TheTurpan water system, also called theTurfan kārēz system, is used forwater supply via a vertical tunnel in theTurpan Depression ofXinjiang,China. "Karez" (lit. 'well') is a word in the localUyghur language that is derived from the word in thePersian language for the system from which it is derived: the 3000-year-oldqanāt.[1] Turpan has theTurpan Karez Paradise (aProtected Area of the People's Republic of China), which is dedicated to demonstrating its karez water system, as well as exhibiting other historical artifacts.
Turpan's karez well system was crucial in Turpan's development as an important oasis stopover on theSilk Road, which skirted the barren and hostileTaklamakan Desert.[2]
Turpan's karez water system is made up of ahorizontal series of vertically dugwells that are then linked by underground watercanals to collect water from thewatershedsurface runoff from the base of theTian Shan Mountains and the nearbyFlaming Mountains. The canals channel the water to the surface, taking advantage of the current provided by thegravity of the downwardslope of the Turpan Depression. The canals are mostly underground to reduce waterevaporation and to make the slope long enough to reach far distances being only gravity fed.[3]
The system has wells,dams and underground canals built to store the water and control the amount of water flow. Vertical wells are dug at various points to tap into thegroundwater flowing down sloping land from the source, the mountainrunoff. The water is then channeled through underground canals dug from the bottom of one well to the next well and then to the desired destination. Turpan's karezirrigation system of special connected wells is believed to be of indigenous origin in China, perhaps combined with technology arriving from more western regions.[3][4]
InXinjiang, the greatest number of karez wells are in theTurpan Depression, where today there remain over 1100 karez wells and channels having a total length of over 5,000 kilometres (3,100 mi). The local geography makes karez wells practical for agricultural irrigation and other uses. Turpan is located in the second deepest geographicaldepression in the world, with over 4,000 km2 (1,500 sq mi) of land belowsea level and with soil that forms a sturdybasin.[3] Water naturally flows down from the nearby mountains during the rainy season in an underground current to the low depression basin under the desert. The Turpan summer is very hot and dry with periods of wind and blowing sand.[citation needed]
Ample water was crucial to Turpan, so that the oasis city could service the manycaravans on the Silk Route resting there near a route skirting theTaklamakan Desert. The caravans includedmerchant traders andmissionaries with their armed escorts, animals including camels, sometimes numbering into the thousands, along with camel drivers, agents and other personnel, all of whom might stay for a week or more. The caravans needed pastures for their animals, resting facilities, tradingbazaars for conducting business and replenishment of food and water.[2]
Karez wells in the Turfan area are on the UNESCO World Heritage Sites Tentative List for China.[5]
There are 20,000 glaciers in Xinjiang – nearly half of all the glaciers in China. The water from the glaciers via the underground channels has provided a stable water source year round, independent of season, for thousands of years.[1] But since the 1950s, Xinjiang's glaciers have retreated by between 21 percent to 27 percent due toglobal warming, threatening the agricultural productivity of the region.[6]
