lake is an area filled with water, localized in a basin, surrounded by land Land is the solid surface of Earth that is not per ...

reservoir
s 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. For instance, around 2007
Kazakhstan Kazakhstan ( kk, Қазақстан, Qazaqstan; russian: Казахстан, Kazakhstan), officially the Republic of Kazakhstan,; russian: Республика Казахстан, Respublika Kazakhstan, link=no) is a country located mainly in ...

Kazakhstan
was awarded a large amount of money by the
World Bank The World Bank is an international financial institution An international financial institution (IFI) is a financial institution that has been established (or chartered) by more than one country, and hence is subject to international law. Its o ...
to restore water that had been diverted to other nations from the
Aral Sea The Aral Sea (Aral ; kk, Aral teńizi, Арал теңізі, uz, Orol dengizi, Орол денгизи, kaa, Aral ten'izi, Арал теңизи, russian: Аральское море) was an endorheic lake lying between Kazakhstan Kaza ...

Aral Sea
under
Soviet The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a socialist state A socialist state, socialist republic, or socialist country, sometimes referred to as a workers' state or workers' republic, is a sovere ...
rule. Similar circumstances also place their largest lake,
Balkhash
Balkhash
, at risk of completely drying out. As a drought persists, the conditions surrounding it gradually worsen and its impact on the local population gradually increases.


Causes


Precipitation deficiency

Mechanisms of producing precipitation include
convective Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity Homogeneity and heterogeneity are concepts often used in the sciences and statistics Statistics ...
,
stratiform
stratiform
, and orographic rainfall. Convective processes involve strong vertical motions that can cause the overturning of the atmosphere in that location within an hour and cause heavy precipitation, while stratiform processes involve weaker upward motions and less intense precipitation over a longer duration. Precipitation can be divided into three categories, based on whether it falls as liquid water, liquid water that freezes on contact with the surface, or ice. Droughts occur mainly in areas where normal levels of rainfall are, in themselves, low. If these factors do not support precipitation volumes sufficiently to reach the surface over a sufficient time, the result is a drought. Drought can be triggered by a high level of reflected sunlight and above average prevalence of high
pressure system A pressure system is a relative peak or lull in the Atmospheric pressure#Mean sea level pressure, sea level pressure distribution. The surface pressure at sea level varies minimally, with the lowest value measured and the highest recorded . H ...
s,
wind Wind is the natural movement of air or other gases relative to a planet's surface. Wind occurs on a range of scales, from thunderstorm A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by th ...

wind
s carrying continental, rather than oceanic air masses, and ridges of
high pressure area A high-pressure area, high, or anticyclone, is a region where the atmospheric pressure Atmospheric pressure, also known as barometric pressure (after the barometer A barometer is a scientific instrument that is used to measure air pressure ...
s aloft can prevent or restrict the developing of thunderstorm activity or rainfall over one certain region. Once a region is within drought, feedback mechanisms such as local arid air, hot conditions which can promote warm core ridging, and minimal evapotranspiration can worsen drought conditions.


Dry season

Within the tropics, distinct, wet and dry
season A season is a division of the year based on changes in weather Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloud cover, cloudy. On Earth, most ...

season
s emerge due to the movement of the Intertropical Convergence Zone or
Monsoon trough The monsoon trough is a portion of the Intertropical Convergence Zone in the Western Pacific,Bin WangThe Asian Monsoon.Retrieved 2008-05-03. as depicted by a line on a weather map 250px, A surface weather analysis for the United States on Oct ...
. The dry season greatly increases drought occurrence, and is characterized by its low humidity, with watering holes and rivers drying up. Because of the lack of these watering holes, many grazing animals are forced to migrate due to the lack of water in search of more fertile lands. Examples of such animals are
zebras Zebras (, ) (subgenus ''Hippotigris'') are African equines with distinctive black-and-white striped Animal coat, coats. There are three Extant taxon, extant species: the Grévy's zebra (''Equus grevyi''), plains zebra (''E. quagga''), and the ...

zebras
,
elephants Elephants are the largest existing land animals. Three living species In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, ...

elephants
, and
wildebeest Wildebeest ( , , ), also called gnu ( or ), are antelope The term antelope is used to refer to many species of even-toed ruminant Ruminants (suborder In biological classification, the order ( la, wikt:ordo#Latin, ordo) is # a taxo ...

wildebeest
. Because of the lack of water in the plants, bushfires are common. Since water vapor becomes more energetic with increasing temperature, more water vapor is required to increase relative humidity values to 100% at higher temperatures (or to get the temperature to fall to the dew point). Periods of warmth quicken the pace of fruit and vegetable production, increase evaporation and transpiration from plants, and worsen drought conditions.


El Niño

Drier and hotter weather occurs in parts of the
Amazon River The Amazon River (, ; es, Río Amazonas, pt, Rio Amazonas) in South America South America is a entirely in the and mostly in the , with a relatively small portion in the . It can also be described as the southern of a single con ...

Amazon River
Basin,
Colombia Colombia ( , ; ), officially the Republic of Colombia, is a List of transcontinental countries, transcontinental country spanning South America and an Insular region of Colombia, insular region in North America. It is bordered by the Carib ...

Colombia
, and
Central America Central America ( es, América Central, , ''Centroamérica'' ) is a region of the Americas The Americas (also collectively called America) is a landmass comprising the totality of North North is one of the four compass points or ...

Central America
during El Niño events. Winters during the El Niño are warmer and drier than average conditions in the Northwest, northern Midwest, and northern Mideast United States, so those regions experience reduced snowfalls. Conditions are also drier than normal from December to February in south-central Africa, mainly in
Zambia Zambia (), officially the Republic of Zambia (Bemba language, Bemba:'' Icalo ca Zambia''; Tonga language (Zambia and Zimbabwe), Tonga: ''Cisi ca Zambia''; Lozi language, Lozi: ''Naha ya Zambia''; Chewa language, Nyanja: ''Dziko la Zambia''), ...

Zambia
,
Zimbabwe Zimbabwe (), officially the Republic of Zimbabwe, is a landlocked country A landlocked country is a country A country is a distinct territory, territorial body or political entity. It is often referred to as the land of an individ ...

Zimbabwe
,
Mozambique Mozambique (), officially the Republic of Mozambique ( pt, Moçambique or , ; ny, Mozambiki; sw, Msumbiji; ts, Muzambhiki), is a country located in Southeastern Africa bordered by the Indian Ocean The Indian Ocean is the third-lar ...

Mozambique
, and
Botswana Botswana (, also ), officially the Republic of Botswana ( tn, Lefatshe la Botswana, label=Setswana; Kalanga language, Kalanga: ''Hango yeBotswana''), is a landlocked country in Southern Africa. Botswana is topographically flat, with up to 70 ...

Botswana
. Direct effects of El Niño resulting in drier conditions occur in parts of
Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia or SEA, is the geographical United Nations geoscheme for Asia#South-eastern Asia, southeastern subregion of Asia, consisting of the regions ...

Southeast Asia
and
Northern Australia The unofficial geographic term Northern Australia includes those parts of Queensland Queensland ( ,) is a state situated in northeastern Australia, and is the States and territories of Australia, second-largest and third-most populous Aust ...

Northern Australia
, increasing
bush fire Bush or Bushes may refer to: * Bush (plant), a shrub or small tree * "The bush", rural, undeveloped land or country areas *Slang term for (often female, untrimmed) pubic hair People * Bush (surname), including any of several people with that nam ...
s, worsening
haze Haze is traditionally an in which dust, smoke, and other dry obscure the clarity of the sky. The manual of codes includes a classification of horizontal obscuration into categories of fog, , , , haze, smoke, , dust, sand, and snow. Sou ...

haze
, and decreasing air quality dramatically. Drier-than-normal conditions are also in general observed in
Queensland Queensland ( ) is a state situated in northeastern Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the ...

Queensland
, inland
Victoria Victoria most commonly refers to: * Victoria (Australia), a state of the Commonwealth of Australia * Victoria, British Columbia, provincial capital of British Columbia, Canada * Victoria (mythology), Roman goddess of Victory * Victoria, Seychelles ...
, inland
New South Wales New South Wales (abbreviated as NSW) is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspape ...
, and eastern
Tasmania Tasmania (), abbreviated as TAS, is an island An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent land features on atol ...
from June to August. As warm water spreads from the west Pacific and the
Indian Ocean The Indian Ocean is the third-largest of the world's five ocean The ocean (also the or the world ocean) is the body of that covers approximately 70.8% of the surface of and contains 97% of . Another definition is "any of the large ...

Indian Ocean
to the east Pacific, it causes extensive drought in the western Pacific. Singapore experienced the driest February in 2014 since records began in 1869, with only 6.3 mm of rain falling in the month and temperatures hitting as high as 35 °C on 26 February. The years 1968 and 2005 had the next driest Februaries, when 8.4 mm of rain fell.


Erosion and human activities

Human activity can directly trigger exacerbating factors such as over farming, excessive
irrigation Irrigation is the agricultural Agriculture is the science, art and practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated Domesti ...

irrigation
,
deforestation deforestation in 1750-2004 (net loss) showing anthropogenic modification of remaining forest. File:MODIS (2020-08-01).jpg, 300px, Dry seasons, exacerbated by climate change, and the use of slash-and-burn methods for clearing tropical forest ...

deforestation
, and
erosion In earth science Earth science or geoscience includes all fields of natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific ...

erosion
adversely impact the ability of the land to capture and hold water. In arid climates, the main source of erosion is wind. Erosion can be the result of material movement by the wind. The wind can cause small particles to be lifted and therefore moved to another region (deflation). Suspended particles within the wind may impact on solid objects causing erosion by abrasion (ecological succession). Wind erosion generally occurs in areas with little or no vegetation, often in areas where there is insufficient rainfall to support vegetation.
Loess Loess (, ; from German ''Löss'' ) is a clastic, predominantly silt-sized sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently sediment transport, transported by ...
is a homogeneous, typically nonstratified, porous,
friable Friability ( ), the condition of being friable, describes the tendency of a solid Solid is one of the four fundamental states of matter (the others being liquid, gas and plasma). The molecules in a solid are closely packed together and c ...
, slightly coherent, often calcareous, fine-grained,
silt Silt is granular material A granular material is a conglomeration of discrete solid, macroscopic scale, macroscopic particles characterized by a loss of energy whenever the particles interact (the most common example would be friction when gra ...
y, pale yellow or buff, windblown ( Aeolian)
sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently sediment transport, transported by the action of wind, water, or ice or by the force of gravity acting on the particles. ...

sediment
. It generally occurs as a widespread blanket deposit that covers areas of hundreds of square kilometers and tens of meters thick. Loess often stands in either steep or vertical faces. Loess tends to develop into highly rich soils. Under appropriate climatic conditions, areas with loess are among the most agriculturally productive in the world. Loess deposits are geologically unstable by nature, and will erode very readily. Therefore, windbreaks (such as big trees and bushes) are often planted by farmers to reduce the wind erosion of loess. Wind erosion is much more severe in arid areas and during times of drought. For example, in the
Great Plains The Great Plains (french: Grandes Plaines), sometimes simply "the Plains", is a broad expanse of flatland ''Flatland: A Romance of Many Dimensions'' is a satire, satirical novella by the English schoolmaster Edwin Abbott Abbott, first publi ...
, it is estimated that soil loss due to wind erosion can be as much as 6100 times greater in drought years than in wet years.


Climate change

Global
climate change Contemporary climate change includes both the global warming caused by humans, and its impacts on Earth's weather patterns. There have been previous periods of climate change, but the current changes are more rapid than any known even ...
is expected to trigger droughts with a substantial impact on agriculture throughout the world, and especially in
developing nation Image:Imf-advanced-un-least-developed-2008.svg, 450px, Example of Older Classifications by the International Monetary Fund, IMF and the United Nations, UN from 2008 A developing country is a country with a less developed Industrial sector, i ...
s. Along with drought in some areas, flooding and erosion could increase in others. Some proposed solutions to global warming that focus on more active techniques,
solar radiation management Solar radiation management (SRM), or solar geoengineering, is a type of climate engineering in which sunlight (solar radiation) is reflected back to space to limit or reverse global warming Climate change includes both global warmin ...
through the use of a
space sunshade A space sunshade or sunshield is a Umbrella, parasol that wikt:divert, diverts or otherwise reduces some of a star's radiation, preventing them from hitting a spacecraft or planet and thereby reducing its insolation, which results in reduced heat ...
for one, may also carry with them increased chances of drought.''Sunshade' for global warming could cause drought''
2 August 2007
New Scientist ''New Scientist'' is a magazine A magazine is a periodical literature, periodical publication which is printing, printed in Coated paper, gloss-coated and Paint sheen, matte paper. Magazines are generally published on a regular schedule and ...
, Catherine Brahic
According to the
Special Report on Climate Change and Land The United Nations The United Nations (UN) is an intergovernmental organization that aims to maintain international peace and international security, security, develop friendly relations among nations, achieve international cooperation, and ...
of the
Intergovernmental Panel on Climate Change The Intergovernmental Panel on Climate Change (IPCC) is an intergovernmental body of the United Nations The United Nations (UN) is an intergovernmental organization that aims to maintain international peace and international security, s ...
, climate change increases drought and
desertification Desertification is a type of land degradation Land degradation is a process in which the value of the biophysical environment is affected by a combination of human-induced processes acting upon the land. It is viewed as any change or distu ...
. Hundreds of million people are affected. The affected area includes large territories in Africa, Asia, Australia, and South America.


Consequences

One can divide the effects of droughts and water shortages into three groups: environmental, economic and social. * In the case of 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 Biodiversity loss includes the extinction of species worldwide, as well as the local reduction or loss of species in a certain habitat, resulting in a loss of biological diversity. The latter phenomenon can be temporary or permanent, depending on w ...
, worse health of trees and the appearance of pests and dendroid diseases. * Economic losses 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, the chemical, paper, wood, foodstuff industries etc., 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), possible limitation of water supplies, increased pollution levels, high food-costs, stress caused by failed harvests, etc. This explains why droughts and fresh water 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. Drought can also reduce water quality, because lower water-flows reduce dilution of pollutants and increase
contamination Contamination is the presence of a constituent, impurity, or some other undesirable element that spoils, corrupts, infects, makes unfit, or makes inferior a material, physical body, natural environment, wiktionary:Workplace, workplace, etc. Type ...

contamination
of remaining water-sources. Common consequences of drought include: * Diminished crop growth or yield productions and
carrying capacity The carrying capacity of an environment Environment most often refers to: __NOTOC__ * Natural environment, all living and non-living things occurring naturally * Biophysical environment, the physical and biological factors along with their chemical ...
for
livestock Livestock are the domesticated Domestication is a sustained multi-generational relationship in which one group of organisms assumes a significant degree of influence over the reproduction and care of another group to secure a more predictabl ...
*
Dust bowl The Dust Bowl was a period of severe dust storm A dust storm, also called a sandstorm, is a meteorological phenomenon common in arid A region is arid when it is characterized by a severe lack of available water, to the extent o ...
s, themselves a sign of
erosion In earth science Earth science or geoscience includes all fields of natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific ...

erosion
, which further erode the
landscape A landscape is the visible features of an area of , its s, and how they integrate with or man-made features.''New Oxford American Dictionary''. A landscape includes the physical elements of ly defined s such as (ice-capped) , , such as s, s, ...

landscape
*
Dust storms A dust storm, also called sandstorm, is a meteorological phenomenon common in arid A region is arid when it is characterized by a severe lack of available water, to the extent of hindering or preventing the growth and development of pl ...
, when drought hits an area suffering from desertification and
erosion In earth science Earth science or geoscience includes all fields of natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific ...

erosion
*
Famine A famine is a widespread scarcity of food Food is any substance consumed to provide nutritional support for an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual con ...

Famine
*
Habitat Ibex in an alpine habitat In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical environment. ...

Habitat
damage, affecting both
terrestrial Terrestrial refers to things related to land Land is the solid surface of the Earth that is not permanently covered by water. The vast majority of human activity throughout history has occurred in land areas that support agriculture A ...
and
aquatic Aquatic means relating to water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known li ...

aquatic
wildlife *
Hunger In politics, humanitarian aid, and the social sciences, hunger is defined as a condition in which a person cannot eat sufficient food to meet basic nutritional needs for a sustained period. In the field of hunger relief, the term ''hunger'' ...

Hunger
– drought provides too little water to support food crops. *
Malnutrition Malnutrition is 'a state of nutrition in which a deficiency or excess (or imbalance) of energy, protein and other nutrients causes measurable adverse effect on tissue and body form (body shape, size and composition) and function and clinical ou ...
,
dehydration In physiology, dehydration is a lack of total body water In physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology Biology is the natural science that studies ...

dehydration
and related diseases *
Mass migration Mass migration refers to the migration Migration, migratory, or migrate may refer to: Human migration * Human migration, physical movement by humans from one region to another ** International migration, when peoples cross state boundaries and st ...
, resulting in
internal displacement Internal may refer to: *Internality as a concept in behavioural economics *Neijia, internal styles of Chinese martial arts *Neigong or "internal skills", a type of exercise in meditation associated with Daoism *''Internal (album)'' by Safia (band), ...
and international
refugee A refugee, generally speaking, is a displaced person Forced displacement (also forced migration) is an involuntary or coerced movement of a person or people away from their home or home region In geography, regions are areas that are broa ...

refugee
s * Reduced electricity production due to reduced water-flow through
hydroelectric Hydroelectricity, or hydroelectric power, is electricity produced from hydropower Hydropower (from el, ὕδωρ, "water"), also known as water power, is the use of falling or fast-running water Water (chemical formula H2O) is a ...
dam A dam is a barrier that stops or restricts the flow of surface water An example of surface water is Lake Kinney. Surface water is water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tast ...

dam
s * Shortages of water for
industrial Industrial may also refer to: Industry * Industrial archaeology, the study of the history of the industry * Industrial engineering, engineering dealing with the optimization of complex industrial processes or systems * Industrial loan company, a f ...
users *
Snake Snakes are elongated, limbless, carnivore, carnivorous reptiles of the suborder Serpentes . Like all other Squamata, squamates, snakes are ectothermic, amniote vertebrates covered in overlapping Scale (zoology), scales. Many species of snakes ...

Snake
migration, which results in snake-bites * Social unrest * War over natural resources, including water and food * Wildfires, such as Australian bushfires, become more common during times of drought and may cause human deaths. * Exposure and oxidation of acid sulfate soils due to falling surface- and ground-water levels.Mosley LM, Zammit B, Jolley A, and Barnett L (2014). Acidification of lake water due to drought. Journal of Hydrology. 511: 484–493.Mosley LM, Palmer D, Leyden E, Fitzpatrick R, and Shand P (2014). Acidification of floodplains due to river level decline during drought. Journal of Contaminant Hydrology 161: 10–23.Mosley LM, Palmer D, Leyden E, Fitzpatrick R, and Shand P (2014). Changes in acidity and metal geochemistry in soils, groundwater, drain and river water in the Lower Murray River after a severe drought. Science of the Total Environment 485–486: 281–291. * Cyanotoxin accumulation within food chains and water supply (some of which are among the most potent toxins known to science) can cause cancer with low exposure over the long term. High levels of microcystin appeared in San Francisco Bay Area salt-water shellfish and fresh-water supplies throughout the state of California in 2016.


Protection, mitigation and relief

Agriculturally, people can effectively mitigate much of the impact of drought through irrigation and crop rotation. Failure to develop adequate drought mitigation strategies carries a grave human cost in the modern era, exacerbated by population growth, ever-increasing population densities. Franklin D. Roosevelt, President Roosevelt on April 27, 1935, signed documents creating the Soil conservation, Soil Conservation Service (SCS)—now the Natural Resources Conservation Service (NRCS). Models of the law were sent to each state where they were enacted. These were the first enduring practical programs to curtail future susceptibility to drought, creating agencies that first began to stress soil conservation measures to protect farm lands today. It was not until the 1950s that there was an importance placed on water conservation was put into the existing laws (NRCS 2014). Strategies for drought protection, mitigation or relief include: * Dams – many dams and their associated reservoirs supply additional water in times of drought. * Cloud seeding – a form of intentional weather modification to induce rainfall. This remains a hotly debated topic, as the National Research Council (United States), United States National Research Council released a report in 2004 stating that to date, there is still no convincing scientific proof of the efficacy of intentional weather modification. * Desalination – use of sea water for irrigation or consumption. * Drought monitoring – Continuous observation of rainfall levels and comparisons with current usage levels can help prevent man-made drought. For instance, analysis of water usage in Yemen has revealed that their water table (underground water level) is put at grave risk by over-use to fertilize their Khat crop. Careful monitoring of moisture levels can also help predict increased risk for wildfires, using such metrics as the Keetch-Byram Drought Index or Palmer Drought Index. * Land use – Carefully planned crop rotation can help to minimize
erosion In earth science Earth science or geoscience includes all fields of natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific ...

erosion
and allow farmers to plant less water-dependent crops in drier years. * Outdoor water-use restriction – Regulating the use of sprinklers, hoses or buckets on outdoor plants, filling pools, and other water-intensive home maintenance tasks. Xeriscaping yards can significantly reduce unnecessary water use by residents of towns and cities. * Rainwater harvesting – Collection and storage of rainwater from roofs or other suitable catchments. * Recycled water – Former wastewater (sewage) that has been treated and purified for reuse. * Transvasement – Building canals or redirecting rivers as massive attempts at
irrigation Irrigation is the agricultural Agriculture is the science, art and practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated Domesti ...

irrigation
in drought-prone areas.


History

Well-known historical droughts include: *1540 European drought, 1540 Central Europe, said to be the “worst drought of the millennium” with eleven months without rain and temperatures of 5–7 °C above the average of the 20th century * 1900 India killing between 250,000 and 3.25 million. * 1921–22 Soviet Union in which over 5 million perished from starvation due to drought. * 1928–30 Northwest China resulting in over 3 million deaths by famine. * 1936 and 1941 Sichuan Province China resulting in 5 million and 2.5 million deaths respectively. * The 1997–2009 2000s Australian drought, Millennium Drought in Australia led to a water supply crisis across much of the country. As a result, many desalination plants were built for the first time (List of desalination plants in Australia, see list). * In 2006, Sichuan Province China experienced its worst drought in modern times with nearly 8 million people and over 7 million cattle facing water shortages. * 12-year drought that was devastating southwest Western Australia, southeast South Australia, Victoria and northern Tasmania was "very severe and without historical precedent". * 2015–2018 Cape Town water crisis. This likelihood was tripled by climate change. The Darfur conflict in Sudan, also affecting Chad, was fueled by decades of drought; combination of drought,
desertification Desertification is a type of land degradation Land degradation is a process in which the value of the biophysical environment is affected by a combination of human-induced processes acting upon the land. It is viewed as any change or distu ...
and Human overpopulation, overpopulation are among the causes of the Darfur conflict, because the Arab Baggara nomads searching for water have to take their livestock further south, to land mainly occupied by non-Arab farming people. Approximately 2.4 billion people live in the drainage basin of the Himalayan rivers. India, China, Pakistan, Bangladesh, Nepal and Myanmar could experience floods followed by droughts in coming decades. Drought in India affecting the Ganges is of particular concern, as it provides drinking water and agricultural
irrigation Irrigation is the agricultural Agriculture is the science, art and practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated Domesti ...

irrigation
for more than 500 million people. The west coast of North America, which gets much of its water from glaciers in mountain ranges such as the Rocky Mountains and Sierra Nevada (U.S.), Sierra Nevada, also would be affected. In 2005, parts of the Amazon basin experienced the worst drought in 100 years. A 23 July 2006 article reported Woods Hole Research Center results showing that the forest in its present form could survive only three years of drought. Scientists at the Brazilian National Institute of Amazonian Research argue in the article that this drought response, coupled with the effects of
deforestation deforestation in 1750-2004 (net loss) showing anthropogenic modification of remaining forest. File:MODIS (2020-08-01).jpg, 300px, Dry seasons, exacerbated by climate change, and the use of slash-and-burn methods for clearing tropical forest ...

deforestation
on regional climate, are pushing the rainforest towards a "tipping point (climatology), tipping point" where it would irreversibly start to die. It concludes that the rainforest is on the brink of being turned into savanna or desert, with catastrophic consequences for the world's climate. According to the World Wide Fund for Nature, WWF, the combination of
climate change Contemporary climate change includes both the global warming caused by humans, and its impacts on Earth's weather patterns. There have been previous periods of climate change, but the current changes are more rapid than any known even ...
and deforestation increases the drying effect of dead trees that fuels forest fires. By far the largest part of Australia is Deserts of Australia, desert or semi-arid lands commonly known as the outback. A 2005 study by Australian and American researchers investigated the desertification of the interior, and suggested that one explanation was related to human settlers who arrived about 50,000 years ago. Regular burning by these settlers could have prevented monsoons from reaching interior Australia. In June 2008 it became known that an expert panel had warned of long term, maybe irreversible, severe ecological damage for the whole Murray-Darling basin if it did not receive sufficient water by October 2008. Australia could experience more severe droughts and they could become more frequent in the future, a government-commissioned report said on July 6, 2008. Australian environmentalist Tim Flannery, predicted that unless it made drastic changes, Perth, Western Australia, Perth in Western Australia could become the world's first ghost town, ghost metropolis, an abandoned city with no more water to sustain its population. The long Australian 2000s Australian drought, Millennial drought broke in 2010. Recurring droughts leading to
desertification Desertification is a type of land degradation Land degradation is a process in which the value of the biophysical environment is affected by a combination of human-induced processes acting upon the land. It is viewed as any change or distu ...
in East Africa have created grave ecological catastrophes, prompting food shortages in 1983–85 famine in Ethiopia, 1984–85, 2006 Horn of Africa food crisis, 2006 and 2011 East Africa drought, 2011.Sara Pantuliano and Sara Pavanello (2004
Taking drought into account Addressing chronic vulnerability among pastoralists in the Horn of Africa
Overseas Development Institute
During the 2011 drought, an estimated 50,000 to 150,000 people were reported to have died, though these figures and the extent of the crisis are disputed. In February 2012, the UN announced that the crisis was over due to a scaling up of relief efforts and a bumper harvest. Aid agencies subsequently shifted their emphasis to recovery efforts, including digging irrigation canals and distributing plant seeds. In 2012, a severe 2012 Sahel drought, drought struck the western Sahel. The Methodist Relief & Development Fund (MRDF) reported that more than 10 million people in the region were at risk of famine due to a month-long heat wave that was hovering over Niger, Mali, Mauritania and Burkina Faso. A fund of about £20,000 was distributed to the drought-hit countries. A 2021 study has found that the rise of compound warm-season droughts in Europe is a dynamic, developing phenomenon.


See also


References


External links


GIDMaPS
Global Integrated Drought Monitoring and Prediction System, University of California, Irvine

from FAO Water (Food and Agriculture Organization of the United Nations)
Global Real-Time Drought Media Monitoring
{{Authority control Droughts, Meteorological phenomena Civil defense Climate variability and change Hydrology Water and the environment Weather hazards Articles containing video clips Natural disasters