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Drought

Drought

TYPES OF DROUGHT

COPING WITH DROUGHT

MAJOR DROUGHT EVENTS

BIBLIOGRAPHY

Drought is a feature of climate that is defined as a period of below-average rainfall sufficiently long and intense to result in serious environmental and socioeconomic stresses, such as crop failures and water shortages, in the affected area. Droughts can occur in any climatic region, but their characteristics vary considerably among regions. What droughts in all climatic regions have in common is their gradual onset, whichin contrast to other natural hazardsmakes their beginning and end difficult to identify. Defined primarily as natural phenomena, droughts have not received much attention in the social sciences. Only since the 1990s, with the increasing appreciation of the linkages between the environment and society, have droughts begun to be viewed as an issue of interest also for the social sciences.

Drought is caused by the sinking motion of air in a high-pressure cell, which results in decreasing relative humidity of the air and little or no precipitation. Most climatic regions are temporarily under the influence of high pressure; droughts occur only when atmospheric circulation patterns that cause the high pressure persist or recur persistently over an unusually long period of time. Because of the global nature of atmospheric circulation, explanations for anomalous circulation patterns extend far beyond the drought-affected area. Thus global patterns of atmospheric pressure systems and sea surface temperatures have been invoked to explain the occurrence of periodically recurring drought events in some parts of the globe. Most prominent among those global patterns is the El Niño Southern Oscillation (ENSO), a coupled ocean-atmosphere anomaly that originates in the Pacific basin but has repercussions on the climatic conditions in areas as far apart as southern Africa, India, and Brazil. Anthropogenic processes that lead to changes in land cover, such as deforestation and overgrazing, affect local-scale moisture recycling and can induce local reductions in rainfall. Although simulation models have shown the possibility of substantial reductions in rainfall resulting from land-cover change, anthropogenic disturbances large enough to explain more than local-scale reductions in rainfall have not been observed.

TYPES OF DROUGHT

The effects of drought on environment, economy, and society are manifold. In order of the increasing severity and scope of their impacts, four types of drought are commonly distinguished: A meteorological drought manifests itself in a shortfall of precipitation or changes in precipitation intensity and timing, possibly aggravated by other climatic factors, such as high temperatures and winds. Risks associated with this type of drought include wildfire hazard and reduced water infiltration into the soil. If the drought persists long enough to result in significant soil water deficits and plant water stress, it crosses the threshold into an agricultural drought. Lower crop yields and quality, as well as increased soil erosion and dust emission, are possible impacts expected from this type of drought.

Because various crops differ in their water demand, a farmers choice of crop type can either buffer or exacerbate the effects of an agricultural drought. A drought is classified as a hydrological drought once the precipitation shortfall affects surface and subsurface water supplies. Hydrological droughts usually lag behind the occurrence of meteorological droughts because of the time needed for precipitation deficits to reach the surface and groundwater levels of the water cycle. Their impacts, which consequently are also out of phase with those of a meteorological and agricultural drought, include reduced stream flow, below-normal reservoir and lake levels, loss of wetlands, and declining water quality. Although climate is the primary factor of a hydrological drought, humans contribute to its effects by changes in land and water use, such as urbanization and the construction of dams. Finally, a socioeconomic drought occurs when the supply of economic goods and services, including water, forage, food, and hydroelectric power, can no longer be met for drought-related causes. Farmers and ranchers, who depend on agricultural and pasture productivity, are the first to suffer losses. Then follow industries depending on agricultural production. As a result, consumers may have to pay more for their food and other weather-sensitive products and services.

The socioeconomic effects of a drought vary not only in proportion to the severity of the climatological event but also depending on the vulnerability of the affected population. Monetary costs arise for any economy hit by drought, such as to cover for lost crops, crop insurance payouts, and fire damage; but only in the most vulnerable populations of the developing world are drought effectsfood insecurity, famine, health problems, and loss of life and livelihoodsoften paired with economic, social, and political difficulties. Subsistence farmers and pastoralists in particular suffer from crop and livestock losses, as well as from increased food prices. Droughts force many of them to migrate from rural to urban areas, increasing pressure on resources there.

COPING WITH DROUGHT

Scientists and decision-makers have devised a number of ways to deal with drought, which can be grouped into drought monitoring, forecasting, and mitigation. Meteorologists around the world carefully monitor meteorological and hydrological variables (precipitation patterns, soil moisture, stream flow) over time to determine the onset and end of a drought. Satellite remote sensing technology has contributed immensely to quantitative monitoring over large geographic areas. Understanding the complex physical aspects leading to droughts is a prerequisite for making increasingly reliable and credible drought predictions. Empirical studies have shown that drought results from a complex interplay of different climatological factors, which makes forecasting difficult. In the tropics, where scientists have made significant advances in understanding the climate system, the potential for seasonal drought predictions is promising, particularly with respect to droughts related to ENSO. Multiyear droughts as well as droughts outside the tropics still cannot be predicted with a level of accuracy that is without risk for the users of those predictions. Knowing the frequency, duration, and spatial extent of past droughts, however, helps in determining the likelihood and potential severity of future droughts.

In addition to the assessment of meteorological processes, drought mitigation also requires an understanding of the vulnerabilities of different population groups to drought. Mitigation tools range from early warning systems, which monitor both meteorological conditions and vulnerable populations (e.g., the Famine Early Warning Systems Network, operating in Africa, Central America, and Afghanistan), to various forms of weather-related crop insurance schemes (e.g., in the United States and Australia among others), emergency water supply augmentation (e.g., tapping new water resources), and water demand reduction (e.g., by means of economic incentives for water conservation, improvement of water use efficiencies, breeding for drought tolerance, diversification to less weather-dependent economic activities, and public water conservation awareness programs). As droughts are expected to become more frequent and more extreme with global warming, it is imperative to improve drought mitigation efforts and increase future drought preparedness.

MAJOR DROUGHT EVENTS

Major drought events in modern history include:

  • China, 18771878: Provinces across northern China were depopulated as grain stocks ran out as a result of severe droughts. Millions of people perished from starvation.
  • Soviet Union, 19211922: A fierce drought hit the Ukraine and Volga regions. The death toll reached almost five million people, more than the total number of casualties in World War I (19141918).
  • United States, 1930s: The Dust Bowl drought, which ravaged the American and Canadian Great Plains in the 1930s, is considered one of the major droughts of the twentieth century. Coinciding with the Great Depression, it had major impacts on the United States and Canada, including a mass migration from the Great Plains to the western coast in search of better living conditions.
  • West Africa, 1970s: The West African Sahel region experienced droughts of unprecedented spatial extent and duration, which created a famine that killed a million people and affected the livelihoods of more than fifty million. The great Sahelian droughts were also blamed for widespread environmental degradation of this dryland region.
  • Ethiopia, 19841985: A severe drought, exacerbated by the governments censorship of news of the emerging crisis, brought about famine and forced millions to leave their homes, triggering the worlds worst refugee crisis to date.

In 2005 Australia experienced a major drought coupled with above-average temperatures, with the southern agricultural areas particularly hard hit. In 2006 drought conditions prevailed across much of Europefor Spain the most serious drought in more than a centuryand caused water shortages for agricultural and tourism sectors. At the same time, China faced its worst drought in fifty years, with crop failures and deaths of cattle causing huge economic losses.

SEE ALSO Agricultural Industry; Disaster Management; Famine; Food; Human Ecology; Irrigation; Natural Disasters; Water Resources

BIBLIOGRAPHY

Glantz, Michael H., ed. 1987. Drought and Hunger in Africa: Denying Famine a Future. Cambridge, U.K., and New York: Cambridge University Press.

Glantz, Michael H., ed. 1994. Drought Follows the Plow: Cultivating Marginal Areas. Cambridge, U.K., and New York: Cambridge University Press.

Kogan, Felix. 1997. Global Drought Watch from Space. Bulletin of the American Meteorological Society 78 (4): 621636.

National Drought Mitigation Center. University of NebraskaLincoln. http://www.drought.unl.edu.

Vogt, Jürgen V., and Francesca Somma, eds. 2000. Drought and Drought Mitigation in Europe. Dordrecht and Boston: Kluwer Academic Publishers.

Wilhite, Donald A., ed. 2000. Drought: A Global Assessment. London and New York: Routledge.

Wilhite, Donald A., ed. 2005. Drought and Water Crises: Science, Technology, and Management Issues. Boca Raton: Taylor and Francis.

Stefanie M. Herrmann

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Drought

Drought

Drought is an extended period of exceptionally low precipitation. A drought can feature additional weather characteristics, including high temperatures and high winds.

Although low precipitation (rain, snow, or sleet) marks both droughts and deserts, the two are different. A desert is a region that experiences low precipitation as an everyday occurrence. A drought, on the other hand, is a temporary condition in which precipitation is abnormally low for a particular region. Droughts may occur at any time in any part of the world and last anywhere from days to weeks to decades.

The U.S. National Weather Service recognizes three categories of drought. A dry spell occurs when there is less than .03 inch (.08 centimeter) of rainfall during a minimum of 15 consecutive days. A partial drought occurs when the average daily rainfall does not exceed .008 inch (.02 centimeter) during a 29-day period. An absolute drought occurs when there is no measurable rainfall over a period of at least 15 days.

The intensity of a drought may be measured by the ability of living things in the affected area to tolerate the dry conditions. Some plants quickly fall prey to droughts while others, such as cacti and mesquite trees, survive dry conditions by either storing water in their tissues or by going dormant (a state in which growth activity stops). Although a drought may end abruptly with the return of adequate rainfall, the effects of a drought on the landscape and its inhabitants may last for years.

History

Droughts have taken place around the world throughout history. Some scientist theorize that droughts brought about the migrations of early humans. From 1876 to 1879, severe droughts in China caused the deaths of millions of people from lack of food. In 1921, a drought along the Volga River basin in Russia led to the deaths of almost five million people, more than the total number of deaths in World War I (191418).

The best-known American drought occurred on the Great Plains region during the mid-1930s. Labeled the Dust Bowl, the affected area covered almost 50 million acres in parts of Colorado, New Mexico, Kansas, Texas, and Oklahoma. During this period, dust storms destroyed crops and buried agricultural fields with drifting sand and dust. As depicted by American writer John Steinbeck in his award-winning novel The Grapes of Wrath, many farm families had to abandon their land.

Drought and famine have severely affected areas throughout Africa. Beginning in the late 1960s, in the Sahel region south of the Sahara Desert in northern Africa, a prolonged drought contributed to the deaths of an estimated 100,000 people. The region was struck again by drought in the mid-1980s and early 1990s. War and drought in Ethiopia in the early 1980s brought about the starvation of an estimate one million people and the forced migration of hundreds of thousands of others.

Drought combined with social unrest continued to afflict many countries at the beginning of the twenty-first century. The African nations of Djibouti, Eritrea, Ethiopia, Kenya, Somalia, and Sudan were all hit hard by a massive drought that began in the late 1990s. Conflicts like the

border war between Eritrea and Ethiopia slowed the delivery of famine aid. Devastating civil wars also worsened the effect of drought in the countries of Afghanistan and Tajikistan. The unrelenting droughts were the worst those countries had seen in decades.

The El Niño weather phenomenon typically brings about droughts in various parts of the world as it disrupts normal weather patterns. Perhaps one of the worst such droughts occurred in Southeast Asia as a result of the 199798 El Niño period. The monsoon rains that normally drench the area each September were delayed. Consequently, the jungle fires set by farmers to clear land were not damped by the usual rain, but instead raged out of control, propelled by hot winds. The smoke from the fires hung over Southeast Asia like a thick, dirty blanket. It quickly became the worst pollution crisis in world history. At least 1,000 people died from breathing the toxic air; several hundred thousand more were sickened.

Human impact on droughts

Soil that lacks humus (nutrient-rich material resulting from decaying plants) and the binding property of plant roots cannot absorb or retain moisture properly. Dry, crusty soil is easily moved by winds. The overgrazing of farm animals, the overcultivation of farmland, and the clear-cutting of forests all contribute to such soil conditions, adding to the severity of droughts.

[See also Erosion; Hydrologic cycle ]

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Drought

Drought

Drought is a temporary hazard of nature occurring from a lack of precipitation over an extended period of time. Drought differs from aridity, a permanent feature of climate restricted to regions of low rainfall. Rainfall deficiencies caused by a drought create a severe hydrologic imbalance resulting in considerable water shortages.

The beginning of a drought is typically determined by comparing the current meteorological situation to an average based on a 30-year period of record. This "operational" definition of drought allows meteorologists to analyze the frequency, severity, and duration of the aberration for any given historical period and aides in the development of response and mitigation strategies.

Characteristics of drought are highly variable from region to region, depending on atmospheric factors such as temperature , wind , relative humidity , and amount of sunshine and cloud cover. High temperatures and lots of sunshine can increase evaporation and transpiration to such an extreme that frequent rainfall is incapable of restoring the loss. Meteorological definitions of drought, therefore, may deviate from operational definitions and are usually based on the length of the dry period and the degree of dryness in comparison to the daily average.

Drought is more than a physical phenomena; an extended period of dryness can have a significant socioeconomic impact. Drought presents the most serious physical hazard to crops in nearly all regions of the world. The agricultural sector is usually the first to be affected by dryness, since crops are heavily dependent on stored soil water. In addition to a decline in agricultural products, a shortfall in the water supply can disrupt availability of other economic goods such as hydroelectric power. The 198889 Uruguay drought resulted in a significant decline of hydroelectric power because the dryness disrupted the streamflows needed for production.

See also Hydrologic cycle

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drought

drought, abnormally long period of insufficient rainfall. Drought cannot be defined in terms of inches of rainfall or number of days without rain, since it is determined by such variable factors as the distribution in time and area of precipitation during and before the dry period. Since ancient times droughts have had far-reaching effects on humankind by causing the failure of crops, decreasing natural vegetation, and depleting water supplies. Livestock and wildlife, as well as humans, die of thirst and famine; large land areas often suffer damage from dust storms or fire. Drought is thought by some to have caused migrations of early humans. In India and China drought has periodically brought widespread privation and death. In 1930 lack of rainfall devastated the Great Plains of the United States; called the Dust Bowl, its area spread to alarming dimensions (about 50 million acres). During 1962 much of the eastern part of the United States experienced the worst drought in more than 50 years. Some two thirds of the United States experienced drought that combined with some of warmest temperatures on record in the summer of 2012. Since the 1960s severe, sometimes recurring droughts have afflicted countries in many parts of Africa. Clearcutting of trees for firewood, overgrazing, and overcultivation, which lead to land degredation, contribute to this drought cycle.

See C. S. Russell et al., Drought and Water Supply (1970); W. C. Palmer and L. M. Denny, Drought Bibliography (1971); R. V. Garcia and J. Escudero, Drought and Man (1986).

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drought

drought / drout/ • n. a prolonged period of abnormally low rainfall; a shortage of water resulting from this. ∎  fig. a prolonged absence of something specified: he ended a five-game hitting drought. ∎ archaic thirst. DERIVATIVES: drought·i·ness n. drought·y adj.

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drought

drought A relative term denoting a period during which rainfall is either totally absent or substantially lower than usual for the area in question, so that there is a resulting shortage of water for human use, agriculture, or natural vegetation and fauna.

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drought

drought A period during which rainfall is either totally absent or substantially lower than usual for the area in question, so that there is a resulting shortage of water for human use, agriculture, or natural vegetation and fauna.

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drought

drought Late OE. drùað, f. *drūʒ-, base of drȳġe DRY; cf. (M)LG. drogede, (M)Du. droogte, f. droog dry; see -T 2.

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drought

droughtabout, bout, clout, devout, doubt, down-and-out, drought, flout, gout, grout, knout, Kraut, lout, mahout, misdoubt, nowt, out, out-and-out, owt, pout, Prout, right about, rout, scout, shout, snout, spout, sprout, stout, thereabout, thereout, throughout, timeout, tout, trout, way-out, without •layout, payout •buyout • blowout • layabout •gadabout • roundabout • knockabout •walkabout • runabout • turnabout •hereabout • roustabout •handout, standout •readout • hideout • dugout • blackout •checkout •breakout, stakeout, takeout •strikeout •knockout, lockout •walkout •cookout, lookout •workout • sell-out • fallout • pull-out •umlaut • litter lout • spin-out •burnout, turnout •hangout • wipeout •copout, dropout •waterspout • beansprout • clearout •sauerkraut • washout • printout •white-out • shoot-out •cut-out, shut-out

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