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A drought or drouth is an event of prolonged shortages in the water supply, whether atmospheric (below-average precipitation), surface water or ground water. 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 and agriculture of the affected region and harm to the local economy. Annual dry seasons in the 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.

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

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. Some others survive dry periods as buried seeds. Semi-permanent drought produces arid biomes such as deserts and grasslands. Prolonged droughts have caused mass migrations and humanitarian crisis. Most arid ecosystems have inherently low productivity. The most prolonged drought ever in the world in recorded history occurred in the Atacama Desert in Chile (400 Years).

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, ...). 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. 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. Rituals exist to prevent or avert drought, rainmaking could go from dances to scapegoating to human sacrifices. Nowadays, those ancient practices are for the most part relegated to folklore and replaced by more rational water management.

, Mexico.]] Drought is an extended period when a region notes a deficiency in its water supply whether surface or underground water. A drought can last for months or years, or may be declared after as few as 15 days.<ref>It's a scorcher - and Ireland is officially 'in drought' Irish Independent, 2013-07-18.</ref> Generally, this occurs when a region receives consistently below average precipitation. It can have a substantial impact on the ecosystem and agriculture of the affected region. Although droughts can persist for several years, even a short, intense drought can cause significant damage<ref>Living With Drought<!-- Bot generated title --></ref> and harm to the local economy.<ref>Australian Drought and Climate Change, retrieved on June 7th 2007.</ref>

Many plant species, such as cacti, have adaptations such as 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.<ref>Keddy, P.A. 2007. Plants and Vegetation: Origins, Processes, Consequences. Cambridge University Press, Cambridge, UK. 666 p.</ref> Most arid ecosystems have inherently low productivity.

This global phenomenon has a widespread impact on agriculture. Lengthy periods of drought have long been a key trigger for mass migration and played a key role in a number of migrations and humanitarian crises in various areas around the world.

According to F. Bagouls and Henri Gaussen's definition, a month (or other period) is considered dry when the mean monthly precipitation in millimeters is equal to or lower than twice the mean monthly temperature in degrees Celsius.


dead due to drought.]] Periods of droughts can have significant environmental, agricultural, health, economic and social consequences. The effect varies 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 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 of remaining water sources. Common consequences of drought include:


Drought is a normal, recurring feature of the climate in most parts of the world. 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.<ref>BBC - Weather Centre - Features - History and Religion - Weather in the Bible - Drought and Famine<!-- Bot generated title --></ref> Hunter-gatherer migrations in 9,500 BC Chile have been linked to the phenomenon,<ref>Ancient Chile Migration Mystery Tied to Drought<!-- Bot generated title --></ref> as has the exodus of early humans out of Africa and into the rest of the world around 135,000 years ago.<ref>Drought pushed ancient African immigration </ref>

, 1936]] Modern 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 ever-increasing population densities.

Regions affected

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.<ref>Looking to water to find peace in Darfur</ref>

Approximately 2.4&nbsp;billion people live in the drainage basin of the Himalayan rivers.<ref>Big melt threatens millions, says UN</ref> 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 for more than 500&nbsp;million people.<ref>Ganges, Indus may not survive: climatologists</ref><ref>Glaciers melting at alarming speed</ref><ref>Himalaya glaciers melt unnoticed</ref> 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.<ref>Glaciers Are Melting Faster Than Expected, UN Reports</ref><ref>Water shortage worst in decades, official says, Los Angeles Times</ref>

belt during the 2012 drought.]]

In 2005, parts of the Amazon basin experienced the worst drought in 100 years.<ref>Environmental News Service - Amazon Drought Worst in 100 Years</ref><ref>Drought Threatens Amazon Basin - Extreme conditions felt for second year running</ref> 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.<ref>''Amazon rainforest 'could become a desert' '', The Independent, July 23, 2006. Retrieved September 28, 2006.</ref><ref>''Dying Forest: One year to save the Amazon'', The Independent, July 23, 2006. Retrieved September 28, 2006.</ref> 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. 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 WWF, the combination of climate change and deforestation increases the drying effect of dead trees that fuels forest fires.<ref>''Climate change a threat to Amazon rainforest, warns WWF'', World Wide Fund for Nature, March 9, 2996. Retrieved September 28, 2006.</ref>

, India in 2012.]] By far the largest part of Australia is 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.<ref>Sensitivity of the Australian Monsoon to insolation and vegetation: Implications for human impact on continental moisture balance, Geological Society of America</ref> 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.<ref>Australian rivers 'face disaster', BBC News</ref> Australia could experience more severe droughts and they could become more frequent in the future, a government-commissioned report said on July 6, 2008.<ref>Australia faces worse, more frequent droughts: study, Reuters</ref> 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.<ref>Metropolis strives to meet its thirst, BBC News</ref> The long Australian Millennial drought broke in 2010.

Recurring droughts leading to desertification in East Africa have created grave ecological catastrophes, prompting food shortages in 1984-1985, 2006 and 2011.<ref name=ODI>Sara Pantuliano and Sara Pavanello (2009) Taking drought into account Addressing chronic vulnerability among pastoralists in the Horn of Africa Overseas Development Institute</ref> During the 2011 drought, an estimated 50,000 to 150,000 people were reported to have died,<ref>“Fatal Failure: Did Aid Agencies Let Up To 100,000 Somalis Die in 2011?”. Time. January 18, 2012.</ref> though these figures and the extent of the crisis are disputed.<ref name=“Mafhscbafro”>

</ref> In February 2012, the UN announced that the crisis was over due to a scaling up of relief efforts and a bumper harvest.<ref name=“Unsfisiobrr”>U.N. Says Famine in Somalia Is Over, but Risks Remain</ref> Aid agencies subsequently shifted their emphasis to recovery efforts, including digging irrigation canals and distributing plant seeds.<ref name=“Unsfisiobrr”/>

In 2012, a severe 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.<ref></ref>


File:Ancient Dry Spells Offer Clues About the Future of Drought.ogv

Generally, rainfall is related to the amount and dew point [determined by air temperature] of water vapour carried by regional atmosphere, combined with the upward forcing of the air mass containing that water vapour. If these combined factors do not support precipitation volumes sufficient to reach the surface, the result is a drought. This can be triggered by high level of reflected sunlight, [high albedo], and above average prevalence of high pressure systems, winds carrying continental, rather than oceanic air masses (i.e. reduced water content), and ridges of high pressure areas from behaviors which prevent or restrict the developing of thunderstorm activity or rainfall over one certain region. Oceanic and atmospheric weather cycles such as the El Niño-Southern Oscillation (ENSO) make drought a regular recurring feature of the Americas along the Midwest and Australia. Guns, Germs, and Steel author Jared Diamond sees the stark impact of the multi-year ENSO cycles on Australian weather patterns as a key reason that Australian aborigines remained a hunter-gatherer society rather than adopting agriculture.<ref>Guns, Germs, and Steel by Jared Diamond 1997, pgs 308-309</ref> Another climate oscillation known as the North Atlantic Oscillation has been tied to droughts in northeast Spain.<ref>


Human activity can directly trigger exacerbating factors such as over farming, excessive irrigation,<ref name=Galilee>A biblical tragedy as Sea of Galilee faces drought Belfast Telegraph</ref> deforestation, and erosion adversely impact the ability of the land to capture and hold water.<ref>Kenya: Deforestation exacerbates droughts, floods</ref> While these tend to be relatively isolated in their scope, activities resulting in global climate change are expected to trigger droughts with a substantial impact on agriculture<ref>[[NOAA] Drought and climate change: implications for the West] December 2002</ref> throughout the world, and especially in developing nations.<ref>Record rise in wheat price prompts UN official to warn that surge in food prices may trigger social unrest in developing countries</ref><ref>Fuel costs, drought influence price increase</ref><ref>Nigerian Scholar Links Drought, Climate Change to Conflict Africa Oct, 2005</ref> Overall, global warming will result in increased world rainfall.<ref>Is Water the New Oil?</ref> Along with drought in some areas, flooding and erosion will increase in others. Paradoxically, 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.<ref name=“NewScientist”>''Sunshade' for global warming could cause drought'' 2 August 2007 New Scientist, Catherine Brahic</ref>


stranded by the retreat of the Aral Sea.]] As a drought persists, the conditions surrounding it gradually worsen and its impact on the local population gradually increases. People tend to define droughts in three main ways:<ref>[[NOAA] factsheet], retrieved April 10, 2007</ref>

  1. Meteorological drought is brought about when there is a prolonged period with less than average precipitation. Meteorological drought usually precedes the other kinds of drought.
  2. Agricultural droughts are droughts that affect crop production or the ecology of the range. This condition can also arise independently from any change in precipitation levels when 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.
  3. Hydrological drought is brought about when the water reserves available in sources such as aquifers, lakes and reservoirs fall below the statistical average. 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, Kazakhstan was recently 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.<ref>BBC article on the World Bank loan to save the Aral Sea</ref> Similar circumstances also place their largest lake, Balkhash, at risk of completely drying out.<ref>BBC article from 2004 concerning the risk of Kazakhstan losing the lake</ref>

Protection and relief

during El Niño.]] 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.<ref>Cloud seeding helps alleviate drought<!-- Bot generated title --></ref>
  • Desalination - 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.<ref>BBC's From Our Own Correspondent on khat water usage</ref> Careful monitoring of moisture levels can also help predict increased risk for wildfires, using such metrics as the Keetch-Byram Drought Index<ref name=“autogenerated1” /> or Palmer Drought Index.
  • Land use - Carefully planned crop rotation can help to minimize 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.
  • 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 in drought-prone areas.

drought. The aerosol scale (yellow to dark reddish-brown) indicates the relative amount of particles that absorb sunlight.]]

Dry areas

<gallery widths=“220” heights=“160”> File:Huntington Desert Garden Cactus (etc).jpg|Succulent plants are well-adapted to survive long periods of drought. File:Fields outside benambra.jpg|Fields outside Benambra, Victoria, Australia suffering from drought conditions. File:ShrinkingLakeChad-1973-1997-EO.jpg|Lake Chad in a 2001 satellite image. The lake has shrunk by 95% since the 1960s.<ref>Disappearing Lakes, Shrinking Seas</ref><ref>Shrinking African Lake Offers Lesson on Finite Resources</ref> File:Sheep on a drought-affected paddock.jpg|Sheep on a drought affected paddock near Uranquinty, New South Wales. </gallery>

See also


Basic meteorological concepts and phenomena Civil defense Climatology * Hydrology Natural disasters Water and the environment Weather hazards

A drought is a period of low or no rain fall or a deficiency in other water sources that leads to insufficient water supply for the needs of a given area. A drought can happen almost anywhere, but some places experience them more often than others.


Understanding Droughts

Droughts may be caused by natural climate change (e.g. El Niño-Southern Oscillation (ENSO) in the Pacific) or by man-made factors (e.g. deforestation in Haiti). In rural areas droughts are especially damaging while in urban areas droughts barely make an impact on daily life.

Preparing for a Drought

Preparing for a drought is similar to most other disasters; store food and water with emphasis on water, but also reduce your need for water for non-essential purposes such as watering lawns and washing cars. Using a car wash with recycled water will assist in the latter point. Alternative gardening practices such as use of a hot house, drip watering system or other measures can save water as well.


Food should always be stored, and a drought is no exception. Droughts often cause food shortages in undeveloped countries or even in developed countries if the drought covers a large enough agricultural area even if you are not directly affected by the drought. Fortunately most developed countries are able to support an area suffering from drought with sufficient food supplements for the duration of the emergency. However this comes at a price to the consumer so store food during times when food is plentiful (and cheaper) for use during droughts.

Water Reserves

Water should always be stored, but for a drought sufficient water storage is critical. If you live in an area that is particularly subject to drought you should store far more water than you would in an area less subject to drought. Even if you live over an aquifer and you have a well consider storing water in a pond for your livestock and in tank or cistern for yourself. Water tables drop during a prolonged drought or when they are tapped by communities as alternatives to low reservoirs. If you live in an urban setting store water in appropriate tanks since zoning laws will likely prohibit building a cistern or drilling your own well.

Water Usage Reduction

Reducing your need of water is extremely important in preparing for a drought. It is easy to take for granted the enormous amount of water that we use throughout the day, water is used for consumption, food preparation, sanitation, and gardening. The need for water consumption cannot be reduced, but the amount used for food can be. You should avoid storing foods that require you to boil water and then discard the water after use. Sanitation is one of the easiest areas to reduce water consumption, showers, toilet flushes, baths, and brushing your teeth all consume water. Replacing your shower head with a low-flow unit, using low volume toilet(or you can put some bricks in a regular toilet tank), and never leave the water running while you brush your teeth. Gardening uses a lot of water, especially when rain isn't falling. If you live where droughts are common, then you should stick to plants with low water requirements.

Living during a Drought

Living during a drought is mostly about conserving water and implementing your previous preparations. You should shorten your showers, and take sponge baths when possible. Stop preparing food that waste water during preparation, and use any left over cooking water in your garden or for pets and livestock.

Drought Aftermath

Most areas will recover from a drought within one harvest rotation, but often the wild plant and wild life can be devasated. Many older shut-ins or unprepared individuals may not survive if the drought is severe enough.

See Also


External Links

drought.txt · Last modified: 2020/03/12 18:33 (external edit)