Drought

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For other uses, see Drought (disambiguation). Drought_sentence_0

A drought is an event of prolonged shortages in the water supply, whether atmospheric (below-average precipitation), surface water or ground water. Drought_sentence_1

A drought can last for months or years, or may be declared after as few as 15 days. Drought_sentence_2

It can have a substantial impact on the ecosystem and agriculture of the affected region and harm to the local economy. Drought_sentence_3

Annual dry seasons in the tropics significantly increase the chances of a drought developing and subsequent bush fires. Drought_sentence_4

Periods of heat can significantly worsen drought conditions by hastening evaporation of water vapour. Drought_sentence_5

Drought is a recurring feature of the climate in most parts of the world. Drought_sentence_6

However, these regular droughts have become more extreme and more unpredictable due to climate change. Drought_sentence_7

In fact studies based on dendrochronology, or tree rings dating, confirm that drought affected by global warming goes back to 1900. Drought_sentence_8

Many plant species, such as those in the family Cactaceae (or cacti), have drought tolerance adaptations like reduced leaf area and waxy cuticles to enhance their ability to tolerate drought. Drought_sentence_9

Some others survive dry periods as buried seeds. Drought_sentence_10

Semi-permanent drought produces arid biomes such as deserts and grasslands. Drought_sentence_11

Prolonged droughts have caused mass migrations and humanitarian crisis. Drought_sentence_12

Most arid ecosystems have inherently low productivity. Drought_sentence_13

The most prolonged drought ever in the world in recorded history occurred in the Atacama Desert in Chile (400 Years). Drought_sentence_14

Drought affect food production and human society, so they are considered a disaster, of natural, supernatural or human cause (which itself could be supernatural causes, malediction, sin, ...). Drought_sentence_15

It is among the earliest documented climatic events, present in the Epic of Gilgamesh and tied to the Biblical story of Joseph's arrival in and the later Exodus from Ancient Egypt. Drought_sentence_16

Hunter-gatherer migrations in 9,500 BC Chile have been linked to the phenomenon, as has the exodus of early humans out of Africa and into the rest of the world around 135,000 years ago. Drought_sentence_17

Rituals exist to prevent or avert drought, rainmaking could go from dances to scapegoating to human sacrifices. Drought_sentence_18

Nowadays, those ancient practices are for the most part relegated to folklore and replaced by more rational water management. Drought_sentence_19

Types of drought Drought_section_0

People tend to define droughts in three main ways: Drought_sentence_20

Drought_ordered_list_0

  1. Meteorological drought occurs when there is a prolonged time with less than average precipitation. Meteorological drought usually precedes the other kinds of drought.Drought_item_0_0
  2. 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 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.Drought_item_0_1
  3. 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. For instance, around 2007 Kazakhstan was awarded 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. Similar circumstances also place their largest lake, Balkhash, at risk of completely drying out.Drought_item_0_2

As a drought persists, the conditions surrounding it gradually worsen and its impact on the local population gradually increases. Drought_sentence_21

Causes of drought Drought_section_1

Precipitation deficiency Drought_section_2

See also: Precipitation Drought_sentence_22

Mechanisms of producing precipitation include convective, stratiform, and orographic rainfall. Drought_sentence_23

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. Drought_sentence_24

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. Drought_sentence_25

Droughts occur mainly in areas where normal levels of rainfall are, in themselves, low. Drought_sentence_26

If these factors do not support precipitation volumes sufficiently to reach the surface over a sufficient time, the result is a drought. Drought_sentence_27

Drought 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, and ridges of high pressure areas aloft can prevent or restrict the developing of thunderstorm activity or rainfall over one certain region. Drought_sentence_28

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. Drought_sentence_29

Dry season Drought_section_3

See also: Dry season Drought_sentence_30

Within the tropics, distinct, wet and dry seasons emerge due to the movement of the Intertropical Convergence Zone or Monsoon trough. Drought_sentence_31

The dry season greatly increases drought occurrence, and is characterized by its low humidity, with watering holes and rivers drying up. Drought_sentence_32

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. Drought_sentence_33

Examples of such animals are zebras, elephants, and wildebeest. Drought_sentence_34

Because of the lack of water in the plants, bushfires are common. Drought_sentence_35

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). Drought_sentence_36

Periods of warmth quicken the pace of fruit and vegetable production, increase evaporation and transpiration from plants, and worsen drought conditions. Drought_sentence_37

El Niño Drought_section_4

See also: El Niño Drought_sentence_38

Drier and hotter weather occurs in parts of the Amazon River Basin, Colombia, and Central America during El Niño events. Drought_sentence_39

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. Drought_sentence_40

Conditions are also drier than normal from December to February in south-central Africa, mainly in Zambia, Zimbabwe, Mozambique, and Botswana. Drought_sentence_41

Direct effects of El Niño resulting in drier conditions occur in parts of Southeast Asia and Northern Australia, increasing bush fires, worsening haze, and decreasing air quality dramatically. Drought_sentence_42

Drier-than-normal conditions are also in general observed in Queensland, inland Victoria, inland New South Wales, and eastern Tasmania from June to August. Drought_sentence_43

As warm water spreads from the west Pacific and the Indian Ocean to the east Pacific, it causes extensive drought in the western Pacific. Drought_sentence_44

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. Drought_sentence_45

The years 1968 and 2005 had the next driest Februaries, when 8.4 mm of rain fell. Drought_sentence_46

Erosion and human activities Drought_section_5

See also: Aeolian processes Drought_sentence_47

Human activity can directly trigger exacerbating factors such as over farming, excessive irrigation, deforestation, and erosion adversely impact the ability of the land to capture and hold water. Drought_sentence_48

In arid climates, the main source of erosion is wind. Drought_sentence_49

Erosion can be the result of material movement by the wind. Drought_sentence_50

The wind can cause small particles to be lifted and therefore moved to another region (deflation). Drought_sentence_51

Suspended particles within the wind may impact on solid objects causing erosion by abrasion (ecological succession). Drought_sentence_52

Wind erosion generally occurs in areas with little or no vegetation, often in areas where there is insufficient rainfall to support vegetation. Drought_sentence_53

Loess is a homogeneous, typically nonstratified, porous, friable, slightly coherent, often calcareous, fine-grained, silty, pale yellow or buff, windblown (Aeolian) sediment. Drought_sentence_54

It generally occurs as a widespread blanket deposit that covers areas of hundreds of square kilometers and tens of meters thick. Drought_sentence_55

Loess often stands in either steep or vertical faces. Drought_sentence_56

Loess tends to develop into highly rich soils. Drought_sentence_57

Under appropriate climatic conditions, areas with loess are among the most agriculturally productive in the world. Drought_sentence_58

Loess deposits are geologically unstable by nature, and will erode very readily. Drought_sentence_59

Therefore, windbreaks (such as big trees and bushes) are often planted by farmers to reduce the wind erosion of loess. Drought_sentence_60

Wind erosion is much more severe in arid areas and during times of drought. Drought_sentence_61

For example, in the Great Plains, 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. Drought_sentence_62

Climatic changes Drought_section_6

See also: Climate change Drought_sentence_63

Overall, global warming will result in increased world rainfall. Drought_sentence_64

Activities resulting in global climate change are expected to trigger droughts with a substantial impact on agriculture throughout the world, and especially in developing nations. Drought_sentence_65

Along with drought in some areas, flooding and erosion could increase in others. Drought_sentence_66

Some proposed solutions to global warming that focus on more active techniques, solar radiation management through the use of a space sunshade for one, may also carry with them increased chances of drought. Drought_sentence_67

According to the Special Report on Climate Change and Land of the Intergovernmental Panel on Climate Change climate change increase drought and desertification. Drought_sentence_68

Hundreds of million people are affected. Drought_sentence_69

The affected area includes large territories in Africa, Asia, Australia, and South America. Drought_sentence_70

Consequences of drought Drought_section_7

One can divide the effects of droughts and water shortages into three groups: environmental, economic and social. Drought_sentence_71

Drought_unordered_list_1

  • 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, worse health of trees and the appearance of pests and dendroid diseases.Drought_item_1_3
  • 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.Drought_item_1_4
  • 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.Drought_item_1_5

Effects vary according to vulnerability. Drought_sentence_72

For example, subsistence farmers are more likely to migrate during drought because they do not have alternative food-sources. Drought_sentence_73

Areas with populations that depend on water sources as a major food-source are more vulnerable to famine. Drought_sentence_74

Drought can also reduce water quality, because lower water-flows reduce dilution of pollutants and increase contamination of remaining water-sources. Drought_sentence_75

Common consequences of drought include: Drought_sentence_76

Drought_unordered_list_2

Historical droughts Drought_section_8

Examples Drought_section_9

Main article: List of droughts Drought_sentence_77

Well-known historical droughts include: Drought_sentence_78

Drought_unordered_list_3

  • 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 centuryDrought_item_3_22
  • 1900 India killing between 250,000 and 3.25 million.Drought_item_3_23
  • 1921–22 Soviet Union in which over 5 million perished from starvation due to drought.Drought_item_3_24
  • 1928–30 Northwest China resulting in over 3 million deaths by famine.Drought_item_3_25
  • 1936 and 1941 Sichuan Province China resulting in 5 million and 2.5 million deaths respectively.Drought_item_3_26
  • The 1997–2009 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 (see list).Drought_item_3_27
  • 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.Drought_item_3_28
  • 12-year drought that was devastating southwest Western Australia, southeast South Australia, Victoria and northern Tasmania was "very severe and without historical precedent".Drought_item_3_29
  • 2015–2018 Cape Town water crisis. This likelihood was tripled by climate change.Drought_item_3_30

The Darfur conflict in Sudan, also affecting Chad, was fueled by decades of drought; combination of drought, desertification and 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. Drought_sentence_79

Approximately 2.4 billion people live in the drainage basin of the Himalayan rivers. Drought_sentence_80

India, China, Pakistan, Bangladesh, Nepal and Myanmar could experience floods followed by droughts in coming decades. Drought_sentence_81

Drought in India affecting the Ganges is of particular concern, as it provides drinking water and agricultural irrigation for more than 500 million people. Drought_sentence_82

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, also would be affected. Drought_sentence_83

In 2005, parts of the Amazon basin experienced the worst drought in 100 years. Drought_sentence_84

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. Drought_sentence_85

Scientists at the Brazilian National Institute of Amazonian Research argue in the article that this drought response, coupled with the effects of deforestation on regional climate, are pushing the rainforest towards a "tipping point" where it would irreversibly start to die. Drought_sentence_86

It concludes that the rainforest is on the brink of being turned into savanna or desert, with catastrophic consequences for the world's climate. Drought_sentence_87

According to the WWF, the combination of climate change and deforestation increases the drying effect of dead trees that fuels forest fires. Drought_sentence_88

By far the largest part of Australia is desert or semi-arid lands commonly known as the outback. Drought_sentence_89

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. Drought_sentence_90

Regular burning by these settlers could have prevented monsoons from reaching interior Australia. Drought_sentence_91

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. Drought_sentence_92

Australia could experience more severe droughts and they could become more frequent in the future, a government-commissioned report said on July 6, 2008. Drought_sentence_93

Australian environmentalist Tim Flannery, predicted that unless it made drastic changes, Perth in Western Australia could become the world's first ghost metropolis, an abandoned city with no more water to sustain its population. Drought_sentence_94

The long Australian Millennial drought broke in 2010. Drought_sentence_95

Recurring droughts leading to desertification in East Africa have created grave ecological catastrophes, prompting food shortages in 1984–85, 2006 and 2011. Drought_sentence_96

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. Drought_sentence_97

In February 2012, the UN announced that the crisis was over due to a scaling up of relief efforts and a bumper harvest. Drought_sentence_98

Aid agencies subsequently shifted their emphasis to recovery efforts, including digging irrigation canals and distributing plant seeds. Drought_sentence_99

In 2012, a severe drought struck the western Sahel. Drought_sentence_100

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. Drought_sentence_101

A fund of about £20,000 was distributed to the drought-hit countries. Drought_sentence_102

Protection, mitigation and relief Drought_section_10

Agriculturally, people can effectively mitigate much of the impact of drought through irrigation and crop rotation. Drought_sentence_103

Failure to develop adequate drought mitigation strategies carries a grave human cost in the modern era, exacerbated by ever-increasing population densities. Drought_sentence_104

President Roosevelt on April 27, 1935, signed documents creating the Soil Conservation Service (SCS)—now the Natural Resources Conservation Service (NRCS). Drought_sentence_105

Models of the law were sent to each state where they were enacted. Drought_sentence_106

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. Drought_sentence_107

It was not until the 1950s that there was an importance placed on water conservation was put into the existing laws (NRCS 2014). Drought_sentence_108

Strategies for drought protection, mitigation or relief include: Drought_sentence_109

Drought_unordered_list_4

  • Dams – many dams and their associated reservoirs supply additional water in times of drought.Drought_item_4_31
  • Cloud seeding – a form of intentional weather modification to induce rainfall. This remains a hotly debated topic, as the 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.Drought_item_4_32
  • Desalination – use of sea water for irrigation or consumption.Drought_item_4_33
  • 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.Drought_item_4_34
  • Land use – Carefully planned crop rotation can help to minimize erosion and allow farmers to plant less water-dependent crops in drier years.Drought_item_4_35
  • 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.Drought_item_4_36
  • Rainwater harvesting – Collection and storage of rainwater from roofs or other suitable catchments.Drought_item_4_37
  • Recycled water – Former wastewater (sewage) that has been treated and purified for reuse.Drought_item_4_38
  • Transvasement – Building canals or redirecting rivers as massive attempts at irrigation in drought-prone areas.Drought_item_4_39

See also Drought_section_11

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Drought.