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72-477: There was one section of more than 106 kilometres (66 mi), constructed with qanat technology. In this special case, nearly all the shafts were diagonal at 45–60 degrees, with stairs to the real water channel inside the mountain. The line went along steep slopes and collected water from sources around the area. The first visitor who rode along the "Kanatir" was U. J. Seetzen in 1805. There are gradients of 0.3 metres per mile (0.2 m/km; 1.0 ft/mi) for

144-499: A crew of four workers can excavate a horizontal length of 40 m (130 ft) per day. When the vertical shaft reaches 40 m (130 ft), they can excavate only 20 meters horizontally per day and at 60 m (200 ft) in depth this drops below 5 horizontal meters per day. In Algeria, a common speed is just 2 m (6.6 ft) per day at a depth of 15 m (49 ft). Deep, long qanats (which many are) require years and even decades to construct. The excavated material

216-527: A critical situation in the water supply system. Still, kahrezes are the main source of potable and irrigation water for the community. Desert climate The desert climate or arid climate (in the Köppen climate classification BWh and BWk ) is a dry climate sub-type in which there is a severe excess of evaporation over precipitation . The typically bald, rocky, or sandy surfaces in desert climates are dry and hold little moisture, quickly evaporating

288-766: A few instances), dry summers, though summers are not typically as hot as hot desert climates. Unlike hot desert climates, cold desert climates tend to feature cold, dry winters. Snow tends to be rare in regions with this climate. The Gobi Desert in northern China and Mongolia is one example of a cold desert. Though hot in the summer, it shares the freezing winters of the rest of Inner Asia . Summers in South America's Atacama Desert are mild, with only slight temperature variations between seasons. Cold desert climates are typically found at higher altitudes than hot desert climates and are usually drier than hot desert climates. Cold desert climates are typically located in temperate zones in

360-452: A qanat is stored in a reservoir, typically with night flow stored for daytime use. An ab anbar is an example of a traditional Persian qanat-fed reservoir for drinking water. The qanat system has the advantage of being resistant to natural disasters such as floods, and to deliberate destruction in war. Furthermore, it is almost insensitive to the levels of precipitation, delivering a flow with only gradual variations from wet to dry years. From

432-416: A qanat system had to be carefully situated, to make best use of the slow flow of water. In Iran, there were subterranean mills at Yazd and Boshruyeh ; at Taft and Ardestan mills were placed at the outflow from the qanat, before irrigation of the fields. Qanats used in conjunction with a wind tower can provide cooling as well as a water supply. A wind tower is a chimney-like structure positioned above

504-433: A side shaft through the easily penetrated sandstone (presumably in the direction of greatest water seepage) into the hill of Ayn-Manâwîr (also written Ayn-Manawir  [ fr ] to allow collection of additional water. After this side shaft had been extended, another vertical shaft was driven to intersect the side shaft. Side chambers were built, and holes bored into the rock—presumably at points where water seeped from

576-513: A small dam at the end. The width is approximately 60 cm (24 in), but the height ranges from 5 to 9 meters; it is likely that the qanat was deepened to enhance seepage when the water table dropped (as is also seen in Iran). From there the water was used to irrigate fields. There is another instructive structure located at the Kharga Oasis. A well that apparently dried up was improved by driving

648-400: A sufficient flow is available to justify construction. If these prerequisites are met, the route is laid out aboveground. Equipment must be assembled. The equipment is straightforward: containers (usually leather bags), ropes, reels to raise the container to the surface at the shaft head, hatchets and shovels for excavation, lights, and spirit levels or plumb bobs and string. Depending upon

720-518: A sustainability perspective, qanats are powered only by gravity and thus have low operation and maintenance costs. Qanats transfer fresh water from the mountain plateau to the lower-lying plains with saltier soil. This helps to control soil salinity and prevent desertification . The qanat should not be confused with the spring-flow tunnel typical to the mountainous area around Jerusalem . Although both are excavated tunnels designed to extract water by gravity flow, there are crucial differences. Firstly,

792-507: A ten-meter width, with length reckoned by the size of plot that the available water will irrigate. The qanats are called kariz in Dari (Persian) and Pashto and have been in use since the pre-Islamic period. It is estimated that more than 9,370 karizes were in use in the 20th century. The oldest functional kariz which is more than 300 years old and 8 kilometers long is located in Wardak province and

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864-875: Is a system for transporting water from an aquifer or well to the surface through an underground aqueduct ; the system originated approximately 3,000 years ago in Iran . The function is essentially the same across the Middle East and North Africa , but the system operates under a variety of regional names: qanat or kārīz in Iran, karez in Afghanistan and Pakistan , foggara in Algeria , qanat in Malta , khettara in Morocco , falaj in Oman and

936-552: Is determined. The precipitation threshold (in millimetres) involves first multiplying the average annual temperature in °C by 20, then adding 280 if 70% or more of the total precipitation is in the high-sun summer half of the year (April through September in the Northern Hemisphere , or October through March in the Southern), or 140 if 30–70% of the total precipitation is received during the applicable period, or 0 if less than 30% of

1008-536: Is seen in sections of Africa and Arabia . During colder periods of the year, night-time temperatures can drop to freezing or below due to the exceptional radiation loss under the clear skies. However, temperatures rarely drop far below freezing under the hot subtype. Hot desert climates can be found in the deserts of North Africa such as the wide Sahara Desert , the Libyan Desert or the Nubian Desert ; deserts of

1080-559: Is still providing water to nearly 3,000 people. Many of these ancient structures were destroyed during the Soviet–Aghan War and the War in Afghanistan . Maintenance has not always been possible. The cost of labour has become very high, and maintaining the kariz structures is no longer possible. Lack of skilled artisans who have the traditional knowledge also poses difficulties. A number of

1152-461: Is supported by the historian Albert T. Olmstead . There are four main oases in the Egyptian desert. The Kharga Oasis is one that has been extensively studied. There is evidence that as early as the second half of the 5th century BCE water brought in qanats was being used. The qanats were excavated through water-bearing sandstone rock, which seeps into the channel, with water collected in a basin behind

1224-403: Is used as an isotherm so that a location with a BW type climate with the appropriate temperature above this isotherm is classified as "hot arid subtype" ( BW h ), and a location with the appropriate temperature below the isotherm is classified as "cold arid subtype" ( BW k ). Most desert/arid climates receive between 25 and 200 mm (1 and 8 in) of rainfall annually, although some of

1296-403: Is used, has more than one qanat. Fields and gardens are located both over the qanats a short distance before they emerge from the ground and below the surface outlet. Water from the qanats define both the social regions in the city and the layout of the city. The water is freshest, cleanest, and coolest in the upper reaches, and more prosperous people live at the outlet or immediately upstream of

1368-453: Is usually transported by means of leather bags up the vertical shafts. It is mounded around the vertical shaft exit, providing a barrier that prevents windblown or rain driven debris from entering the shafts. These mounds may be covered to provide further protection to the qanat. From the air, these shafts look like a string of bomb craters. The qanat's water-carrying channel must have a sufficient downward slope that water flows easily. However

1440-644: Is very common for a qanat to start below the foothills of mountains, where the water table is closest to the surface. From this source, the qanat tunnel slopes gently downward, slowly converging with the steeper slope of the land surface above, and the water finally flows out above ground where the two levels meet. To connect a populated or agricultural area with an aquifer, qanats must often extend for long distances. Qanats are sometimes split into an underground distribution network of smaller canals called kariz. Like qanats, these smaller canals are below ground to avoid contamination and evaporation. In some cases water from

1512-894: The Horn of Africa such as the Danakil Desert or the Grand Bara Desert ; deserts of Southern Africa such as the Namib Desert or the Kalahari Desert ; deserts of West Asia such as the Arabian Desert , or the Syrian Desert ; deserts of South Asia such as Dasht-e Lut and Dasht-e Kavir of Iran or the Thar Desert of India and Pakistan; deserts of the United States and Mexico such as

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1584-701: The Indian Subcontinent , southwestern Africa, interior Australia, the Southwestern United States , northern Mexico , sections of southeastern Spain , the coast of Peru , and Chile . This makes hot deserts present in every continent except Antarctica. At the time of high sun (summer), scorching, desiccating heat prevails. Hot-month average temperatures are normally between 29 and 35 °C (84 and 95 °F), and midday readings of 43–46 °C (109–115 °F) are common. The world's absolute heat records, over 50 °C (122 °F), are generally in

1656-857: The Indian subcontinent for a long time. Cotton appears in the Inquiry into Plants by Theophrastus and is mentioned in the Laws of Manu . As transregional trade networks expanded and intensified, cotton spread from its homeland to India and into the Middle East. One theory is that the qanat was developed to irrigate cotton fields, first in what is now Iran, where it doubled the amount of available water for irrigation and urban use. Because of this, Persia enjoyed larger surpluses of agricultural products, thus increasing urbanization and social stratification. The qanat technology subsequently spread from Persia westward and eastward. In

1728-759: The Mojave Desert , the Sonoran Desert or the Chihuahuan Desert ; deserts of Australia such as the Simpson Desert or the Great Victoria Desert and many other regions. In Europe , the hot desert climate can only be found on southeastern coast of Spain as well as small inland parts of southeastern, especially parts of the Tabernas Desert . Hot deserts are lands of extremes: most of them are among

1800-521: The Sahara Desert such as Kufra , Libya , record an even drier 0.86 mm (0.034 in) of rainfall annually. The official weather station in Death Valley , United States reports 60 mm (2.4 in) annually, but in 40 months between 1931 and 1934 a total of just 16 mm (0.63 in) of rainfall was measured. To determine whether a location has an arid climate, the precipitation threshold

1872-643: The United Arab Emirates , and uyūn in Saudi Arabia , etc. The largest extant and functional qanat systems are located in Afghanistan, Algeria, Iran, Oman , Pakistan, and the oases of the Turfan region in Xinjiang , Northwestern China . This is a system of water supply that allows water to be transported over long distances in hot dry climates without losing much of the water to evaporation . The system has

1944-531: The groundwater . Much of the population of Iran and other arid countries in North Africa and West Asia historically depended upon the water from qanats; many populated areas are close to the areas where qanats are possible. Common variants of qanat in English include kanat , khanat , kunut , kona , konait , ghanat , ghundat . Qanāh ( قناة ) is an Arabic word that means "channel". In Persian ,

2016-445: The province of Khorasan have been recorded with vertical shafts of up to 275 m (902 ft). The vertical shafts support construction and maintenance of the underground channel as well as air interchange. Deep shafts require intermediate platforms to facilitate the process of removing soil. The construction speed depends on the depth and nature of the ground. If the earth is soft and easy to work, at 20 m (66 ft) depth

2088-635: The 30s and 40s latitudes, usually in the leeward rain shadow of high mountains, restricting precipitation from the westerly winds. An example of this is the Patagonian Desert in Argentina, bounded by the Andes ranges to its west. In the case of Central Asia, mountains restrict precipitation from the eastern monsoon . The Kyzyl Kum , Taklamakan and Katpana Desert deserts of Central Asia are other significant examples of BWk climates. The Ladakh region and

2160-563: The Iranian qanat. The foggara is dug into the foothills of a fairly steep mountain range such as the eastern ranges of the Atlas Mountains . Rainfall in the mountains enters the aquifer and moves toward the Saharan region to the south. The foggara, 1 to 3 km (0.62 to 1.9 mi) in length, penetrates the aquifer and collects water. Families maintain the foggara and own the land it irrigates over

2232-404: The advantage of being resistant to natural disasters such as floods and to deliberate destruction in war. Furthermore, it is almost insensitive to the levels of precipitation, delivering a flow with only gradual variations from wet to dry years. Karez are constructed as a series of well-like vertical shafts, connected by a gently sloping tunnel. This taps into underground water and delivers it to

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2304-500: The already little rainfall they receive. Covering 14.2% of Earth's land area, hot deserts are the second-most common type of climate on Earth after the Polar climate . There are two variations of a desert climate according to the Köppen climate classification : a hot desert climate ( BWh ), and a cold desert climate ( BWk ). To delineate "hot desert climates" from "cold desert climates", a mean annual temperature of 18 °C (64.4 °F)

2376-565: The arid coastal desert of Peru, a technology of water supply similar to that of the qanats, called puquios , was developed. Most archaeologists believe that the puquios are indigenous and date to about 500 CE, but a few believe they are of Spanish origin, brought to the Americas in the 16th century. Puquios were still in use in the Nazca region in the 21st century. In arid and semi-arid regions, owing to high evaporation, transportation routes were in

2448-900: The city of Leh in the Great Himalayas in India also have a cold desert climate. In North America, the cold desert climate occurs in the drier parts of the Great Basin Desert and the Bighorn Basin in Big Horn and Washakie County in Wyoming . The Hautes Plaines , located in the northeastern section of Morocco and in Algeria , is another prominent example of a cold desert climate. In Europe , this climate only occurs in some inland parts of southeastern Spain, such as in Lorca . Polar climate desert areas in

2520-474: The cool tunnel walls/water and by the transfer of latent heat of evaporation as water evaporates into the air stream. In dry desert climates this can result in a greater than 15 °C reduction in the air temperature coming from the qanat; the mixed air still feels dry, so the basement is cool and only comfortably moist (not damp). Wind tower and qanat cooling have been used in desert climates for over 1,000 years. By 400 BCE, Persian engineers had mastered

2592-437: The destination to which the water will be delivered into the soil and works toward the source (the test well). Vertical shafts are excavated along the route, separated at a distance of 20–35 m (66–115 ft). The separation of the shafts is a balance between the amount of work required to excavate them and the amount of effort required to excavate the space between them, as well as the ultimate maintenance effort. In general,

2664-414: The downward gradient must not be so great as to create conditions under which the water transitions between supercritical and subcritical flow . If this occurs, the waves that result can result in severe erosion that can damage or destroy the qanat. The choice of the slope is a trade off between erosion and sedimentation. Highly sloped tunnels are subject to more erosion as water flows at a higher speed. On

2736-464: The effort. There were still functional qanat systems in 2009. American forces were reported to have unintentionally destroyed some of the channels during expansion of a military base, creating tensions between them and the local community. Some of these tunnels were used to store supplies, and to move men and equipment underground. Qanats have been preserved in Armenia in the community of Shvanidzor , in

2808-453: The foggara. The moist air of the agricultural area is drawn into the foggara in the opposite direction to the water run-off. In the foggara it condenses on the tunnel walls and the air passes out of the vertical shafts. This condensed moisture is available for reuse. Qanat irrigation technology was introduced to Egypt by the Achaemenid king Darius I during his reign of 522 BCE-486 BCE, which

2880-447: The form of qanats, which led groundwater to consumption areas along underground tunnels. In the long run, the qanat system is not only economical but also sustainable for irrigation and agricultural purposes.… The ground water flow was known to depend on grain size of sediments, and, therefore, the tunnels in qanats are filled in with coarser material than the surrounding host geological formations. The qanats are constructed mainly along

2952-849: The gradient is steeper, underground waterfalls may be constructed with appropriate design features (usually linings) to absorb the energy with minimal erosion. In some cases the water power has been harnessed to drive underground mills . If it is not possible to bring the outlet of the qanat out near the settlement, it is necessary to run a jub or canal overground. This is avoided when possible to limit pollution, warming and water loss due to evaporation. The vertical shafts may be covered to minimize blown-in sand. The channels of qanats must be periodically inspected for erosion or cave-ins, cleaned of sand and mud and otherwise repaired. For safety, air flow must be assured before entry. Some damaged qanats have been restored. To be sustainable, restoration needs to take into account many nontechnical factors beginning with

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3024-595: The hot deserts, where the heat potential can be the highest on the planet. This includes the record of 56.7 °C (134.1 °F) in Death Valley , which is currently considered the highest temperature recorded on Earth . Some deserts in the tropics consistently experience very high temperatures all year long, even during wintertime. These locations feature some of the highest annual average temperatures recorded on Earth, exceeding 30 °C (86 °F), up to nearly 35 °C (95 °F) in Dallol, Ethiopia . This last feature

3096-444: The hottest, the driest, and the sunniest places on Earth because of nearly constant high pressure; the almost permanent removal of low-pressure systems, dynamic fronts, and atmospheric disturbances; sinking air motion; dry atmosphere near the surface and aloft; the exacerbated exposure to the sun where solar angles are always high makes this desert inhospitable to most species. Cold desert climates ( BWk ) usually feature hot (or warm in

3168-427: The house; of its four openings, the one opposite the wind direction is opened to move air out of the house. Incoming air is pulled from a qanat below the house. The air flow across the vertical shaft opening creates a lower pressure (see Bernoulli effect ) and draws cool air up from the qanat tunnel, mixing with it. The air from the qanat is drawn into the tunnel at some distance away and is cooled both by contact with

3240-468: The ice was stored in yakhchals—specially designed, naturally cooled refrigerators. A large underground space with thick insulated walls was connected to a qanat, and a system of windcatchers or wind towers was used to draw cool subterranean air up from the qanat to maintain temperatures inside the space at low levels, even during hot summer days. As a result, the ice melted slowly and was available year-round. Qanats (designated foggaras in Algeria ) are

3312-450: The large farmers are abandoning their kariz which has been in their families sometimes for centuries, and moving to tube and dug wells backed by diesel pumps. However, the government of Afghanistan was aware of the importance of these structures and all efforts were made to repair, reconstruct and maintain (through the community) the kariz. The Ministry of Rural Rehabilitation and Development along with national and international NGOs made

3384-423: The lower reaches are the most likely to see substantial reductions in flow. Traditionally qanats are built by a group of skilled laborers, muqannīs , with hand labor. The profession historically paid well and was typically handed down from father to son. The critical, initial step in qanat construction is identification of an appropriate water source. The search begins at the point where the alluvial fan meets

3456-571: The main course of the Ziz River and its subsequent impact on local water tables is said to be one of the many reasons for the loss of half of the khettara. The black berbers ( haratin ) of the south were the hereditary class of qanat diggers in Morocco who build and repair these systems. Their work was hazardous. The foggara water management system in Tunisia, used to create oases, is similar to that of

3528-538: The most consistently hot areas of Central Australia , the Sahel and Guajira Peninsula can be, due to extreme potential evapotranspiration , classed as arid with the annual rainfall as high as 430 millimetres or 17 inches. Although no part of Earth is known for certain to be rainless, in the Atacama Desert of northern Chile, the average annual rainfall over 17 years was only 5 millimetres (0.20 in). Some locations in

3600-432: The mountains or foothills; water is more abundant in the mountains because of orographic lifting , and excavation in the alluvial fan is relatively easy. The muqannīs follow the track of the main water courses coming from the mountains or foothills to identify evidence of subsurface water such as deep-rooted vegetation or seasonal seeps. A trial well is then dug to determine the depth of the water table and determine whether

3672-449: The neighborhood, gardens and fields. The streets normally parallel the jubs and their lateral branches. As a result, the cities and towns are oriented consistent with the gradient of the land; this is a practical response to efficient water distribution over varying terrain. The lower reaches of the canals are less desirable for both residences and agriculture. The water grows progressively more polluted as it passes downstream. In dry years

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3744-413: The oases in the 10th century and the residents embraced Islam. The water is metered to the various users through the use of distribution weirs that meter flow to the various canals, each for a separate user. The humidity of the oases is also used to supplement the water supply to the foggara. The temperature gradient in the vertical shafts causes air to rise by natural convection, causing a draft to enter

3816-403: The origin of the qanat was a well that was turned into an artificial spring. In contrast, the origin of the spring-flow tunnel was the development of a natural spring to renew or increase flow following a recession of the water table. Secondly, the shafts essential for the construction of qanats are not essential to spring-flow tunnels. A typical town or city in Iran, and elsewhere where the qanat

3888-418: The other hand, less sloped tunnels need frequent maintenance due to the problem of sedimentation. A lower downward gradient also contributes to reducing the solid contents and contamination in water. In shorter qanats the downward gradient varies between 1:1000 and 1:1500, while in longer qanats it may be almost horizontal. Such precision is routinely obtained with a spirit level and string. In cases where

3960-512: The outlet. When the qanat is still below ground, the water is drawn to the surface via wells or animal driven Persian wells . Private subterranean reservoirs could supply houses and buildings for domestic use and garden irrigation as well. Air flow from the qanat is used to cool an underground summer room ( shabestan ) found in many older houses and buildings. Downstream of the outlet, the water runs through surface canals called jubs ( jūbs ) which run downhill, with lateral branches to carry water to

4032-659: The process of selecting the qanat to be restored. In Syria, three sites were chosen based on a national inventory conducted in 2001. One of them, the Drasiah qanat of Dmeir , was completed in 2002. Selection criteria included the availability of a steady groundwater flow, social cohesion and willingness to contribute of the community using the qanat, and the existence of a functioning water-rights system. The primary applications of qanats are for irrigation, providing cattle with water, and drinking water supply. Other applications include watermills, cooling and ice storage. Watermills within

4104-581: The qanat (locally khettara ) is also used. On the margins of the Sahara Desert , the isolated oases of the Draa River valley and Tafilalt have relied on qanat water for irrigation since the late 14th century. In Marrakech and the Haouz plain, the qanats have been abandoned since the early 1970s, having dried up. In the Tafilaft area, half of the 400 khettaras are still in use. The 1971 Hassan Adahkil Dam 's build in

4176-419: The qanat. And misreading the soil conditions leads to collapses, which at best require extensive rework and at worst are fatal for the crew. Construction of a qanat is usually performed by a crew of 3–4 muqannīs . For a shallow qanat, one worker typically digs the horizontal shaft, one raises the excavated earth from the shaft and one distributes the excavated earth at the top. The crew typically begins from

4248-617: The remaining substructions were demolished on the plains between Dilli and Dera'a near the Syria-Jordan border . East of Adraha was a 35-metre (115 ft) bridge. The remains of the bridge now can be found on the ground of the new Al Saad Dam located at the eastern suburbs of Dera'a. After a junction point with a side channel from the Muzayrib lake, the underground aqueduct begins. Three water systems have been found near Gadara (Umm Qais). The first and second were built with qanat technology, and

4320-643: The rocks—are evident. David Mattingly reports foggara extending for hundreds of miles in the Garamantes area near Germa in Libya : "The channels were generally very narrow – less than 2 feet wide and 5 high – but some were several miles long, and in total some 600 foggara extended for hundreds of miles underground. The channels were dug out and maintained using a series of regularly spaced vertical shafts, one every 30 feet or so, 100,000 in total, averaging 30 feet in depth, but sometimes reaching 130." In southern Morocco,

4392-450: The shallower the qanat, the closer the vertical shafts. If the qanat is long, excavation may begin from both ends at once. Tributary channels are sometimes also constructed to supplement the water flow. Most qanats in Iran run less than 5 km (3.1 miles), while some have been measured at ≈70 km (43 miles) in length near Kerman . The vertical shafts usually range from 20 to 200 m (66 to 656 ft) in depth, although qanats in

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4464-420: The soil type, qanat liners (usually fired clay hoops) may also be required. Although the construction methods are simple, the construction of a qanat requires a detailed understanding of subterranean geology and a degree of engineering sophistication. The gradient of the qanat must be carefully controlled: too shallow a gradient yields no flow and too steep a gradient will result in excessive erosion, collapsing

4536-454: The source of water for irrigation in large oases like Gourara . The foggaras are also found at Touat (an area of Adrar 200 km from Gourara). The length of the foggaras in this region is estimated to be thousands of kilometers. Although sources suggest that the foggaras may have been in use as early as 200 CE, they were clearly in use by the 11th century after the Arabs took possession of

4608-556: The southern province of Syunik , bordering with Iran. Qanats are named kahrezes in Armenian. There are 5 kahrezes in Shvanidzor. Four of them were constructed before the village was founded. The fifth kahrez was constructed in 2005. Potable water runs through three of them, and two are in poor condition. In the summer, especially in July and August, the amount of water reaches its minimum, creating

4680-426: The surface by gravity, without need for pumping. The vertical shafts along the underground channel are for maintenance purposes, and water is typically used only once it emerges from the daylight point. The qanats still create a reliable supply of water for human settlements and irrigation in hot, arid , and semi-arid climates, but the value of this system is directly related to the quality, volume, and regularity of

4752-431: The technique of storing ice in the middle of summer in the desert. The ice could be brought in during the winters from nearby mountains, but in a more usual and sophisticated method they built a wall in the east–west direction near a yakhchal (ice pit). In winter, the qanat water would be channeled to the north side of the wall, whose shade made the water freeze more quickly, increasing the ice formed per winter day. Then

4824-673: The third was built as a channel along a street. It is believed that all three systems were used, but each at a different period. Beneath the classical city of Adraha was an underground city, and was also part of the aqueduct. The inhabitants of the city collected water by jars on ropes, from the underground channel. Today, however, there is no sign of the "underground city" which was described by Wetzstein in 1860 and G. Schumacher in 1896. [REDACTED] Media related to Gadara Aqueduct at Wikimedia Commons 32°40′51″N 35°52′09″E  /  32.6808°N 35.8691°E  / 32.6808; 35.8691 Qanat A qanat or kārīz

4896-650: The total precipitation is so received there. If the area's annual precipitation is less than half the threshold (50%), it is classified as a BW (desert climate), while 50–100% of the threshold results in a semi-arid climate. Hot desert climates ( BWh ) are typically found under the subtropical ridge in the lower middle latitudes or the subtropics , often between 20° and 33° north and south latitudes. In these locations, stable descending air and high pressure aloft clear clouds and create hot, arid conditions with intense sunshine. Hot desert climates are found across vast areas of North Africa , West Asia , northwestern parts of

4968-478: The tunnel section. The aqueduct starts at a Roman dam in Dilli (al-Dali, also spelled el-Dilli, Eldili, ad-Dili, c. 7 km north of the sub-district residence town of Al-Shaykh Maskin , Izra District , Daraa Governorate , Syria ). From there, this part of the aqueduct line crosses several wadis via five-to-ten-metre-high (15–35 ft) bridges. During the last few decades, more than three kilometres (2 mi) of

5040-533: The valleys where Quaternary sediments are deposited. Qanats are constructed as a series of well -like vertical shafts , connected by a gently sloping tunnel which carries a water canal . Qanats efficiently deliver large amounts of subterranean water to the surface without need for pumping. The water drains by gravity, typically from an upland aquifer , with the destination lower than the source. Qanats allow water to be transported over long distances in hot dry climates without much water loss to evaporation . It

5112-729: The words for "qanat" are kārīz (or kārēz ; كاريز ) and is derived from earlier word kāhrēz ( كاهریز ). The word qanāt ( قنات ) is also used in Persian. Other names for qanat include kahan ( Persian : کهن ); Kahn ( Balochi ); kahriz/kəhriz ( Azerbaijan ); khettara ( Morocco ); Galerías , minas or viajes de agua (Spain); falaj ( Arabic : فلج ) ( United Arab Emirates and Oman ); foggara/fughara ( North Africa ). Alternative terms for qanats in Asia and North Africa are kakuriz , chin-avulz , and mayun . According to most sources, qanat technology

5184-525: Was developed in ancient Iran by the Persians sometime in the early 1st millennium BCE and slowly spread westward and eastward from there. Other sources suggest a Southeast Arabian origin. Analogous systems appear to have been developed independently in China and in South America (specifically, southern Peru ). A cotton species, Gossypium arboreum , is indigenous to South Asia and has been cultivated on

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