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151-669: The limited opportunities for self-reliance in the harsh desert environment have forced the refugees to rely on international humanitarian assistance for their survival. However, the Tindouf camps differ from the majority of refugee camps in the level of self-organization. Most affairs and camp life organization are run by the refugees themselves, with little outside interference. The camps are divided into five wilayat (districts) named after towns in Western Sahara; El Aaiun , Awserd , Smara , Dakhla and more recently Cape Bojador (or

302-537: A preferendum when the choices given allow the voters to weight their support for a policy. In Switzerland , for example, multiple choice referendums are common. Two multiple choice referendums were held in Sweden , in 1957 and in 1980, in which voters were offered three options. In 1977, a referendum held in Australia to determine a new national anthem was held, in which voters had four choices. In 1992, New Zealand held

453-530: A mammal adapted to desert life. It minimizes its water loss by producing concentrated urine and dry dung , and is able to lose 40% of its body weight through water loss without dying of dehydration. Carnivores can obtain much of their water needs from the body fluids of their prey. Many other hot desert animals are nocturnal , seeking out shade during the day or dwelling underground in burrows. At depths of more than 50 cm (20 in), these remain at between 30 and 32 °C (86 and 90 °F) regardless of

604-523: A modern state in 1848 . Italy ranks second with 78 national referendums : 72 popular referendums (51 of which were proposed by the Radical Party ), 4 constitutional referendums, one institutional referendum and one advisory referendum . A referendum usually offers the electorate a straight choice between accepting or rejecting a proposal. However some referendums give voters multiple choices, and some use transferable voting. This has also been called

755-455: A mosaic of smooth stones, often forming desert pavements , and little further erosion takes place. Other desert features include rock outcrops , exposed bedrock and clays once deposited by flowing water. Temporary lakes may form and salt pans may be left when waters evaporate. There may be underground sources of water, in the form of springs and seepages from aquifers . Where these are found, oases can occur. Plants and animals living in

906-456: A sand blasting mechanism which grinds away solid objects in its path as the kinetic energy of the wind is transferred to the ground. The sand eventually ends up deposited in level areas known as sand-fields or sand-seas, or piled up in dunes. Many people think of deserts as consisting of extensive areas of billowing sand dunes because that is the way they are often depicted on TV and in films, but deserts do not always look like this. Across

1057-428: A semi-arid climate and are less extreme than regular deserts. Like arid deserts, temperatures can vary greatly in semi deserts. They share some characteristics of a true desert and are usually located at the edge of deserts and continental dry areas. They usually receive precipitation from 250 to 500 mm (9.8 to 19.7 in) but this can vary due to evapotranspiration and soil nutrition. Semi-deserts can be found in

1208-432: A 'referendum' is often said to be a vote to change the federal constitution and 'plebiscite' a vote which does not affect the federal constitution. However, this is erroneous as not all federal referendums have been on constitutional matters (such as the 1916 Australian conscription referendum ), and state votes that likewise do not affect either the federal or state constitution are frequently said to be referendums (such as

1359-538: A central hospital and four regional hospitals. Men perform military service in the armed forces of the SADR. During the war years, at least some women were enrolled in auxiliary units guarding the refugee camps. The number of Sahrawi refugees in Tindouf camps is disputed and politically sensitive. Morocco argues that Polisario and Algeria overestimate the numbers to attract political attention and foreign aid, while Polisario accuses Morocco of attempting to restrict human aid as

1510-520: A country that houses about 26,000 Sahrawis refugees. UNHCR referred to Algeria's figure for many years, but in 2005 concern about it being inflated led the organization to reduce its working figure to 90,000 based on satellite imagery analysis. UNHCR is in dialogue with the Algerian Government and the Sahrawi refugee leadership, seeking to conduct a census to determine the exact number of refugees in

1661-438: A desert conglomerate . In time, bacteria that live on the surface of the stones accumulate a film of minerals and clay particles, forming a shiny brown coating known as desert varnish . Other non-sandy deserts consist of exposed outcrops of bedrock , dry soils or aridisols , and a variety of landforms affected by flowing water , such as alluvial fans , sinks or playas , temporary or permanent lakes , and oases. A hamada

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1812-505: A destructive effect on the exposed rocky surfaces. The repeated fluctuations put a strain on exposed rock and the flanks of mountains crack and shatter. Fragmented strata slide down into the valleys where they continue to break into pieces due to the relentless sun by day and chill by night. Successive strata are exposed to further weathering. The relief of the internal pressure that has built up in rocks that have been underground for aeons can cause them to shatter. Exfoliation also occurs when

1963-411: A five-option referendum on their electoral system. In 1982, Guam had a referendum that used six options, with an additional blank option for those wishing to (campaign and) vote for their own seventh option. A multiple choice referendum poses the question of how the result is to be determined. They may be set up so that if no single option receives the support of an absolute majority (more than half) of

2114-515: A form of basic democracy on the level of camp administration, and that this has improved the efficiency of aid distribution. Women are active on several levels of administration, and UNHCR has appraised their importance in camp administration and social structures. Algeria does not intervene in their organization. While the Algerian military has a significant presence in the nearby city of Tindouf, Algeria insists that responsibility for human rights in

2265-572: A generally similar meaning in modern usage and comes from the Latin plebiscita , which originally meant a decree of the Concilium Plebis (Plebeian Council), the popular assembly of the Roman Republic . Today, a referendum can also often be referred to as a plebiscite, but in some countries the two terms are used differently to refer to votes with differing types of legal consequences. In Australia,

2416-528: A large-scale opinion poll ). 'Referendum' is the gerundive form of the Latin verb referre , literally "to carry back" (from the verb ferre , "to bear, bring, carry" plus the inseparable prefix re- , here meaning "back" ). As a gerundive is an adjective , not a noun , it cannot be used alone in Latin, and must be contained within a context attached to a noun such as Propositum quod referendum est populo , "A proposal which must be carried back to

2567-415: A low basal metabolic rate and by remaining underground during the heat of the day, reducing loss of water through its skin and respiratory system when at rest. Herbivorous mammals obtain moisture from the plants they eat. Species such as the addax antelope , dik-dik , Grant's gazelle and oryx are so efficient at doing this that they apparently never need to drink. The camel is a superb example of

2718-483: A means of pressure on civilian refugee populations. The refugees' numbers will also be important in determining their political weight in the possible event of a referendum to determine Western Sahara's future status. Algerian authorities have estimated the number of Sahrawi refugees in Algeria to be 165,000. This has been supported by Polisario, although the movement recognizes that some refugees have rebased to Mauritania,

2869-409: A motivated minority of voters. Referendums may require a turnout threshold (also called a participation quorum) in order for the referendum to be considered legally valid. In a participation quorum a majority of those voting must approve of the referendum, and a certain percentage of population must have voted in order for the results to be approved. The usage of participation quorums in referendums

3020-484: A number of ways, generally combining total precipitation, number of days on which this falls, temperature, and humidity, and sometimes additional factors. For example, Phoenix, Arizona , receives less than 250 mm (9.8 in) of precipitation per year, and is immediately recognized as being located in a desert because of its aridity-adapted plants. The North Slope of Alaska's Brooks Range also receives less than 250 mm (9.8 in) of precipitation per year and

3171-525: A painful situation for the population in both Western Sahara and the refugee camps. In 2004, UNHCR managed a family visits exchange program for five-day visits for a limited number of people, going from the camps to the Moroccan-held territories and vice versa. The United Nations has also established telephone and mail services between the camps and Moroccan-held Western Sahara. While Polisario complains of repression of Sahrawi human rights activists in

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3322-409: A referendum are more likely to be driven by transient whims than by careful deliberation, or that they are not sufficiently informed to make decisions on complicated or technical issues. Also, voters might be swayed by propaganda , strong personalities, intimidation, and expensive advertising campaigns. James Madison argued that direct democracy is the " tyranny of the majority ". Some opposition to

3473-473: A referendum. Therefore avoid referendums. Therefore don't raise questions which require them, such as the big versus the little states. Some critics of the referendum attack the use of closed questions. A difficulty called the separability problem can plague a referendum on two or more issues. If one issue is in fact, or in perception, related to another on the ballot, the imposed simultaneous voting of first preference on each issue can result in an outcome which

3624-524: A separate vote on each of the multiple options as well as an additional decision about which of the multiple options should be preferred. In the Swedish case, in both referendums the 'winning' option was chosen by the Single Member Plurality ("first past the post") system. In other words, the winning option was deemed to be that supported by a plurality , rather than an absolute majority, of voters. In

3775-423: A series of long, linear dunes known as seif dunes may form. These also occur parallel to a strong wind that blows in one general direction. Transverse dunes run at a right angle to the prevailing wind direction. Star dunes are formed by variable winds, and have several ridges and slip faces radiating from a central point. They tend to grow vertically; they can reach a height of 500 m (1,600 ft), making them

3926-461: A sparse trophic network . Plant growth is limited by rainfall , temperature extremes and desiccating winds. Deserts have strong temporal variability in the availability of resources due to the total amount of annual rainfall and the size of individual rainfall events. Resources are often ephemeral or episodic, and this triggers sporadic animal movements and 'pulse and reserve' or 'boom-bust' ecosystem dynamics. Erosion and sedimentation are high due to

4077-439: A steady wind begins to blow, fine particles lying on the exposed ground begin to vibrate. At greater wind speeds, some particles are lifted into the air stream. When they land, they strike other particles which may be jerked into the air in their turn, starting a chain reaction . Once ejected, these particles move in one of three possible ways, depending on their size, shape and density; suspension , saltation or creep. Suspension

4228-571: A storm that may be many kilometers away. Most deserts are in basins with no drainage to the sea but some are crossed by exotic rivers sourced in mountain ranges or other high rainfall areas beyond their borders. The River Nile , the Colorado River and the Yellow River do this, losing much of their water through evaporation as they pass through the desert and raising groundwater levels nearby. There may also be underground sources of water in deserts in

4379-485: A tolerable level. In many ways, birds are the ablest to do this of the higher animals. They can move to areas of greater food availability as the desert blooms after local rainfall and can fly to faraway waterholes. In hot deserts, gliding birds can remove themselves from the over-heated desert floor by using thermals to soar in the cooler air at great heights. In order to conserve energy, other desert birds run rather than fly. The cream-colored courser flits gracefully across

4530-632: A type of cold desert . While they do not lack water, having a persistent cover of snow and ice, this is merely due to marginal evaporation rates and low precipitation. The McMurdo dry valleys of Antarctica, which lack water (whether rain, ice, or snow) much like a non-polar desert and even have such desert features as hypersaline lakes and intermittent streams that resemble (except for being frozen at their surfaces) hot or cold deserts for extreme aridity and lack of precipitation of any kind. Extreme winds and not seasonal heat desiccate these nearly-lifeless terrains. The concept of "biological desert" redefines

4681-400: A year; they have no annual seasonal cycle of precipitation and experience twelve-month periods with no rainfall at all. Arid deserts receive between 25 and 200 mm (1 and 8 in) in a year and semiarid deserts between 200 and 500 mm (8 and 20 in). However, such factors as the temperature, humidity, rate of evaporation and evapotranspiration, and the moisture storage capacity of

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4832-465: Is 150 km (93 mi) long and is the largest oasis in the Libyan Desert. A lake occupied this depression in ancient times and thick deposits of sandy-clay resulted. Wells are dug to extract water from the porous sandstone that lies underneath. Seepages may occur in the walls of canyons and pools may survive in deep shade near the dried up watercourse below. Lakes may form in basins where there

4983-508: Is a class of referendum required to be voted on if certain conditions are met or for certain government actions to be taken. They do not require any signatures from the public. In areas that use referendums a mandatory referendum is commonly used as a legally required step for ratification for constitutional changes, ratifying international treaties and joining international organizations, and certain types of public spending. Typical types of mandatory referendums include: An optional referendum

5134-408: Is a class of referendums that is put to the vote as a result of a demand. This may come from the executive branch, legislative branch, or a request from the people (often after meeting a signature requirement). Types of optional referendums include: From a political-philosophical perspective, referendums are an expression of direct democracy , but today, most referendums need to be understood within

5285-525: Is a jumble of eroded sandstone outcrops , canyons , blocks, pinnacles , fissures , slabs and ravines . In some places the wind has carved holes or arches, and in others, it has created mushroom-like pillars narrower at the base than the top. On the Colorado Plateau , it is water that has been the prevailing eroding force. Here, rivers, such as the Colorado , have cut their way over the millennia through

5436-482: Is a type of desert landscape consisting of a high rocky plateau where the sand has been removed by aeolian processes . Other landforms include plains largely covered by gravels and angular boulders, from which the finer particles have been stripped by the wind. These are called "reg" in the western Sahara, "serir" in the eastern Sahara, "gibber plains" in Australia and "saï" in central Asia. The Tassili Plateau in Algeria

5587-463: Is argued as the reason why, since World War II , there has been no provision in Germany for the holding of referendums at the federal level. In recent years, referendums have been used strategically by several European governments trying to pursue political and electoral goals. In 1995, John Bruton considered that All governments are unpopular. Given the chance, people would vote against them in

5738-551: Is brought in from the port of Oran to Rabouni by the World Food Programme (WFP) in collaboration with Algerian Red Crescent (ARC) and the Algerian government, while food distribution from Rabouni is organized by Polisario in collaboration with Western Sahara Red Crescent (WSRC). With the rise of a basic market economy, some refugees have been able to acquire television sets and use cars; several hundred satellite dishes have popped up in recent years. The refugee population

5889-623: Is continuous above 5,600 m (18,400 ft). Nevertheless, there is some plant life in the Atacama, in the form of specialist plants that obtain moisture from dew and the fogs that blow in from the Pacific. When rain falls in deserts, as it occasionally does, it is often with great violence. The desert surface is evidence of this with dry stream channels known as arroyos or wadis meandering across its surface. These can experience flash floods , becoming raging torrents with surprising rapidity after

6040-463: Is controversial, as higher requirements have been shown to reduced turnout and voter participation. With high participation quorums, the opposition of a referendum has an interest in abstaining from the vote instead of participating, in order to invalidate the referendum results through low turnout. This is a form of the no-show paradox . All others who are not voting for other reasons, including those with no opinion, are effectively also voting against

6191-648: Is displeasing to most. Several commentators have noted that the use of citizens' initiatives to amend constitutions has so tied the government to a jumble of popular demands as to render the government unworkable. A 2009 article in The Economist argued that this had restricted the ability of the California state government to tax the people and pass the budget, and called for an entirely new Californian constitution. A similar problem also arises when elected governments accumulate excessive debts. That can severely reduce

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6342-479: Is higher than that of forests or the sea. A desert is a region of land that is very dry because it receives low amounts of precipitation (usually in the form of rain, but it may be snow, mist or fog), often has little coverage by plants, and in which streams dry up unless they are supplied by water from outside the area. Deserts generally receive less than 250 mm (10 in) of precipitation each year. The potential evapotranspiration may be large but (in

6493-457: Is little or no vegetation, and firewood has to be gathered by car tens of kilometers away. Only a few of the camps have access to water, and the drinking sources are neither clean nor sufficient for the entire refugee population. Basic life cannot be sustained in this environment, and the camps are completely dependent on foreign aid. Food, drinking water, building materials and clothing are brought in by car by international aid agencies. Basic food

6644-551: Is often classified as a cold desert. Other regions of the world have cold deserts, including areas of the Himalayas and other high-altitude areas in other parts of the world. Polar deserts cover much of the ice-free areas of the Arctic and Antarctic. A non-technical definition is that deserts are those parts of Earth's surface that have insufficient vegetation cover to support a human population. Potential evapotranspiration supplements

6795-434: Is often less than 40 mm or 1.5 in) to being very far from the nearest available sources of moisture and are often in the lee of mountain ranges. Montane deserts are normally cold, or may be scorchingly hot by day and very cold by night as is true of the northeastern slopes of Mount Kilimanjaro . Polar deserts such as McMurdo Dry Valleys remain ice-free because of the dry katabatic winds that flow downhill from

6946-421: Is only possible for particles less than 0.1 mm (0.0039 in) in diameter. In a dust storm, these fine particles are lifted up and wafted aloft to heights of up to 6 km (3.7 mi). They reduce visibility and can remain in the atmosphere for days on end, conveyed by the trade winds for distances of up to 6,000 km (3,700 mi). Denser clouds of dust can be formed in stronger winds, moving across

7097-521: Is plagued by the lack of vegetables, nutritious food and medicines. According to the United Nations and the World Food Program , 40% of the children suffer from lack of iron, and 10% of the children below five years of age suffer from acute lack of nutrition. 32% are suffering from chronic lack of nutrition. 47% of the women suffer from lack of iron. Heavy flash rains and floods destroyed much of

7248-486: Is sufficient precipitation or meltwater from glaciers above. They are usually shallow and saline, and wind blowing over their surface can cause stress, moving the water over nearby low-lying areas. When the lakes dry up, they leave a crust or hardpan behind. This area of deposited clay, silt or sand is known as a playa . The deserts of North America have more than one hundred playas, many of them relics of Lake Bonneville which covered parts of Utah, Nevada and Idaho during

7399-657: Is the Atacama Desert . It is virtually devoid of life because it is blocked from receiving precipitation by the Andes mountains to the east and the Chilean Coast Range to the west. The cold Humboldt Current and the anticyclone of the Pacific are essential to keep the dry climate of the Atacama. The average precipitation in the Chilean region of Antofagasta is just 1 mm (0.039 in) per year. Some weather stations in

7550-450: Is the key to plant growth. It can only take place during the day as energy from the sun is required, but during the day, many deserts become very hot. Opening stomata to allow in the carbon dioxide necessary for the process causes evapotranspiration , and conservation of water is a top priority for desert vegetation. Some plants have resolved this problem by adopting crassulacean acid metabolism , allowing them to open their stomata during

7701-431: Is the specializations of mammalian kidneys shown by desert-inhabiting species. Many examples of convergent evolution have been identified in desert organisms, including between cacti and Euphorbia , kangaroo rats and jerboas , Phrynosoma and Moloch lizards. Deserts present a very challenging environment for animals. Not only do they require food and water but they also need to keep their body temperature at

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7852-528: Is very cold and carries little moisture so little precipitation occurs and what does fall, usually snow, is carried along in the often strong wind and may form blizzards, drifts and dunes similar to those caused by dust and sand in other desert regions. In Antarctica , for example, the annual precipitation is about 50 mm (2 in) on the central plateau and some ten times that amount on some major peninsulas. Based on precipitation alone, hyperarid deserts receive less than 25 mm (1 in) of rainfall

8003-770: The Oxford English Dictionary , which rules out such usage in both cases as follows: Referendums is logically preferable as a plural form meaning 'ballots on one issue' (as a Latin gerund, referendum has no plural). The Latin plural gerundive 'referenda', meaning 'things to be referred', necessarily connotes a plurality of issues. It is closely related to agenda , "those matters which must be driven forward", from ago , to impel or drive forwards; and memorandum , "that matter which must be remembered", from memoro , to call to mind, corrigenda , from rego , to rule, make straight, those things which must be made straight (corrected), etc. The term 'plebiscite' has

8154-416: The 2009 Western Australian daylight saving referendum ). Historically, they are used by Australians interchangeably and a plebiscite was considered another name for a referendum. In Ireland, 'plebiscite' referred to the vote to adopt its constitution, but a subsequent vote to amend the constitution is called a 'referendum', as is a poll of the electorate on a non-constitutional bill. The name and use of

8305-669: The Atacama Desert . Deserts of this type are often long and narrow and bounded to the east by mountain ranges. They occur in Namibia , Chile , southern California and Baja California . Other coastal deserts influenced by cold currents are found in Western Australia , the Arabian Peninsula and Horn of Africa , and the western fringes of the Sahara. In 1961, Peveril Meigs divided desert regions on Earth into three categories according to

8456-827: The Movement for Oneness and Jihad in West Africa (MOJWA) in Gao , Mali on the 18th of July 2012, being transferred to Burkina Faso and later to Spain. Poets Hadjatu Aliat Swelm and Hossein Moulud have written about life at the Gdeim Izik protest camp. Najla Mohamed-Lamin was recognised as one of the BBC's 100 women in 2023. Desert A desert is a landscape where little precipitation occurs and, consequently, living conditions create unique biomes and ecosystems. The lack of vegetation exposes

8607-561: The Rabuni , the administrative center of the refugee camps. The three hostages were two Spanish citizens (Enric Gonyalons and Ainhoa Fernández de Rincón) and an Italian woman (Rossella Urru); all members of humanitarian NGOs . During the abduction, Enric Gonyalons and a Sahrawi guard were wounded by the attackers, who according to POLISARIO sources came from Mali . At first, Brahim Gali , SADR ambassador in Algiers , said that Al-Qaeda Organization in

8758-462: The daira of Bojador). In addition, there is a smaller satellite camp known as "February 27", surrounding a boarding school for women, and an administrative camp called Rabouni . The encampments are spread out over a quite large area. While Laayoune, Smara, Awserd, February 27 and Rabouni all lie within an hour's drive of the Algerian city of Tindouf , the Dakhla camp lies 170 kilometres (110 mi) to

8909-616: The horse latitudes at 30° to 35° North and South. These belts are associated with the subtropical anticyclone and the large-scale descent of dry air. The Sahara Desert is of this type. Mid-latitude deserts occur between 30° and 50° North and South. They are mostly in areas remote from the sea where most of the moisture has already precipitated from the prevailing winds. They include the Tengger and Sonoran Deserts . Monsoon deserts are similar. They occur in regions where large temperature differences occur between sea and land. Moist warm air rises over

9060-414: The rocks , which consequently break in pieces. Although rain seldom occurs in deserts, there are occasional downpours that can result in flash floods. Rain falling on hot rocks can cause them to shatter, and the resulting fragments and rubble strewn over the desert floor are further eroded by the wind. This picks up particles of sand and dust, which can remain airborne for extended periods – sometimes causing

9211-417: The windward slope of the mountain range . When they descend on the leeward side, they warm and their capacity to hold moisture increases so an area with relatively little precipitation occurs. The Taklamakan Desert is an example, lying in the rain shadow of the Himalayas and receiving less than 38 mm (1.5 in) precipitation annually. Other areas are arid by virtue of being a very long way from

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9362-524: The 'referendum' is thought to have originated in the Swiss canton of Graubünden as early as the 16th century. After a reduction in the number of referendums in the Mid-twentieth century, the referendum as a political tool has been increasing in popularity since the 1970s. This increase has been attributed to dealignment of the public with political parties, as specific policy issues became more important to

9513-564: The 1977 Australian referendum, the winner was chosen by the system of preferential instant-runoff voting (IRV). Polls in Newfoundland (1949) and Guam (1982), for example, were counted under a form of the two-round system , and an unusual form of TRS was used in the 1992 New Zealand poll. Although California has not held multiple-choice referendums in the Swiss or Swedish sense (in which only one of several counter-propositions can be victorious, and

9664-486: The Atacama have never received rain. Evidence suggests that the Atacama may not have had any significant rainfall from 1570 to 1971. It is so arid that mountains that reach as high as 6,885 m (22,589 ft) are completely free of glaciers and, in the southern part from 25°S to 27°S, may have been glacier-free throughout the Quaternary , though permafrost extends down to an altitude of 4,400 m (14,400 ft) and

9815-600: The Islamic Maghreb (AQMI) was responsible for this incident. Mauritanian and Malian security sources also pointed to AQMI as perpetrators of the kidnapping. On 26 October, Algerian Army forces killed four AQMI members, suspects of the kidnappings. The kidnapping was widely condemned internationally, for example by the African Commission on Human and Peoples' Rights or the European Union . They were set free by

9966-596: The Moroccan-held parts of Western Sahara; the government of Morocco, dissident groups inside Polisario, as well as former members of Polisario , have claimed that the refugee camps occasionally are the scene of human rights abuse against the refugee population by the Polisario. The Polisario Front has acknowledged reports of mistreatment in the seventies and eighties, but deny the accusations of on-going abuse. Reports of beatings and torture, in many cases leading to death, of Moroccan prisoners of war who were formerly held in

10117-517: The absence of available water) the actual evapotranspiration may be close to zero. Semi-deserts are regions which receive between 250 and 500 mm (10 and 20 in) and when clad in grass, these are known as steppes . Most deserts on Earth such as the Sahara Desert , Grand Australian Desert and the Great Basin Desert , occur in low altitudes . One of the driest places on Earth

10268-539: The academic institutions of ‘27 February’ and ‘12 October’ as well as various technical training centres (without forgetting that Tindouf campements count 90.000 refugees) . While teaching materials are still scarce, the literacy rate has increased from about 5% at the formation of the camps to 90% in 1995. Children's education is obligatory, and several thousands have received university educations in Algeria , Cuba and Spain as part of aid packages. The camps have 27 clinics ,

10419-401: The air but soon fall back to earth, ejecting other particles in the process. Their weight prevents them from being airborne for long and most only travel a distance of a few meters (yards). The sand streams along above the surface of the ground like a fluid, often rising to heights of about 30 cm (12 in). In a really severe steady blow, 2 m (6 ft 7 in) is about as high as

10570-722: The amount of precipitation they received. In this now widely accepted system, extremely arid lands have at least twelve consecutive months without precipitation, arid lands have less than 250 mm (9.8 in) of annual precipitation, and semiarid lands have a mean annual precipitation of between 250 and 500 mm (9.8 and 19.7 in). Both extremely arid and arid lands are considered to be deserts while semiarid lands are generally referred to as steppes when they are grasslands. Deserts are also classified, according to their geographical location and dominant weather pattern, as trade wind, mid-latitude, rain shadow, coastal, monsoon, or polar deserts . Trade wind deserts occur either side of

10721-411: The barren rock is to be found in the so-called Dry Valleys of Antarctica that almost never get snow, which can have ice-encrusted saline lakes that suggest evaporation far greater than the rare snowfall due to the strong katabatic winds that even evaporate ice. Deserts, both hot and cold, play a part in moderating Earth's temperature, because they reflect more of the incoming light and their albedo

10872-521: The camps by Polisario against their will. However, the Central Intelligence Agency notes that there are about 100,000 refugees in Algerian sponsored camps near the town of Tindouf alone. The Tindouf area is located on the hammada , a vast desert plain of the Sahara Desert . Summer temperatures in this part of the hammada , historically known as "The Devil's Garden", are often above 50 °C and frequent sand storms disrupt normal life. There

11023-707: The camps continue to survive mainly on foreign and Algerian aid. Since the Polisario Front and Morocco are still at war, visits between the camps and the Moroccan-controlled parts of Western Sahara are virtually impossible, with the Moroccan Wall hindering movement through Western Sahara, and the Algeria–Morocco border closed added to the restriction on movement by the Polisario on the camps population. Thousands of families have been separated for up to 30 years,

11174-561: The camps during the 1990s, after Spain decided to pay pensions to Sahrawis who had been forcibly drafted as soldiers in the Tropas Nómadas during the colonial time. Money also came from Sahrawis working in Algeria or abroad, and from refugees who pursue a traditional bedouin and tuareg lifestyle, herding cattle in Algeria, Mauritania and the Polisario-held areas of Western Sahara. The private economy however remains very limited, and

11325-595: The camps in February 2006, prompting a crisis response from the UNHCR and the World Food Program (WFP), to replace destroyed housing with tents and provide food to cover for lost storages. The WFP has repeatedly expressed its concern over a shortage of donations, and warned of dire health consequences if needs are not met. The UNHCR warned in early 2007 that demands were not being met in the Sahrawi camps, and that malnutrition

11476-440: The camps lies with the Polisario. Camp residents are subject to the constitution and laws of SADR. A local justice system, with courts and prisons , is administered by Polisario. Local qadis ( sharia judges) have jurisdiction over personal status and family law issues. Polisario has prioritised education from the beginning, and the local authorities have established 29 preschools , 31 primary and seven secondary schools ,

11627-495: The camps were backed by some human rights organizations, which seems to have contributed to the release of the last of these prisoners by the summer of 2005. There are complaints of limitations on movement between the camps, with Morocco describing them as completely shut off from the outside world, but camp authorities maintain that this is untrue, and that they are simply engaged in registering movements for aid allocation purposes. Visiting human rights organizations have concluded that

11778-442: The camps' society, through emphasis on education, eradication of tribalism and emancipation of women. The role of Sahrawi women was central already in pre-colonial and colonial life, but was strengthened further during the war years (1975–1991), when Sahrawi women ran most of the camps' administration, while the men were fighting at the front. This, together with literacy and professional education classes, produced major advances in

11929-462: The camps, the Polisario has insisted on using mainly local staff for construction, teaching etc. It argues that this will help activate the refugee population, to avoid a sense of stagnation and hopelessness after 30 years in exile. However, jobs remain scarce and those Sahrawis educated at universities abroad can rarely if ever find opportunities to use their skills. Some Sahrawis work in nearby Tindouf city. A simple monetary economy began developing in

12080-457: The camps. In 1998, UN's Minurso mission identified 42,378 voting-age adults in the camps, counting only those who had contacted the mission's registration offices and subsequently been able to prove their descent from pre-1975 Western Sahara. No attempt was made to estimate the total population number in the camps. The Moroccan government contends that the total number of refugees is around 45,000 to 50,000, and also that these people are kept in

12231-457: The capture of large quantities of solar energy . English desert and its Romance cognates (including Italian and Portuguese deserto , French désert and Spanish desierto ) all come from the ecclesiastical Latin dēsertum (originally "an abandoned place"), a participle of dēserere , "to abandon". The correlation between aridity and sparse population is complex and dynamic, varying by culture, era, and technologies; thus

12382-516: The cellular structure of which has been modified to allow them to store water. When rain falls, the water is rapidly absorbed by the shallow roots and retained to allow them to survive until the next downpour, which may be months or years away. The giant saguaro cacti of the Sonoran Desert form "forests", providing shade for other plants and nesting places for desert birds. Saguaro grows slowly but may live for up to two hundred years. The surface of

12533-615: The coldest part of the year. Animals adapted to live in deserts are called xerocoles . There is no evidence that body temperature of mammals and birds is adaptive to the different climates, either of great heat or cold. In fact, with a very few exceptions, their basal metabolic rate is determined by body size, irrespective of the climate in which they live. Many desert animals (and plants) show especially clear evolutionary adaptations for water conservation or heat tolerance and so are often studied in comparative physiology , ecophysiology , and evolutionary physiology . One well-studied example

12684-597: The collision between airborne particles and by the impacts of saltating sand grains landing on the ground. The mechanism is little understood but the particles usually have a negative charge when their diameter is under 250 μm and a positive one when they are over 500 μm. Deserts and semi-deserts are home to ecosystems with low or very low biomass and primary productivity in arid or semi-arid climates. They are mostly found in subtropical high-pressure belts and major continental rain shadows . Primary productivity depends on low densities of small photoautotrophs that sustain

12835-586: The color of the underlying surface. The desert lark takes frequent dust baths which ensures that it matches its environment. Water and carbon dioxide are metabolic end products of oxidation of fats, proteins, and carbohydrates. Oxidising a gram of carbohydrate produces 0.60 grams of water; a gram of protein produces 0.41 grams of water; and a gram of fat produces 1.07 grams of water, making it possible for xerocoles to live with little or no access to drinking water. The kangaroo rat for example makes use of this water of metabolism and conserves water both by having

12986-468: The concept of desert, without the characteristic of aridity, not lacking water, but instead lacking life. Such places can be so-called "ocean deserts", which are mostly at the centers of gyres , but also hypoxic or anoxic waters such as dead zones . Deserts usually have a large diurnal and seasonal temperature range, with high daytime temperatures falling sharply at night. The diurnal range may be as much as 20 to 30 °C (36 to 54 °F) and

13137-443: The conditions are troublesome with regard to basic subsistence, but that the human rights situation is satisfactory. An OHCHR (United Nations' human rights monitors) visit to both Moroccan-controlled Western Sahara and the Tindouf refugee camps in 2006 documented no complaints of human rights abuse in the camps, but stressed the need for more information. However, the report, which severely criticized Moroccan conduct in Western Sahara,

13288-479: The context of representative democracy . They tend to be used quite selectively, covering issues such as changes in voting systems, where currently elected officials may not have the legitimacy or inclination to implement such changes. Since the end of the 18th century, hundreds of national referendums have been organised in the world; almost 600 national votes have been held in Switzerland since its inauguration as

13439-503: The desert floor to scarify the seed coat. The seed of the mesquite tree, which grows in deserts in the Americas, is hard and fails to sprout even when planted carefully. When it has passed through the gut of a pronghorn it germinates readily, and the little pile of moist dung provides an excellent start to life well away from the parent tree. The stems and leaves of some plants lower the surface velocity of sand-carrying winds and protect

13590-500: The desert need special adaptations to survive in the harsh environment. Plants tend to be tough and wiry with small or no leaves, water-resistant cuticles , and often spines to deter herbivory . Some annual plants germinate , bloom and die in the course of a few weeks after rainfall, while other long-lived plants survive for years and have deep root systems able to tap underground moisture. Animals need to keep cool and find enough food and water to survive. Many are nocturnal , and stay in

13741-587: The driest season, and others curl their leaves up to reduce transpiration. Others, such as aloes , store water in succulent leaves or stems or in fleshy tubers. Desert plants maximize water uptake by having shallow roots that spread widely, or by developing long taproots that reach down to deep rock strata for ground water. The saltbush in Australia has succulent leaves and secretes salt crystals, enabling it to live in saline areas. In common with cacti, many have developed spines to ward off browsing animals. Some desert plants produce seed which lies dormant in

13892-519: The effective margin for later governments. Both these problems can be moderated by a combination of other measures as Referendums occur occasionally rather than periodically as elections are and they don’t offer the same kind of formal opposition. Because referendums affect for a longer term than legislative deliberation, a turnout and supermajority requirement is necessary to maintain principles of majoritarianism. In republic polities, referendums could be used to bypass legislatures and representatives by

14043-455: The external temperature. Jerboas , desert rats , kangaroo rats and other small rodents emerge from their burrows at night and so do the foxes, coyotes, jackals and snakes that prey on them. Kangaroos keep cool by increasing their respiration rate, panting, sweating and moistening the skin of their forelegs with saliva . Mammals living in cold deserts have developed greater insulation through warmer body fur and insulating layers of fat beneath

14194-561: The form of springs , aquifers , underground rivers or lakes. Where these lie close to the surface, wells can be dug and oases may form where plant and animal life can flourish. The Nubian Sandstone Aquifer System under the Sahara Desert is the largest known accumulation of fossil water . The Great Man-Made River is a scheme launched by Libya's Muammar Gaddafi to tap this aquifer and supply water to coastal cities. Kharga Oasis in Egypt

14345-460: The form of the plural in English, which according to English grammar should be "referendums". The use of "referenda" as a plural form in English (treating it as a Latin word and attempting to apply to it the rules of Latin grammar) is unsupportable according to the rules of both Latin and English grammar. The use of "referenda" as a plural form is posited hypothetically as either a gerund or a gerundive by

14496-407: The formation of sand storms or dust storms . Wind-blown sand grains striking any solid object in their path can abrade the surface. Rocks are smoothed down, and the wind sorts sand into uniform deposits. The grains end up as level sheets of sand or are piled high in billowing sand dunes . Other deserts are flat, stony plains where all the fine material has been blown away and the surface consists of

14647-458: The fragmentation of harder granites , limestone and sandstone . There is a certain critical size (about 0.5 mm) below which further temperature-induced weathering of rocks does not occur and this provides a minimum size for sand grains. As the mountains are eroded, more and more sand is created. At high wind speeds, sand grains are picked up off the surface and blown along, a process known as saltation . The whirling airborne grains act as

14798-439: The ground from erosion. Even small fungi and microscopic plant organisms found on the soil surface (so-called cryptobiotic soil ) can be a vital link in preventing erosion and providing support for other living organisms. Cold deserts often have high concentrations of salt in the soil. Grasses and low shrubs are the dominant vegetation here and the ground may be covered with lichens . Most shrubs have spiny leaves and shed them in

14949-474: The ground have a marked effect on the degree of aridity and the plant and animal life that can be sustained. Rain falling in the cold season may be more effective at promoting plant growth, and defining the boundaries of deserts and the semiarid regions that surround them on the grounds of precipitation alone is problematic. A semi-arid desert or a steppe is a version of the arid desert with much more rainfall, vegetation and higher humidity. These regions feature

15100-432: The ground on its long legs, stopping periodically to snatch up insects. Like other desert birds, it is well-camouflaged by its coloring and can merge into the landscape when stationary. The sandgrouse is an expert at this and nests on the open desert floor dozens of kilometers (miles) away from the waterhole it needs to visit daily. Some small diurnal birds are found in very restricted localities where their plumage matches

15251-427: The ground rises quickly through a small pocket of cooler, low-pressure air above forming a whirling column of particles, a dust devil . Sandstorms occur with much less frequency than dust storms. They are often preceded by severe dust storms and occur when the wind velocity increases to a point where it can lift heavier particles. These grains of sand, up to about 0.5 mm (0.020 in) in diameter are jerked into

15402-429: The high desert floor, creating canyons that are over a mile (6,000 feet or 1,800 meters) deep in places, exposing strata that are over two billion years old. Sand and dust storms are natural events that occur in arid regions where the land is not protected by a covering of vegetation. Dust storms usually start in desert margins rather than the deserts themselves where the finer materials have already been blown away. As

15553-746: The high elevations of the Tabernas Desert (and some parts of the Spanish Plateu ), The Sahel , The Eurasian Steppe , most of Central Asia , the Western US , most of Northern Mexico , portions of South America (especially in Argentina ) and the Australian Outback . They usually feature BSh (hot steppe) or BSk (temperate steppe) in the Köppen climate classification . Coastal deserts are mostly found on

15704-450: The import of water from an outside source. Many trade routes have been forged across deserts, especially across the Sahara , and traditionally were used by caravans of camels carrying salt, gold, ivory and other goods. Large numbers of slaves were also taken northwards across the Sahara. Some mineral extraction also takes place in deserts, and the uninterrupted sunlight gives potential for

15855-523: The lack of heat to aid in the evaporation process. Deserts are sometimes classified as "hot" or "cold", "semiarid" or "coastal". The characteristics of hot deserts include high temperatures in summer; greater evaporation than precipitation, usually exacerbated by high temperatures, strong winds and lack of cloud cover; considerable variation in the occurrence of precipitation, its intensity and distribution; and low humidity. Winter temperatures vary considerably between different deserts and are often related to

16006-479: The land with a billowing leading edge. The sunlight can be obliterated and it may become as dark as night at ground level. In a study of a dust storm in China in 2001, it was estimated that 6.5 million tons of dust were involved, covering an area of 134,000,000 km (52,000,000 sq mi). The mean particle size was 1.44 μm. A much smaller scale, short-lived phenomenon can occur in calm conditions when hot air near

16157-469: The land, deposits its water content and circulates back to sea. Further inland, areas receive very little precipitation. The Thar Desert near the India/Pakistan border is of this type. In some parts of the world, deserts are created by a rain shadow effect. Orographic lift occurs as air masses rise to pass over high ground. In the process they cool and lose much of their moisture by precipitation on

16308-692: The last ice age when the climate was colder and wetter. These include the Great Salt Lake , Utah Lake , Sevier Lake and many dry lake beds. The smooth flat surfaces of playas have been used for attempted vehicle speed records at Black Rock Desert and Bonneville Speedway and the United States Air Force uses Rogers Dry Lake in the Mojave Desert as runways for aircraft and the Space Shuttle . Deserts have been defined and classified in

16459-510: The life processes of plants. Potential evapotranspiration , then, is the amount of water that could evaporate in any given region. As an example, Tucson, Arizona receives about 300 mm (12 in) of rain per year, however about 2,500 mm (98 in) of water could evaporate over the course of a year. In other words, about eight times more water could evaporate from the region than actually falls as rain. Rates of evapotranspiration in cold regions such as Alaska are much lower because of

16610-412: The location of the desert on the continental landmass and the latitude. Daily variations in temperature can be as great as 22 °C (40 °F) or more, with heat loss by radiation at night being increased by the clear skies. Cold deserts, sometimes known as temperate deserts, occur at higher latitudes than hot deserts, and the aridity is caused by the dryness of the air. Some cold deserts are far from

16761-682: The losing proposals are wholly null and void), it does have so many yes-or-no referendums at each election day that conflicts arise. The State's constitution provides a method for resolving conflicts when two or more inconsistent propositions are passed on the same day. This is a de facto form of approval voting —i.e. the proposition with the most "yes" votes prevails over the others to the extent of any conflict. Other voting systems that could be used in multiple-choice referendum are Condorcet method and quadratic voting (including quadratic funding ). Quorums are typically introduced to prevent referendum results from being skewed by low turnout or decided by

16912-404: The measurement of precipitation in providing a scientific measurement-based definition of a desert. The water budget of an area can be calculated using the formula P − PE ± S , wherein P is precipitation, PE is potential evapotranspiration rates and S is the amount of surface storage of water. Evapotranspiration is the combination of water loss through atmospheric evaporation and through

17063-597: The nearest available sources of moisture. Montane deserts are arid places with a very high altitude ; the most prominent example is found north of the Himalayas, in the Kunlun Mountains and the Tibetan Plateau . Many locations within this category have elevations exceeding 3,000 m (9,800 ft) and the thermal regime can be hemiboreal . These places owe their profound aridity (the average annual precipitation

17214-434: The neighbourhoods in political decision-making. Each of the four wilayas (districts) are divided into six or seven daïras (villages), which are in turn divided into hay s or barrios (neighborhoods). Local committees distribute basic goods, water and food, while "daïra" authorities made up by the representatives of the "hays" organize schools, cultural activities and medical services. Some argue that this results in

17365-409: The night to allow CO 2 to enter, and close them during the day, or by using C4 carbon fixation . Many desert plants have reduced the size of their leaves or abandoned them altogether. Cacti are present in both North and South America with a post-Gondwana origin. The genus is desert specialist, and in most species, the leaves have been dispensed with and the chlorophyll displaced into the trunks,

17516-514: The ocean and others are separated by mountain ranges from the sea, and in both cases, there is insufficient moisture in the air to cause much precipitation. The largest of these deserts are found in Central Asia. Others occur on the eastern side of the Rocky Mountains , the eastern side of the southern Andes and in southern Australia. Polar deserts are a particular class of cold desert. The air

17667-426: The outer surfaces of rocks split off in flat flakes. This is believed to be caused by the stresses put on the rock by repeated thermal expansions and contractions which induces fracturing parallel to the original surface. Chemical weathering processes probably play a more important role in deserts than was previously thought. The necessary moisture may be present in the form of dew or mist. Ground water may be drawn to

17818-466: The pavement is formed. It may be that after the sand and dust is blown away by the wind the stones jiggle themselves into place; alternatively, stones previously below ground may in some way work themselves to the surface. Very little further erosion takes place after the formation of a pavement, and the ground becomes stable. Evaporation brings moisture to the surface by capillary action and calcium salts may be precipitated, binding particles together to form

17969-433: The people". The addition of the verb sum (3rd person singular, est ) to a gerundive, denotes the idea of necessity or compulsion, that which "must" be done, rather than that which is "fit for" doing. Its use as a noun in English is not considered a strictly grammatical usage of a foreign word but is rather a newly coined English noun, which follows English grammatical usage, not Latin grammatical usage. This determines

18120-458: The public than party identifiers. The term "referendum" covers a variety of different meanings, and the terminology is different depending on the us that holds them. A referendum can be binding or advisory. In some countries, different names are used for these two types of referendum. Referendums can be further classified by who initiates them. David Altman proposes four dimensions that referendums can be classified by: A mandatory referendum

18271-522: The referendum has arisen from its use by dictators such as Adolf Hitler and Benito Mussolini who, it is argued, used the plebiscite to disguise oppressive policies as populism . Dictators may also make use of referendums as well as show elections to further legitimize their authority such as António de Oliveira Salazar in 1933 ; Benito Mussolini in 1934 ; Adolf Hitler in 1934 , 1936 ; Francisco Franco in 1947 ; Park Chung Hee in 1972 ; and Ferdinand Marcos in 1973 . Hitler's use of plebiscites

18422-853: The referendum to take place. In one such challenge, in 2017, the Spanish Constitutional Court suspended the Catalonia 's independence referendum . In post-referendum disputes, they challenge the result. British courts dismissed post-referendum challenges of the Brexit referendum. International tribunals have traditionally not interfered with referendum disputes. In 2021, the European Court of Human Rights extended its jurisdiction to referendums in its judgment Toplak and Mrak v. Slovenia , initiated by two disabled voters over polling place access . In Political Governance states that voters in

18573-499: The referendum. In the 2005 Italian fertility laws referendum , opposition to the proposed loosening of laws on research on embryos and on allowing in-vitro fertilization , campaigned for people to abstain from voting to drive down turnout. Although a majority of people voted yes for the changes in the law, the results were invalid because participation was low. Important referendums are frequently challenged in courts. In pre-referendum disputes, plaintiffs have often tried to prevent

18724-438: The rock surface experiences even greater temperature differentials. During the day the sky is usually clear and most of the sun 's radiation reaches the ground, but as soon as the sun sets, the desert cools quickly by radiating heat into space. In hot deserts, the temperature during daytime can exceed 45 °C (113 °F) in summer and plunge below freezing point at night during winter. Such large temperature variations have

18875-603: The role of women in Sahrawi society. The return of large numbers of Sahrawi men since the cease fire in 1991 may have slowed this development according to some observers, but women still run a majority of the camps' administration, and the Sahrawi women's union UNMS is very active in promoting their role. Two women who had been residents of the camps however claimed that women in the refugee camps are deprived of their fundamental rights and are victims of exclusion and sexual aggression. While there are several international organizations ( ECHO , WFP , Oxfam , UNHCR , etc.) working in

19026-503: The sand stream can rise as the largest sand grains do not become airborne at all. They are transported by creep, being rolled along the desert floor or performing short jumps. During a sandstorm, the wind-blown sand particles become electrically charged . Such electric fields , which range in size up to 80 kV/m, can produce sparks and cause interference with telecommunications equipment. They are also unpleasant for humans and can cause headaches and nausea. The electric fields are caused by

19177-435: The shade or underground during the heat of the day. They tend to be efficient at conserving water, extracting most of their needs from their food and concentrating their urine . Some animals remain in a state of dormancy for long periods, ready to become active again during the rare rainfall. They then reproduce rapidly while conditions are favorable before returning to dormancy. People have struggled to live in deserts and

19328-441: The sheet consists of thin horizontal layers of coarse silt and very fine to medium grain sand, separated by layers of coarse sand and pea-gravel which are a single grain thick. These larger particles anchor the other particles in place and may also be packed together on the surface so as to form a miniature desert pavement. Small ripples form on the sand sheet when the wind exceeds 24 km/h (15 mph). They form perpendicular to

19479-434: The skin and various thermoregulatory strategies to maintain its body temperature in one of the harshest environments on Earth. Referendum A referendum , plebiscite , or ballot measure is a direct vote by the electorate (rather than their representatives ) on a proposal, law, or political issue. A referendum may be either binding (resulting in the adoption of a new policy ) or advisory (functioning like

19630-412: The skin. The arctic weasel has a metabolic rate that is two or three times as high as would be expected for an animal of its size. Birds have avoided the problem of losing heat through their feet by not attempting to maintain them at the same temperature as the rest of their bodies, a form of adaptive insulation. The emperor penguin has dense plumage, a downy under layer, an air insulation layer next to

19781-466: The soil until sparked into growth by rainfall. With annuals , such plants grow with great rapidity and may flower and set seed within weeks, aiming to complete their development before the last vestige of water dries up. For perennial plants, reproduction is more likely to be successful if the seed germinates in a shaded position, but not so close to the parent plant as to be in competition with it. Some seed will not germinate until it has been blown about on

19932-630: The southeast. The camps are also the headquarters of the 6th military region of the Saharawi Arab Democratic Republic . The refugee camps are governed by Polisario , being administratively part of the Sahrawi Arab Democratic Republic (SADR). SADR's government in exile and administration are located in the Rabouni camp. The Tindouf camps are divided into administrative sub-units electing their own officials to represent

20083-464: The sparse vegetation cover and the activities of large mammals and people. Plants and animals in deserts are mostly adapted to extreme and prolonged water deficits , but their reproductive phenology often responds to short episodes of surplus. Competitive interactions are weak. Plants face severe challenges in arid environments. Problems they need to solve include how to obtain enough water, how to avoid being eaten and how to reproduce. Photosynthesis

20234-440: The surface by evaporation and the formation of salt crystals may dislodge rock particles as sand or disintegrate rocks by exfoliation. Shallow caves are sometimes formed at the base of cliffs by this means. As the desert mountains decay, large areas of shattered rock and rubble occur. The process continues and the end products are either dust or sand. Dust is formed from solidified clay or volcanic deposits whereas sand results from

20385-464: The surface of the ground. Dunes are sometimes solitary, but they are more often grouped together in dune fields. When these are extensive, they are known as sand seas or ergs . The shape of the dune depends on the characteristics of the prevailing wind. Barchan dunes are produced by strong winds blowing across a level surface and are crescent-shaped with the concave side away from the wind. When there are two directions from which winds regularly blow,

20536-561: The surrounding mountains. Former desert areas presently in non-arid environments, such as the Sandhills in Nebraska , are known as paleodeserts. In the Köppen climate classification system, deserts are classed as BWh (hot desert) or BWk (temperate desert). In the Thornthwaite climate classification system , deserts would be classified as arid megathermal climates. Polar deserts are

20687-597: The surrounding semi-arid lands for millennia. Nomads have moved their flocks and herds to wherever grazing is available, and oases have provided opportunities for a more settled way of life. The cultivation of semi-arid regions encourages erosion of soil and is one of the causes of increased desertification. Desert farming is possible with the aid of irrigation , and the Imperial Valley in California provides an example of how previously barren land can be made productive by

20838-399: The tallest type of dune. Rounded mounds of sand without a slip face are the rare dome dunes, found on the upwind edges of sand seas. In deserts where large amounts of limestone mountains surround a closed basin , such as at White Sands National Park in south-central New Mexico , occasional storm runoff transports dissolved limestone and gypsum into a low-lying pan within the basin where

20989-407: The trunk is folded like a concertina , allowing it to expand, and a large specimen can hold eight tons of water after a good downpour. Other xerophytic plants have developed similar strategies by a process known as convergent evolution . They limit water loss by reducing the size and number of stomata, by having waxy coatings and hairy or tiny leaves. Some are deciduous, shedding their leaves in

21140-614: The unprotected surface of the ground to denudation . About one-third of the land surface of the Earth 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. Deserts are formed by weathering processes as large variations in temperature between day and night put strains on

21291-496: The use of the word desert can cause confusion. In English before the 20th century, desert was often used in the sense of "unpopulated area", without specific reference to aridity ; but today the word is most often used in its climate-science sense (an area of low precipitation). Phrases such as " desert island " and " Great American Desert ", or Shakespeare 's "deserts of Bohemia " ( The Winter's Tale ) in previous centuries did not necessarily imply sand or aridity; their focus

21442-657: The votes, resort can be made to the two-round system or instant-runoff voting , which is also called IRV and PV. In 2018 the Irish Citizens' Assembly considered the conduct of future referendums in Ireland , with 76 of the members in favour of allowing more than two options, and 52% favouring preferential voting in such cases. Other people regard a non-majoritarian methodology like the Modified Borda Count (MBC) as more inclusive and more accurate. Swiss referendums offer

21593-416: The water evaporates, depositing the gypsum and forming crystals known as selenite . The crystals left behind by this process are eroded by the wind and deposited as vast white dune fields that resemble snow-covered landscapes. These types of dune are rare, and only form in closed arid basins that retain the highly soluble gypsum that would otherwise be washed into the sea. A large part of the surface area of

21744-476: The western edges of continental land masses in regions where cold currents approach the land or cold water upwellings rise from the ocean depths. The cool winds crossing this water pick up little moisture and the coastal regions have low temperatures and very low rainfall, the main precipitation being in the form of fog and dew. The range of temperatures on a daily and annual scale is relatively low, being 11 °C (20 °F) and 5 °C (9 °F) respectively in

21895-404: The wind blows, saltation and creep take place on the windward side of the dune and individual grains of sand move uphill. When they reach the crest, they cascade down the far side. The upwind slope typically has a gradient of 10° to 20° while the lee slope is around 32°, the angle at which loose dry sand will slip. As this wind-induced movement of sand grains takes place, the dune moves slowly across

22046-511: The wind direction and gradually move across the surface as the wind continues to blow. The distance between their crests corresponds to the average length of jumps made by particles during saltation. The ripples are ephemeral and a change in wind direction causes them to reorganise. Sand dunes are accumulations of windblown sand piled up in mounds or ridges. They form downwind of copious sources of dry, loose sand and occur when topographic and climatic conditions cause airborne particles to settle. As

22197-450: The world's deserts consists of flat, stone-covered plains dominated by wind erosion. In " eolian deflation ", the wind continually removes fine-grained material, which becomes wind-blown sand. This exposes coarser-grained material, mainly pebbles with some larger stones or cobbles , leaving a desert pavement , an area of land overlaid by closely packed smooth stones forming a tessellated mosaic. Different theories exist as to how exactly

22348-470: The world, around 20% of desert is sand, varying from only 2% in North America to 30% in Australia and over 45% in Central Asia. Where sand does occur, it is usually in large quantities in the form of sand sheets or extensive areas of dunes . A sand sheet is a near-level, firm expanse of partially consolidated particles in a layer that varies from a few centimeters to a few meters thick. The structure of

22499-440: Was severe. Refugees International has noted that the situation is especially precarious in Dakhla, the most inaccessible of the camps. In October 2015, heavy rainfalls flooded the refugee camps again, destroying houses (made of sand-bricks), tents and food provisions. More than 11,000 families were affected. The European Commission refers to the Sahrawi refugees as the "forgotten refugees". Polisario has attempted to modernize

22650-570: Was slammed as biased and partisan by the Moroccan government. In April 2010, the Sahrawi government had called the UN to supervise human rights in the liberated territories and refugee camps, stating that "We are ready to fully cooperate with UN human rights observers in the territory under our control. The United Nations should take this proposal seriously, and ask Morocco to do likewise". On 23 October 2011, three European humanitarian aid workers were kidnapped in

22801-459: Was the sparse population. Deserts occupy about one third of Earth's land surface. Bottomlands may be salt -covered flats. Eolian processes are major factors in shaping desert landscapes. Polar deserts (also seen as "cold deserts") have similar features, except the main form of precipitation is snow rather than rain. Antarctica is the world's largest cold desert (composed of about 98% thick continental ice sheet and 2% barren rock). Some of

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