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In ecology, an oasis (; ) is a fertile area of a
desert 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 denudation. About on ...
or semi-desert environmentBattesti, Vincent (2005) Jardins au désert: Évolution des pratiques et savoirs oasiens: Jérid tunisien. Paris: IRD éditions.
.
that sustains plant life and provides habitat for animals. Surface water may be present, or water may only be accessible from wells or underground channels created by humans. In geography, an oasis may be a current or past rest stop on a transportation route, or less-than-verdant location that nonetheless provides access to underground water through deep wells created and maintained by humans. The word ''oasis'' came into English from la, oasis, from grc, ὄασις, , which in turn is a direct borrowing from Demotic Egyptian. The word for ''oasis'' in the latter-attested
Coptic language Coptic (Bohairic Coptic: , ) is a language family of closely related dialects, representing the most recent developments of the Egyptian language, and historically spoken by the Copts, starting from the third-century AD in Roman Egypt. Coptic ...
(the descendant of Demotic Egyptian) is ''wahe'' or ''ouahe'' which means a "dwelling place". Oasis in Arabic is ''al-wāḥat'' ( واحه ).


Description

Oases develop in “
hydrologically Hydrology () is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and environmental watershed sustainability. A practitioner of hydrology is call ...
favored” locations that have attributes such as a high water table, seasonal lakes, or blockaded wadis. Oases are made when sources of freshwater, such as underground rivers or aquifers, irrigate the surface naturally or via man-made wells. The presence of water on the surface or underground is necessary and the local or regional management of this essential resource is strategic, but not sufficient to create such areas: continuous human work and know-how (a technical and social culture) are essential to maintain such ecosystems.Vincent Battesti, The Power of a Disappearance: Water in the Jerid region of Tunisia ''in'' B. R. Johnston ''et al.'' (eds), ''Water, Cultural Diversity & Global Environmental Change: Emerging Trends, Sustainable Futures?'', 2012, UNESCO/Springer,
.
Stereotypically, an oasis has a “central pool of open water surrounded by a ring of water-dependent shrubs and trees…which are in turn encircled by an outlying transition zone to desert plants.” Rain showers provide subterranean water to sustain natural oases, such as the Tuat. Substrata of impermeable rock and stone can trap water and retain it in pockets, or on long faulting subsurface ridges or volcanic dikes water can collect and percolate to the surface. Any incidence of water is then used by
migrating bird Bird migration is the regular seasonal movement, often north and south along a flyway, between breeding and wintering grounds. Many species of bird migrate. Migration carries high costs in predation and mortality, including from hunting by ...
s, which also pass seeds with their droppings which will grow at the water's edge forming an oasis. It can also be used to plant crops. Oases in the Middle East and North Africa cover about , however, they support the livelihood of about 10 million inhabitants. The stark ratio of oasis to desert land in the world means that the oasis ecosystem is “relatively minute, rare and precious.” There are 90 “major oases” within the Sahara Desert. Some of their fertility may derive from irrigation systems called '' foggaras'', ''khettaras,'' ''lkhttarts'', or a variety of other regional names''.'' In some oases systems, there is “a geometrical system of raised channels that release controlled amounts of the water into individual plots, soaking the soil.” Oases often have human histories that are measured in millennia. Archeological digs at Ein Gedi in the Dead Sea Valley have found evidence of settlement dating to 6,000 BC. Al-Ahsa on the Arabian Peninsula shows evidence of human residence dating to the Neolithic. Anthropologically, the oasis is “an area of sedentary life, which associates the city 'medina''or village 'ksar''">ksar.html" ;"title="'ksar">'ksar''with its surrounding feeding source, the palm grove, within a relational and circulatory nomadic system.” The location of oases has been of critical importance for trade and transportation routes in desert areas; caravans must travel via oases so that supplies of water and food can be replenished. Thus, political or military control of an oasis has in many cases meant control of trade on a particular route. For example, the oases of Awjila, Ghadames and Kufra, situated in modern-day Libya, have at various times been vital to both north–south and east–west Trans-Saharan trade, trade in the Sahara Desert. The location of oases also informed the Darb El Arba'īn trade route from Sudan to Egypt, as well as the caravan route from the Niger River to Tangier, Morocco. The
Silk Road The Silk Road () was a network of Eurasian trade routes active from the second century BCE until the mid-15th century. Spanning over 6,400 kilometers (4,000 miles), it played a central role in facilitating economic, cultural, political, and reli ...
“traced its course from water hole to water hole, relying on oasis communities such as Turpan in China and
Samarkand fa, سمرقند , native_name_lang = , settlement_type = City , image_skyline = , image_caption = Clockwise from the top:Registan square, Shah-i-Zinda necropolis, Bibi-Khanym Mosque, view inside Shah-i-Zinda, ...
in Uzbekistan.” According to the United Nations, “Oases are at the very heart of the overall development of peri-Saharan countries due to their geographical location and the fact they are preferred migration routes in times of famine or insecurity in the region.” Oases in Oman, on the
Arabian Peninsula The Arabian Peninsula, (; ar, شِبْهُ الْجَزِيرَةِ الْعَرَبِيَّة, , "Arabian Peninsula" or , , "Island of the Arabs") or Arabia, is a peninsula of Western Asia, situated northeast of Africa on the Arabian Plate ...
near the Persian Gulf, vary somewhat from the Saharan form. While still located in an arid or semi-arid zone with a date palm overstory, these oases are usually located ''below plateaus'' and “watered either by springs or by ''aflaj'', tunnel systems dug into the ground or carved into the rock to tap underground aquifers.” This rainwater harvesting system “never developed a serious salinity problem.” In the drylands of southwestern North America, there is a habitat form called Palm Oasis (alternately Palm Series or Oasis Scrub Woodland) that has the native California fan palm as the overstory species. These Palm Oases can be found in California, Arizona, Baja California, and
Sonora Sonora (), officially Estado Libre y Soberano de Sonora ( en, Free and Sovereign State of Sonora), is one of the 31 states which, along with Mexico City, comprise the Administrative divisions of Mexico, Federal Entities of Mexico. The state is d ...
.


Agroforestry

People who live in an oasis must manage land and water use carefully. The most important plant in an oasis is the date palm ( ''Phoenix dactylifera'' L.), which forms the upper layer. These palm trees provide shade for smaller understory trees like
apricot An apricot (, ) is a fruit, or the tree that bears the fruit, of several species in the genus ''Prunus''. Usually, an apricot is from the species '' P. armeniaca'', but the fruits of the other species in ''Prunus'' sect. ''Armeniaca'' are also ...
s,
dates Date or dates may refer to: *Date (fruit), the fruit of the date palm (''Phoenix dactylifera'') Social activity *Dating, a form of courtship involving social activity, with the aim of assessing a potential partner **Group dating *Play date, an ...
, figs ,
olive The olive, botanical name ''Olea europaea'', meaning 'European olive' in Latin, is a species of small tree or shrub in the family Oleaceae, found traditionally in the Mediterranean Basin. When in shrub form, it is known as ''Olea europaea'' ...
s, and peach trees, which form the middle layer. Market-garden vegetables, some cereals (such as
sorghum ''Sorghum'' () is a genus of about 25 species of flowering plants in the grass family (Poaceae). Some of these species are grown as cereals for human consumption and some in pastures for animals. One species is grown for grain, while many othe ...
, barley,
millet Millets () are a highly varied group of small-seeded grasses, widely grown around the world as cereal crops or grains for fodder and human food. Most species generally referred to as millets belong to the tribe Paniceae, but some millets al ...
, and wheat), and/or mixed animal
fodder Fodder (), also called provender (), is any agriculture, agricultural foodstuff used specifically to feed domesticated livestock, such as cattle, domestic rabbit, rabbits, sheep, horses, chickens and pigs. "Fodder" refers particularly to food g ...
, are grown in the bottom layer where there is more moisture. The oasis is integrated into its desert environment through an often close association with nomadic transhumant livestock farming (very often pastoral and sedentary populations are clearly distinguished). The fertility of the oasis soil is restored by “cyclic organic inputs of animal origin.” In summary, an oasis palm grove is a highly anthropized and irrigated area that supports a traditionally intensive and polyculture-based agriculture. Responding to environmental constraints, the three strata create what is called the "
oasis effect The oasis effect refers to the creation of a local microclimate that is cooler than the surrounding Arid, dry area due to evaporation or evapotranspiration of a water source or plant life and higher albedo of plant life than bare ground. The oasis ...
." The three layers and all their interaction points create a variety of combinations of “horizontal wind speed, relative air temperature and relative air humidity.” The plantings—through a
virtuous cycle A vicious circle (or cycle) is a complex chain of events that reinforces itself through a feedback loop, with detrimental results. It is a system with no tendency toward equilibrium (social, economic, ecological, etc.), at least in the short r ...
of wind reduction, increased shade and evapotranspiration—create a microclimate favorable to crops; “measurements taken in different oases have showed that the potential evapotranspiration of the areas was reduced by 30 to 50 percent within the oasis.” The keystone date palm trees are “a main income source and staple food for local populations in many countries in which they are cultivated, and have played significant roles in the economy, society, and environment of those countries.” Challenges for date palm oasis polycultures include “low rainfall, high temperatures, water resources often high in salt content, and high incidence of pests.”


Distressed systems

Many historic oases have struggled with drought and inadequate maintenance. According to a United Nations report on the future of oases in the Sahara and
Sahel The Sahel (; ar, ساحل ' , "coast, shore") is a region in North Africa. It is defined as the ecoclimatic and biogeographic realm of transition between the Sahara to the north and the Sudanian savanna to the south. Having a hot semi-arid c ...
, “Increasingly…oases are subject to various pressures, heavily influenced by the effects of climate change, decreasing groundwater levels and a gradual loss of cultural heritage due to a fading historical memory concerning traditional water management techniques. These natural pressures are compounded by demographic pressures and the introduction of modern water pumping techniques that can disrupt traditional resource management schemes, particularly in the North Saharan oases.” For example, five historic oases in the Western Desert of Egypt (
Kharga The Kharga Oasis (Arabic: , ) ; Coptic: ( "Oasis of Hib", "Oasis of Psoi") is the southernmost of Egypt's five western oases. It is located in the Western Desert, about 200 km (125 miles) to the west of the Nile valley. "Kharga" or ...
, Dakhla, Farafra, Baharyia, and Siwa) once had “flowing spring and wells” but due to the decline of groundwater heads because of overuse for land reclamation projects those water sources are no more and the oases suffer as a result. Morocco has lost two-thirds of its oasis habitat over the last 100 years due to heat, drought, and water scarcity. The Ferkla Oases in Morocco once drew on water from the Ferkla, Sat and Tangarfa Rivers but they are now dry but for a few days a year.


List of places called oases


Old World oases

* Kharga Oasis, Egypt * Al-Qatif and Al Ahsa - Saudi Arabia * Al-Ula Oasis, Saudi Arabia * Al Ain - UAE * Buraimi Oasis, Maghta, and
Bahla Bahla ( ar, بهلا) is a town, located 40 km away from Nizwa, and about 200 km from Oman's capital Muscat which lies in the Ad Dakhiliyah Governorate of Oman. It is notable as the home of one of the oldest fortresses in the country, t ...
- Oman * Bahariya Oasis, Farafra, and
Siwa Oasis The Siwa Oasis ( ar, واحة سيوة, ''Wāḥat Sīwah,'' ) is an urban oasis in Egypt; between the Qattara Depression and the Great Sand Sea in the Western Desert (Egypt), Western Desert, 50 km (30 mi) east of the Libyan Egypt–Li ...
- Egypt * Ghadames and Kufra - Libya *
Jalo Oasis Jalo Oasis (or Jalu, or Gialo) is an oasis in Cyrenaica, Libya, located west of the Great Sand Sea and about 250 km south-east of the Gulf of Sidra. Quite large, long and up to wide, it supports a number of settlements, the largest of whic ...
- Libya * Ouargla, Taut, and
Timimoun Timimoun ( ar, ﺗﻴﻤﻴﻤﻮن) is a town and commune, and capital of Timimoun District, in Adrar Province, south-central Algeria. According to the 2008 census it has a population of 33,060, up from 28,595 in 1998, with an annual growth rate ...
- Algeria * Tozeur and Tamerza - Tunisia * Ourzazat - Morocco *
Kebili Oasis Kebili ( ') is a town in the south of Tunisia and one of the main cities in the Nefzaoua region. It is located south of Tunisia. It is the capital of the Kebili Governorate. History Kebili is one of the oldest oases in Tunisia and North Afric ...
, Tunisia *
Biskra Oasis Biskra ( ar, بسكرة ; ; Latin Vescera) is the capital city of Biskra Province, Algeria. In 2007, its population was recorded as 307,987. Biskra is located in northeastern Algeria, about 248 miles (400 km) from Algiers, 71 miles (115&nbs ...
, Algeria *
Khorezm Oasis Khwarazm (; Old Persian: ''Hwârazmiya''; fa, خوارزم, ''Xwârazm'' or ''Xârazm'') or Chorasmia () is a large oasis region on the Amu Darya river delta in western Central Asia, bordered on the north by the (former) Aral Sea, on the ea ...
, Central Asia * Tafilalt, Morocco *
Seba Oasis Sabha, or Sebha ( ar, سبها, Sebhā), is an oasis city in southwestern Libya, approximately south of Tripoli, Libya, Tripoli. It was historically the capital of the Fezzan region and the Fezzan-Ghadames (French Administration), Military Terri ...
, Sabha, Libya *
Oasis of Ghouta Ghouta ( ar, غُوطَةُ دِمَشْقَ / ALA-LC: ''Ḡūṭat Dimašq'') is a countryside and suburban area in southwestern Syria that surrounds the city of Damascus along its eastern and southern rim. Name Ghouta is the Arabic term (''gh ...
, Syria * Wadi Rum, Jordan * Inaren, Morocco *
Gafsa Oases Gafsa Oases (Arabic: واحة قفصة, French: ''Oasis de Gafsa'') is a cluster of oasis sites (Sakdoud, Ksar, Lela, Gafsa and El Guettar) in southwestern Tunisia, near the northern edge of the Sahara Desert. The Gafsa Oases were known to the an ...
, Tunisia * Ghout Oasis, Algeria * Crescent Lake,
Dunhuang Dunhuang () is a county-level city in Northwestern Gansu Province, Western China. According to the 2010 Chinese census, the city has a population of 186,027, though 2019 estimates put the city's population at about 191,800. Dunhuang was a major ...
, China * Hexi Corridor oases, China * Wadi Bani Khalid, Oman * Liwa Oasis, United Arab Emirates *
Chebika Oasis Chebika is the name of: * Chebika, Tozeur, a village and oasis in Tozeur Governorate, Tunisia * Chebika, Kairouan Chebika, Kairouan is a town in the Kairouan Governorate, Tunisia ) , image_map = Tunisia location (orthographic pro ...
, Tunisia * Ein Gedi, Israel * Krupaj Springs, Serbia * Turfan Oasis, China


New World dryland systems with oasis-like attributes

*
Huacachina Huacachina is a village built around a small oasis and surrounded by sand dunes in southwestern Peru. It is about five kilometers from the city of Ica in the Ica District of Ica Province. The oasis was introduced as a feature on the back of the 5 ...
, Peru *
Quitobaquito Quitobaquito, also known as Quitobaquita or Quitovaquita is a populated place situated in Pima County, Arizona, United States. Its current name became official in 1917 as a result of a decision by the Board on Geographic Names The United State ...
, Organ Pipe Cactus National Monument, Arizona * Kitowok, Sonora, Mexico *
Fish Springs National Wildlife Refuge Fish Springs National Wildlife Refuge is at the southern end of the Great Salt Lake Desert, part of the Great Basin in Juab County, Utah, United States. The Refuge is managed by the United States Fish and Wildlife Service. As an oasis in the Grea ...
in Utah, United States *
Havasu Falls Havasu Falls (Havasupai: Havasuw Hagjahgeevma) is a waterfall of Havasu Creek, located in the Grand Canyon, Arizona, United States. It is within Havasupai tribal lands. Geography Havasu Falls is located from Supai. It is the more famous an ...
, Grand Canyon, Arizona * Cuatro Ciengas basin, Chihuahuan desert, Mexico *
Oasis Spring Ecological Reserve In ecology, an oasis (; ) is a fertile area of a desert or semi-desert environment'ksar''with its surrounding feeding source, the palm grove, within a relational and circulatory nomadic system.” The location of oases has been of critical imp ...
, Salton Sea, California


Gallery of oases


See also

* – the world's largest irrigation project; developed in Libya to connect cities with fossil water. * * * * * * * * * Lençóis Maranhenses National Park (Brazil) *
Great Green Wall (disambiguation) Great Green Wall is the name of three tree-planting initiatives: * Great Green Wall (Africa) * Great Green Wall (China) The Great Green Wall, officially known as the Three-North Shelter Forest Program (), also known as the Three-North Shelterbelt ...
*
Aflaj Irrigation Systems of Oman The Aflaj Irrigation Systems of Oman are ancient water channels from 500 AD located in the regions of Dakhiliyah, Sharqiyah and Batinah. However, they represent a type of irrigation system as old as 5000 years in the region named as Qanat or Ka ...
* Palmeral of Elche * Fog oasis (South America)


References


Bibliography

*


External links

* {{Authority control Lacustrine landforms Waystations