Drought

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Contraction/Desiccation cracks in dry earth (Sonoran desert, Mexico). Drought.jpg
Contraction/Desiccation cracks in dry earth (Sonoran desert, Mexico).

A drought or drouth is a natural disaster of below-average precipitation in a given region, resulting in prolonged shortages in the water supply, whether atmospheric, surface water or ground water. A drought can last for months or years, or may be declared after as few as 15 days. [1] It can have a substantial impact on the ecosystem and agriculture of the affected region [2] and harm to the local economy. [3] 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.

Surface water water on a planets surface, rather than underground or evaporated

Surface water is water on the surface of the planet such as in a river, lake, wetland, or ocean. It can be contrasted with groundwater and atmospheric water.

Ecosystem A community of living organisms together with the nonliving components of their environment

An ecosystem is a community of living organisms in conjunction with the nonliving components of their environment, interacting as a system. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the system through photosynthesis and is incorporated into plant tissue. By feeding on plants and on one-another, animals play an important role in the movement of matter and energy through the system. They also influence the quantity of plant and microbial biomass present. By breaking down dead organic matter, decomposers release carbon back to the atmosphere and facilitate nutrient cycling by converting nutrients stored in dead biomass back to a form that can be readily used by plants and other microbes.

Agriculture Cultivation of plants and animals to provide useful products

Agriculture is the science and art of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people to live in cities. The history of agriculture began thousands of years ago. After gathering wild grains beginning at least 105,000 years ago, nascent farmers began to plant them around 11,500 years ago. Pigs, sheep and cattle were domesticated over 10,000 years ago. Plants were independently cultivated in at least 11 regions of the world. Industrial agriculture based on large-scale monoculture in the twentieth century came to dominate agricultural output, though about 2 billion people still depended on subsistence agriculture into the twenty-first.

Contents

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. [4] 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). [5]

Cactus family of mostly succulent plants, adapted to dry environments

A cactus is a member of the plant family Cactaceae, a family comprising about 127 genera with some 1750 known species of the order Caryophyllales. The word "cactus" derives, through Latin, from the Ancient Greek κάκτος, kaktos, a name originally used by Theophrastus for a spiny plant whose identity is not certain. Cacti occur in a wide range of shapes and sizes. Most cacti live in habitats subject to at least some drought. Many live in extremely dry environments, even being found in the Atacama Desert, one of the driest places on earth. Cacti show many adaptations to conserve water. Almost all cacti are succulents, meaning they have thickened, fleshy parts adapted to store water. Unlike many other succulents, the stem is the only part of most cacti where this vital process takes place. Most species of cacti have lost true leaves, retaining only spines, which are highly modified leaves. As well as defending against herbivores, spines help prevent water loss by reducing air flow close to the cactus and providing some shade. In the absence of leaves, enlarged stems carry out photosynthesis. Cacti are native to the Americas, ranging from Patagonia in the south to parts of western Canada in the north—except for Rhipsalis baccifera, which also grows in Africa and Sri Lanka.

Mass migration

Mass migration refers to the migration of large groups of people from one geographical area to another. Mass migration is distinguished from individual or small scale migration; and also from seasonal migration, which may occur on a regular basis.

Recorded history historical narrative based on a written record or other documented communication

Recorded history or written history is a historical narrative based on a written record or other documented communication. It contrasts with other narratives of the past, such as mythological, oral or archeological traditions. For broader world history, recorded history begins with the accounts of the ancient world around the 4th millennium BC, and coincides with the invention of writing. For some geographic regions or cultures, written history is limited to a relatively recent period in human history because of the limited use of written records. Moreover, human cultures do not always record all of the information relevant to later historians, such as the full impact of natural disasters or the names of individuals; thus, recorded history for particular types of information is limited based on the types of records kept. Because of this, recorded history in different contexts may refer to different periods of time depending on the topic.

Causes of drought

Precipitation deficiency

Mechanisms of producing precipitation include convective, stratiform, [6] and orographic rainfall. [7] Convective processes involve strong vertical motions that can cause the overturning of the atmosphere in that location within an hour and cause heavy precipitation, [8] while stratiform processes involve weaker upward motions and less intense precipitation over a longer duration. [9] 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 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. Once a region is within drought, feedback mechanisms such as local arid air, [10] hot conditions which can promote warm core ridging, [11] and minimal evapotranspiration can worsen drought conditions.

Stratus cloud genus of clouds, low-level clouds characterized by horizontal layering with a uniform base, as opposed to convective or cumuliform clouds that are formed by rising thermals

Stratus clouds are low-level clouds characterized by horizontal layering with a uniform base, as opposed to convective or cumuliform clouds that are formed by rising thermals. More specifically, the term stratus is used to describe flat, hazy, featureless clouds of low altitude varying in color from dark gray to nearly white. The word "stratus" comes from the Latin prefix "strato-", meaning "layer". Stratus clouds may produce a light drizzle or a small amount of snow. These clouds are essentially above-ground fog formed either through the lifting of morning fog or through cold air moving at low altitudes over a region. Some call these clouds "high fog" for the fog-like cloud. While light rain may fall, this cloud does not indicate much meteorological activity.

Orographic lift

Orographic lift occurs when an air mass is forced from a low elevation to a higher elevation as it moves over rising terrain. As the air mass gains altitude it quickly cools down adiabatically, which can raise the relative humidity to 100% and create clouds and, under the right conditions, precipitation.

Pressure system relative peak or lull in the sea level pressure distribution

A pressure system is a relative peak or lull in the sea level pressure distribution. The surface pressure at sea level varies minimally, with the lowest value measured 87 kilopascals (26 inHg) and the highest recorded 108.57 kilopascals (32.06 inHg). High- and low-pressure systems evolve due to interactions of temperature differentials in the atmosphere, temperature differences between the atmosphere and water within oceans and lakes, the influence of upper-level disturbances, as well as the amount of solar heating or radiationized cooling an area receives. Pressure systems cause weather to be experienced locally. Low-pressure systems are associated with clouds and precipitation that minimize temperature changes throughout the day, whereas high-pressure systems normally associate with dry weather and mostly clear skies with larger diurnal temperature changes due to greater radiation at night and greater sunshine during the day. Pressure systems are analyzed by those in the field of meteorology within surface weather maps.

Dry season

Within the tropics, distinct, wet and dry seasons emerge due to the movement of the Intertropical Convergence Zone or Monsoon trough. [12] The dry season greatly increases drought occurrence, [13] 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, elephants, [14] and wildebeest. Because of the lack of water in the plants, bushfires are common. [15] 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). [16] Periods of warmth quicken the pace of fruit and vegetable production, [17] increase evaporation and transpiration from plants, [18] and worsen drought conditions. [19]

Wet season yearly period of high rainfall, especially in the tropics

The monsoon season is the time of year when most of a region's average annual rainfall occurs. Generally the season lasts at least a month. The term "green season" is also sometimes used as a euphemism by tourist authorities. Areas with wet seasons are dispersed across portions of the tropics and subtropics.

A season is a division of the year marked by changes in weather, ecology, and amount of daylight. On Earth, seasons result from Earth's orbit around the Sun and Earth's axial tilt relative to the ecliptic plane. In temperate and polar regions, the seasons are marked by changes in the intensity of sunlight that reaches the Earth's surface, variations of which may cause animals to undergo hibernation or to migrate, and plants to be dormant. Various cultures define the number and nature of seasons based on regional variations.

Intertropical Convergence Zone

The Intertropical Convergence Zone (ITCZ), known by sailors as the doldrums or the calms, is the area encircling Earth near the Equator, where the northeast and southeast trade winds converge.

El Niño

Regional impacts of warm ENSO episodes (El Nino) El Nino regional impacts.png
Regional impacts of warm ENSO episodes (El Niño)

Drier and hotter weather occurs in parts of the Amazon River Basin, Colombia, and 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, Zimbabwe, Mozambique, and Botswana. 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. Drier-than-normal conditions are also in general observed in Queensland, inland Victoria, inland New South Wales, and eastern Tasmania from June to August. As warm water spreads from the west Pacific and the 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. [20]

Amazon River longest river in South America

The Amazon River in South America is the largest river by discharge volume of water in the world, and by some definitions it is the longest.

Colombia Country in South America

Colombia, officially the Republic of Colombia, is a sovereign state largely situated in the northwest of South America, with territories in Central America. Colombia shares a border to the northwest with Panama, to the east with Venezuela and Brazil and to the south with Ecuador and Peru. It shares its maritime limits with Costa Rica, Nicaragua, Honduras, Jamaica, Haiti, and the Dominican Republic. Colombia is a unitary, constitutional republic comprising thirty-two departments, with the capital in Bogota.

Central America central geographic region of the Americas

Central America is located on the southern tip of North America, or is sometimes defined as a subcontinent of the Americas, bordered by Mexico to the north, Colombia to the southeast, the Caribbean Sea to the east, and the Pacific Ocean to the west and south. Central America consists of seven countries: Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua, and Panama. The combined population of Central America has been estimated to be 41,739,000 and 42,688,190.

Erosion and human activities

Human activity can directly trigger exacerbating factors such as over farming, excessive irrigation, [21] deforestation, and erosion adversely impact the ability of the land to capture and hold water. [22] In arid climates, the main source of erosion is wind. [23] 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. [24]

Irrigation artificial application of water to the land or soil

sultan anas maked dams for free

Deforestation removal of forest and conversion of the land to non-forest use

Deforestation, clearance, clearcutting or clearing is the removal of a forest or stand of trees from land which is then converted to a non-forest use. Deforestation can involve conversion of forest land to farms, ranches, or urban use. The most concentrated deforestation occurs in tropical rainforests. About 31% of Earth's land surface is covered by forests.

Erosion Processes which remove soil and rock from one place on the Earths crust, then transport it to another location where it is deposited

In earth science, erosion is the action of surface processes that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location. This natural process is caused by the dynamic activity of erosive agents, that is, water, ice (glaciers), snow, air (wind), plants, animals, and humans. In accordance with these agents, erosion is sometimes divided into water erosion, glacial erosion, snow erosion, wind (aeolic) erosion, zoogenic erosion, and anthropogenic erosion. The particulate breakdown of rock or soil into clastic sediment is referred to as physical or mechanical erosion; this contrasts with chemical erosion, where soil or rock material is removed from an area by its dissolving into a solvent, followed by the flow away of that solution. Eroded sediment or solutes may be transported just a few millimetres, or for thousands of kilometres.

Fields outside Benambra, Victoria, Australia suffering from drought conditions. Fields outside benambra.jpg
Fields outside Benambra, Victoria, Australia suffering from drought conditions.

Loess is a homogeneous, typically nonstratified, porous, friable, slightly coherent, often calcareous, fine-grained, silty, pale yellow or buff, windblown (Aeolian) sediment. [25] 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. [26] Loess tends to develop into highly rich soils. Under appropriate climatic conditions, areas with loess are among the most agriculturally productive in the world. [27] 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. [23] Wind erosion is much more severe in arid areas and during times of drought. 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. [28]

Climatic changes

Activities resulting in global climate change are expected to trigger droughts with a substantial impact on agriculture [29] [30] throughout the world, and especially in developing nations. [31] [32] [33] Overall, global warming will result in increased world rainfall. [34] 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. [35]

Types of drought

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: [36]

  1. Meteorological drought occurs when there is a prolonged time with less than average precipitation. [37] Meteorological drought usually precedes the other kinds of drought. [38]
  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 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. [39]
  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, 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. [40] Similar circumstances also place their largest lake, Balkhash, at risk of completely drying out. [41]

Consequences of drought

A Mongolian gazelle dead due to drought. Mongolian Gazelle dead of drought.jpg
A Mongolian gazelle dead due to drought.

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

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, [43] [44] because lower water-flows reduce dilution of pollutants and increase contamination of remaining water-sources. Common consequences of drought include:

Globally

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. [55] Hunter-gatherer migrations in 9,500 BC Chile have been linked to the phenomenon, [56] as has the exodus of early humans out of Africa and into the rest of the world around 135,000 years ago. [57]

A South Dakota farm during the Dust Bowl, 1936 Dust Bowl - Dallas, South Dakota 1936.jpg
A South Dakota farm during the Dust Bowl, 1936

Examples

Well-known historical droughts include:

Affected areas in the western Sahel belt during the 2012 drought. Sahel Map-Africa rough.png
Affected areas in the western Sahel belt during the 2012 drought.

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. [61]

Approximately 2.4 billion people live in the drainage basin of the Himalayan rivers. [62] 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 million people. [63] [64] [65] 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. [66] [67]

Drought affected area in Karnataka, India in 2012. Drought affected area in Karnataka, India, 2012.jpg
Drought affected area in Karnataka, India in 2012.

In 2005, parts of the Amazon basin experienced the worst drought in 100 years. [68] [69] 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. [70] [71] 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. [72]

Lake Chad in a 2001 satellite image. The lake has shrunk by 95% since the 1960s. ShrinkingLakeChad-1973-1997-EO.jpg
Lake Chad in a 2001 satellite image. The lake has shrunk by 95% since the 1960s.

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. [75] 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. [76] Australia could experience more severe droughts and they could become more frequent in the future, a government-commissioned report said on July 6, 2008. [77] 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. [78] 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 1984–85, 2006 and 2011. [79] During the 2011 drought, an estimated 50,000 to 150,000 people were reported to have died, [80] though these figures and the extent of the crisis are disputed. [81] In February 2012, the UN announced that the crisis was over due to a scaling up of relief efforts and a bumper harvest. [82] Aid agencies subsequently shifted their emphasis to recovery efforts, including digging irrigation canals and distributing plant seeds. [82]

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. [83]

Protection, mitigation and relief

Succulent plants are well-adapted to survive long periods of drought. Huntington Desert Garden Cactus (etc).jpg
Succulent plants are well-adapted to survive long periods of drought.
Water distribution on Marshall Islands during El Nino. FEMA - 917 - Photograph by Angel Santiago taken on 04-03-1998 in Marshall Islands.jpg
Water distribution on Marshall Islands during El Niño.

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 ever-increasing population densities. President Roosevelt on April 27, 1935, signed documents creating the 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). [84]

Aerosols over the Amazon each September for four burning seasons (2005 through 2008) during the Amazon basin drought. The aerosol scale (yellow to dark reddish-brown) indicates the relative amount of particles that absorb sunlight. September Smoke Over the Amazon from 2005-2008.png
Aerosols over the Amazon each September for four burning seasons (2005 through 2008) during the Amazon basin drought. The aerosol scale (yellow to dark reddish-brown) indicates the relative amount of particles that absorb sunlight.

Strategies for drought protection, mitigation or relief include:

See also

Regional:

Related Research Articles

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Desertification

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Geography of Mauritania

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Soil erosion washing or blowing away of the top layer of soil

Soil erosion is the displacement of the upper layer of soil, one form of soil degradation. This natural process is caused by the dynamic activity of erosive agents, that is, water, ice (glaciers), snow, air (wind), plants, animals, and humans. In accordance with these agents, erosion is sometimes divided into water erosion, glacial erosion, snow erosion, wind (aeolean) erosion, zoogenic erosion, and anthropogenic erosion. Soil erosion may be a slow process that continues relatively unnoticed, or it may occur at an alarming rate causing a serious loss of topsoil. The loss of soil from farmland may be reflected in reduced crop production potential, lower surface water quality and damaged drainage networks.

Sahel transition zone in Africa

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Precipitation product of the condensation of atmospheric water vapour that falls under gravity

In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation include drizzle, rain, sleet, snow, graupel and hail. Precipitation occurs when a portion of the atmosphere becomes saturated with water vapor, so that the water condenses and "precipitates". Thus, fog and mist are not precipitation but suspensions, because the water vapor does not condense sufficiently to precipitate. Two processes, possibly acting together, can lead to air becoming saturated: cooling the air or adding water vapor to the air. Precipitation forms as smaller droplets coalesce via collision with other rain drops or ice crystals within a cloud. Short, intense periods of rain in scattered locations are called "showers."

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Land degradation

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Sahel drought

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Natural disasters in India

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Historic desertification is the study of the desert-forming process from a historic perspective. It was presumed in the past that the main causes of desertification lay in overuse of the land resulting in impoverishment of the soil, reduced vegetation cover, increased risk of drought and the resulting wind erosion. However recent projects to regreen deserts have not met with the success envisaged, and cast doubts on this theory. Research suggests that it is extreme events rather than drought caused by low annual precipitation, that do the most damage. Heavy downpours resulting in flash floods wash away sediment and there seems to have been an increased number of extreme events in the Levant at the end of the Byzantine period. The decline of settlements in the desert belt at this time may have been caused by these extreme events rather than a reduction in annual precipitation.

Tropical savanna climate

Tropical savanna climate or tropical wet and dry climate is a type of climate that corresponds to the Köppen climate classification categories "Aw" and "As". Tropical savanna climates have monthly mean temperatures above 18 °C (64 °F) in every month of the year and typically a pronounced dry season, with the driest month having less than 60 mm of precipitation and also less than 100 – [total annual precipitation {mm}/25] of precipitation.

Water scarcity Lack of fresh water resources to meet water demand

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Climate of Argentina

The climate of Argentina is a vastly complex subject, as the vast size of the country and wide variation in altitude make for a wide range of climate types. Summers are the warmest and wettest season in most of the country except in most of Patagonia where it is the driest season. Winters are normally mild in the north, cool in the center and cold in the southern parts experiencing frequent frost and snow. Because southern parts of the country are moderated by the surrounding oceans, the cold is less intense and prolonged than areas at similar latitudes in the northern hemisphere. Spring and autumn are transition seasons that generally feature mild weather.

Desert Area of land where little precipitation occurs

A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to the processes of denudation. About one-third of the land surface of the world is arid or semi-arid. This includes much of the polar regions where little precipitation occurs and which are sometimes called polar deserts or "cold deserts". Deserts can be classified by the amount of precipitation that falls, by the temperature that prevails, by the causes of desertification or by their geographical location.

Rain liquid water in the form of droplets that have condensed from atmospheric water vapor and then precipitated

Rain is liquid water in the form of droplets that have condensed from atmospheric water vapor and then become heavy enough to fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides suitable conditions for many types of ecosystems, as well as water for hydroelectric power plants and crop irrigation.

Droughts are a relatively common feature of the weather in the United Kingdom, with one around every 5–10 years on average. These droughts are usually during the summer, when a blocking high causes hot, dry weather for an extended period. However droughts can vary in their characteristics. All types of drought cause issues across all sectors, with impacts extending to the ecosystem, agriculture and the economy of the whole country in severe cases of drought. The south east of the country usually suffers most, as it has the highest population and the lowest average precipitation per year, which is even lower in a drought. Even in these areas in severe droughts, the definition, impacts, effects and management are all minimal in comparison to drought prone areas such as Australia and parts of the United States. In recent years however, the summers of 2007, 2008, 2009, August 2010 and 2012 were wetter than normal, 2007 being wettest on record.

The effects of climate change in Saskatchewan are now being observed in parts of the province. There is evidence of reduction of biomass in Saskatchewan's boreal forests that is linked by researchers to drought-related water stress stemming from global warming, most likely caused by greenhouse gas emissions. While studies, as early as 1988 have shown that climate change will affect agriculture, whether the effects can be mitigated through adaptations of cultivars, or crops, is less clear. Resiliency of ecosystems may decline with large changes in temperature. The provincial government has responded to the threat of climate change by introducing a plan to reduce carbon emissions, "The Saskatchewan Energy and Climate Change Plan", in June 2007.

There are many pressing environmental issues in Mongolia that are detrimental to both human and biophysical wellness. These problems have arisen in part due to natural factors, but increasingly because of human actions. One of these issues is climate change, which will be responsible for an increase in desertification, natural disasters, and land degradation. Another is deforestation, which is expanding due to human recklessness, pests, disease, and fire. Mongolian lands are becoming more arid through desertification, a process that is being exacerbated due to irresponsible land use. Additionally, more and more species are disappearing and at risk for extinction. And, especially in population centers, Mongolians deal with air and water pollution caused by industrialization.

References

  1. It's a scorcher - and Ireland is officially 'in drought' Irish Independent, 2013-07-18.
  2. Living With Drought Archived 2007-02-18 at the Wayback Machine
  3. Australian Drought and Climate Change, retrieved on June 7th 2007.
  4. Keddy, P.A. (2007), Plants and Vegetation: Origins, Processes, Consequences, Cambridge, UK.: Cambridge University Press, ISBN   978-0521864800
  5. "Driest Place: Atacama Desert, Chile". Extreme Science. Retrieved September 25, 2016..
  6. Emmanouil N. Anagnostou (2004). "A convective/stratiform precipitation classification algorithm for volume scanning weather radar observations". Meteorological Applications . 11 (4): 291–300. Bibcode:2004MeApp..11..291A. doi:10.1017/S1350482704001409.
  7. A.J. Dore; M. Mousavi-Baygi; R.I. Smith; J. Hall; D. Fowler; T.W. Choularton (June 2006). "A model of annual orographic precipitation and acid deposition and its application to Snowdonia". Atmospheric Environment. 40 (18): 3316–3326. Bibcode:2006AtmEn..40.3316D. doi:10.1016/j.atmosenv.2006.01.043.
  8. Robert Penrose Pearce (2002). Meteorology at the Millennium. Academic Press. p. 66. ISBN   978-0-12-548035-2 . Retrieved 2009-01-02.
  9. Houze, Robert A., Jr. (1993). Cloud dynamics. San Diego: Academic Press. ISBN   9780080502106. OCLC   427392836.
  10. Roland Paepe; Rhodes Whitmore Fairbridge; Saskia Jelgersma (1990). Greenhouse Effect, Sea Level and Drought. Springer Science & Business Media. p. 22. ISBN   978-0792310174.
  11. Joseph S. D'Aleo; Pamela G. Grube (2002). The Oryx Resource Guide to El Niño and La Niña. Greenwood Publishing Group. pp. 48–49. ISBN   978-1573563789.
  12. Bin Wang (2006-01-13). The Asian Monsoon. Springer Science & Business Media. p. 206. ISBN   978-3540406105.
  13. Vijendra K. Boken; Arthur P. Cracknell; Ronald L. Heathcote (2005-03-24). Monitoring and Predicting Agricultural Drought : A Global Study: A Global Study. Oxford University Press. p. 349. ISBN   978-0198036784.
  14. TONY RENNELL (June 29, 2007). "It's dry season and elephants are desperately seeking water - but poachers lie in wait". London: Daily Mail.
  15. "Wet & Dry Seasons". Archived from the original on 2012-03-21. Retrieved 2018-12-23.
  16. Alistair B. Fraser (1994-11-27). "Bad Meteorology: The reason clouds form when air cools is because cold air cannot hold as much water vapor as warm air" . Retrieved 2015-02-17.
  17. Cooperative Extension Service (January 2014). Home Vegetable Gardening in Kentucky (PDF). University of Kentucky. p. 19. Retrieved 2015-02-18.
  18. North Carolina State University (2013-08-09). "Evapotranspiration". Archived from the original on 2015-02-19. Retrieved 2015-02-18.
  19. National Oceanic and Atmospheric Administration (2002-05-16). "Warm Temperatures and Severe Drought Continued in April Throughout Parts of the United States; Global Temperature For April Second Warmest on Record" . Retrieved 2015-02-18.
  20. "channelnewsasia.com - February 2010 is driest month for S'pore since records began in 1869". 3 March 2010. Archived from the original on 3 March 2010. Retrieved 5 November 2017.CS1 maint: BOT: original-url status unknown (link)
  21. "A biblical tragedy as Sea of Galilee faces drought". BelfastTelegraph.co.uk.
  22. "Kenya: Deforestation exacerbates droughts, floods". forests.org. Archived from the original on 2011-09-27. Retrieved 2008-05-24.
  23. 1 2 Vern Hofman; Dave Franzen (1997). "Emergency Tillage to Control Wind Erosion". North Dakota State University Extension Service. Retrieved 2009-03-21.
  24. United States Geological Survey (2004). "Dunes – Getting Started" . Retrieved 2009-03-21.
  25. F. von Richthofen (1882). "On the mode of origin of the loess". Geological Magazine (Decade II). 9 (7): 293–305. Bibcode:1882GeoM....9..293R. doi:10.1017/S001675680017164X.
  26. K.E.K. Neuendorf; J.P. Mehl, Jr.; J.A. Jackson (2005). Glossary of Geology. Springer-Verlag, New York. p. 779. ISBN   978-3-540-27951-8.
  27. Arthur Getis; Judith Getis and Jerome D. Fellmann (2000). Introduction to Geography, Seventh Edition. McGraw-Hill. p. 99. ISBN   978-0-697-38506-2.
  28. Wiggs, Giles F.S. (2011). "Geomorphological hazards in drylands". In Thomas, David S.G. Arid Zone Geomorphology: Process, Form and Change in Drylands. John Wiley & Sons. p. 588. ISBN   978-0-470-71076-0. The distribution of all the water on the earth’s surface is not even. Some places have lots of fresh water (rivers, lakes, lagoons, ponds etc.) and are continuously replenished by rainfall, runoffs and water from underground. Others places too are known to have very little water. Therefore, if a region that has lots of rainfall, goes for a couple of weeks without rains, and people, animals and plants begin to experience a bit of dryness, it can be called drought. At the same time, that condition may be very normal for places with no water, and can go for months without any rains with little problems.
  29. NOAA Drought and climate change: implications for the West Archived 2008-06-25 at the Wayback Machine December 2002
  30. Smith, Adam B.; Katz, Richard W. (2013). "Smith A.B. and R. Katz, 2013: U.S. Billion-dollar weather and climate disasters: Data sources, trends, accuracy and biases. Natural Hazards, 67, 387–410, doi:10.1007/s11069-013-0566-5" (PDF). Natural Hazards. 67 (2): 387–410. doi:10.1007/s11069-013-0566-5 . Retrieved 5 November 2017.
  31. "Finfacts: Irish business, finance news on economics". finfacts.com.
  32. Fuel costs, drought influence price increase Archived September 13, 2012, at Archive.today
  33. "Nigerian Scholar Links Drought, Climate Change to Conflict in Africa - US Department of State". state.gov. Archived from the original on 28 October 2005.
  34. "Is Water the New Oil?". Common Dreams.
  35. Sunshade' for global warming could cause drought 2 August 2007 New Scientist, Catherine Brahic
  36. "Qianfeng Wang". ResearchGate.
  37. Swain, S; et al. (2017). "Application of SPI, EDI and PNPI using MSWEP precipitation data over Marathwada, India". IEEE International Geoscience and Remote Sensing Symposium (IGARSS. 2017: 5505–5507. doi:10.1109/IGARSS.2017.8128250. ISBN   978-1-5090-4951-6 . Retrieved 15 June 2018.
  38. "What is a Drought?" (PDF). National Oceanic and Atmospheric Administration. August 2006. Retrieved 2007-04-10.
  39. The alleviating trend of drought in the Huang-Huai-Hai Plain of China based on the daily SPEI. International Journal of Climatology.2015. doi: 10.1002/joc.4244 Wang, Qianfeng, Shi, Peijun, Lei, Tianjie, Geng, Guangpo, Liu, Jinghui, Mo, Xinyu, Li, Xiaohan, Zhou, Hongkui. and Wu, Jianjun
  40. "BBC NEWS - Asia-Pacific - Dam project aims to save Aral Sea". bbc.co.uk.
  41. "BBC NEWS - Asia-Pacific - Kazakh lake 'could dry up'". bbc.co.uk.
  42. Prokurat, Sergiusz (2015). "Drought and water shortages in Asia as a threat and economic problem" (PDF). Journal of Modern Science. 26 (3). Retrieved 4 August 2016.
  43. Mosley LM (2014). Drought impacts on the water quality of freshwater systems; review and integration. Earth Science Reviews. DOI: 10.1016/j.earscirev.2014.11.010.
  44. 10. Mosley LM, Zammit B, Leyden E, Heneker TM, Hipsey MR, Skinner D, and Aldridge KT (2012). The Impact of Extreme Low Flows on the Water Quality of the Lower Murray River and Lakes (South Australia). Water Resources Management 26: 3923–3946.
  45. C.Michael Hogan. 2010. Abiotic factor. Ed. Emily Monosson. Encyclopedia of Earth. National Council for Science and the Environment, Washington DC Archived June 8, 2013, at the Wayback Machine
  46. Drought affecting US hydroelectric production | Daily Estimate Archived October 2, 2011, at the Wayback Machine
  47. "Parched village sues to shut tap at Coke / Drought-hit Indians say plant draining groundwater". SFGate.
  48. "Sweden closes nuclear plants over safety fears". Greenpeace International. Archived from the original on 2009-01-10. Retrieved 2016-02-06.
  49. "BBC NEWS - Asia-Pacific - Australians face snake invasion". bbc.co.uk.
  50. 1 2 "TFS Article". tamu.edu. Archived from the original on 11 July 2003.
  51. Mosley LM, Zammit B, Jolley A, and Barnett L (2014). Acidification of lake water due to drought. Journal of Hydrology. 511: 484–493.
  52. 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.
  53. 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.
  54. "Toxins from freshwater algae found in San Francisco Bay shellfish" . Retrieved 5 November 2017.
  55. "BBC - Weather Centre - Features - History and Religion - Weather in the Bible - Drought and Famine" . Retrieved 5 November 2017.
  56. "Ancient Chile Migration Mystery Tied to Drought". nationalgeographic.com.
  57. Drought pushed ancient African immigration [ permanent dead link ]
  58. Oliver Wetter et al: The year-long unprecedented European heat and drought of 1540 – a worst case. In: Climatic Change , June 2014, doi:10.1007/s10584-014-1184-2
  59. Andreas Frey (2018-08-04). "Elf Monate ohne Regen: Die Angst vor der Megadürre des Jahres 1540 geht um" (in German). Neue Zürcher Zeitung . Retrieved 2018-08-06.
  60. "Climate change tripled likelihood of drought that pushed Cape Town water crisis to 'Day Zero' brink, say scientists". Red Cross Red Crescent Climate Centre. Reliefweb. 16 July 2018. Retrieved 22 November 2018.
  61. Thomson Reuters Foundation. "Thomson Reuters Foundation". alertnet.org.
  62. "People & the Planet > climate change > newsfile > big melt threatens millions, says un". peopleandplanet.net. Archived from the original on 19 August 2007.
  63. "Ganges, Indus may not survive: climatologists". rediff.com.
  64. "People's Daily Online - Glaciers melting at alarming speed". peopledaily.com.cn.
  65. "BBC NEWS - Science/Nature - Himalaya glaciers melt unnoticed". bbc.co.uk.
  66. "Glaciers Are Melting Faster Than Expected, UN Reports". ScienceDaily.
  67. Water shortage worst in decades, official says, Los Angeles Times
  68. staff. "Amazon Drought Worst in 100 Years". www.ens-newswire.com. Retrieved 5 November 2017.
  69. Drought Threatens Amazon Basin - Extreme conditions felt for second year running Archived May 27, 2013, at the Wayback Machine
  70. Amazon rainforest 'could become a desert' , The Independent, July 23, 2006. Retrieved September 28, 2006.
  71. Dying Forest: One year to save the Amazon, The Independent, July 23, 2006. Retrieved September 28, 2006.
  72. Climate change a threat to Amazon rainforest, warns WWF, World Wide Fund for Nature, March 9, 2996. Retrieved September 28, 2006.
  73. "Plan B Updates - 47: Disappearing Lakes, Shrinking Seas - EPI". earth-policy.org.
  74. "Shrinking African Lake Offers Lesson on Finite Resources". nationalgeographic.com.
  75. Sensitivity of the Australian Monsoon to insolation and vegetation: Implications for human impact on continental moisture balance, Geological Society of America
  76. Australian rivers 'face disaster', BBC News
  77. Australia faces worse, more frequent droughts: study, Reuters
  78. Metropolis strives to meet its thirst, BBC News
  79. Sara Pantuliano and Sara Pavanello (2004) Taking drought into account Addressing chronic vulnerability among pastoralists in the Horn of Africa Archived March 7, 2012, at the Wayback Machine Overseas Development Institute
  80. "Fatal Failure: Did Aid Agencies Let Up To 100,000 Somalis Die in 2011?". Time. January 18, 2012.
  81. Warah, Rasna (2 October 2011). "Manufacturing a famine: How Somalia crisis became a fund-raising opportunity". The East African. Retrieved 16 March 2013.
  82. 1 2 Gettleman, Jeffrey (3 February 2012). "U.N. Says Somalia Famine Has Ended, but Crisis Isn't Over" . Retrieved 5 November 2017 via www.nytimes.com.
  83. "Methodists make appeal for famine threatened West Africa - Ekklesia". ekklesia.co.uk.
  84. "State Conservation District Laws Development and Variations – NRCS". usda.gov.
  85. Matt Weiser; Jeremy B. White (2014-06-01). "Should California build dams, reservoirs to help with future droughts?". Fresno Bee. Archived from the original on 2015-03-20. Retrieved 2015-02-18.
  86. "Cloud seeding helps alleviate drought". chinadaily.com.cn.
  87. NRC. "Critical Issues in Weather Modification Research".
  88. City of Santa Barbara (2014-12-22). "Desalinization" . Retrieved 2015-02-18.
  89. BBC's From Our Own Correspondent on khat water usage

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