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| Sichuan Basin | |
|---|---|
| Red Basin | |
 Sichuan Basin landscape inZitong County | |
 Map ofChina with Sichuan Basin highlighted | |
| Length | 500 km (310 mi) |
| Width | 400 km (250 mi) |
| Area | 229,500 km2 (88,600 sq mi) |
| Geography | |
| Country | China |
| Provinces | Sichuan,Chongqing |
| Region | Southwest China |
| Coordinates | 30°30′N105°30′E / 30.500°N 105.500°E /30.500; 105.500 |
TheSichuan Basin (Chinese:四川盆地;pinyin:Sìchuān Péndì), formerly transliterated as theSzechwan Basin, sometimes called theRed Basin, is alowland region in southwesternChina. It is surrounded bymountains on all sides and is drained by the upperYangtze River and its tributaries. The basin is anchored byChengdu, the capital ofSichuan province, in thewest, and thedirect-administered municipality ofChongqing in theeast. Due to its relative flatness and fertile soils, it is able to support a population of more than 100 million. In addition to being a dominant geographical feature of the region, the Sichuan Basin also constitutes a cultural sphere that is distinguished by its own unique customs,cuisine anddialects. It is famous for its rice cultivation and is often considered the breadbasket of China. In the 21st century its industrial base is expanding with growth in the high-tech, aerospace, andpetroleum industries.
The Sichuan Basin is an expansive 229,500 km2 (88,600 sq mi) lowland region in China that is surrounded by upland regions and mountains.[1] Much of the basin is covered in hilly terrain. The basin covers the eastern third ofSichuan Province and the western half of ChongqingMunicipality.[citation needed]
The westernmost section of the Sichuan Basin is theChengdu Plain, occupied byChengdu, provincial capital of Sichuan. The Chengdu Plain is largelyalluvial, formed by theMin River and other riversfanning out when entering the basin from the northwest. This flat region is separated from the rest of the basin by theLongquan Mountains. The central portions of the Sichuan Basin are generally rolling, covered by low hills,eroded remnants of the uplifted Sichuan Basin floor. In some parts of the extreme northern Basin and inWeiyuan County in the southwest, there are ancient dome-shaped low mountains in their own right.[2] TheJialing River enters from the north and flows across the entire width of the Sichuan Basin to meet the Yangtze at Chongqing. Northeast of Chongqing, the Yangtze cuts an outlet through the mountains at the eastern edge of the basin known as theThree Gorges. Other significant rivers almost wholly within the Sichuan Basin include theTuo River, theFu River, and theQu River.[3]
Due to the surrounding mountains, the Sichuan Basin often experiencesfog andsmog as a result oftemperature inversion caused by the basin's convective layer beingcapped by a layer of air moving east across the Tibet Plateau.[1]
A moist, often overcast, four-season climate dominates the basin, with cool to mildwinters occasionally experiencing frost, and hot, very humidsummers. The intensity of summer varies rather widely throughout the basin, depending on location. Generally, the climate is warmer and wetter in the eastern parts of the Sichuan Basin.[4] The basin's climate is classified ashumid subtropical under Koppen classification.[citation needed]The entirety of the Sichuan Basin is drained by theYangtze River and its tributaries.[4] The main stem of the Yangtze, theJinsha River, enters the basin in the south atYibin where it meets theMin River, which enters the basin from the northwest atDujiangyan City and flows southerly to meet the Jinsha at Yibin where together they form the Yangtze in name. TheDadu River enters from the west and joins the Min atLeshan.
The Sichuan Basin forms the rigid northwest edge of theYangtzetectonic plate. The Yangtze Plate's complex relationship with the surroundingEurasian Plate is evidenced at its margins.[5]Orogeny formed by theIndian Plate's collision with Eurasia has compressed against the Sichuan Basin's western edge, most notably along theLongmenshan Fault, the epicenter of the2008 Sichuan Earthquake. The basin's rigidity withstands much of the Tibetan Plateau's eastern movement, but dramaticfolds have formed within the Yangtze Plate along the Sichuan Basin's eastern edges. Here, ancient faults interact with theDaba Mountains, themselves a result of pressure between the Yangtze and Eurasian Plates in a perpendicular direction.[6]
Until 6 million years ago, a large lake filled the Sichuan Basin.[4] The basin's soils today are largely exposed red sandstone,[1] leading to the "Red Basin" nickname for the region. The Sichuan Basin's well preservedJurassic layers have proven valuable topaleontology, such of those of theShaximiao Formation, nearZigong, which preserves abundant remains of dinosaurs and other prehistoric animals.[7]
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Originally, the Sichuan Basin was covered by theSichuan Basin evergreen broadleaf forests. With human settlement, agriculture has taken root across most of the fertile basin and reduced the original forest to small patches on hills and mountains includingMount Emei.[8] The extensive ridges in the eastern Sichuan Basin preserve elements of the original forests.[3] A greater variety of natural landscapes and wildlife have been at least partially preserved in the mountains surrounding the basin where human settlement has been less intensive. The natural ecosystems of these mountains have been classified by theWorld Wide Fund for Nature as theQionglai-Minshan conifer forests to northwest and theDaba Mountains evergreen forests to the northeast and east.[9][10]
Previously only known in fossils and thought to be extinct, theDawn Redwood (Metasequoia glyptostroboides) was rediscovered in 1943 in the hillyLichuan County, on the eastern mountain fringe of the Sichuan Basin.[11] The Dawn Redwood is distinctive because it is a deciduous conifer.[citation needed]
Relative to the areas surrounding the upperYellow River and theNorth China Plain, the Sichuan Basin has played a peripheral role in the development ofChinese civilization. Due to the fertile agricultural characteristics of the basin, numerous cultures developed prior to integration with ancient Chinese dynasties.[3] No written records exist from early cultures in the Sichuan Basin. What little is known about the area is from when contact was made with Shang and Zhou and from the archaeological site ofSanxingdui.[12] Predominant among the known ancient cultures was theShu State that was independent from the Zhou until it was strategically conquered by theQin in 316 BCE during theWarring States period.[13] The Sichuan Basin was integrated into Imperial China underQin dynasty for whom it was an important agricultural resource.[12]
During the period of theThree Kingdoms, the Sichuan Basin was at the centre of another independentShu State, until it was reunified with China in the 3rd century CE by theJin dynasty.[13] Around this time the basin's population is estimated to have been 1 million, withChengdu the leading city. After the collapse of theTang dynasty in 907, the Sichuan Basin became home to a thirdShu state, this time lasting only two decades.[13] During successive Chinese dynasties, the Sichuan Basin was firmly integrated withGreater China. Mass migration occurred during theMing dynasty as the basin became one of the primary rice-producing regions of China. The basin's population fell sharply in the 17th century due todevastation caused by famine, war, and possible genocide.[14] After this time, the basin was repopulated with emigrants from China, further assimilating the unique cultures and peoples inhabiting the basin.[15] During theSecond Sino-Japanese War when much of Eastern China was occupied by Japanese forces,Chongqing in the Sichuan Basin served as theRepublic of China's capital.[13]
Owing to its vast fertile plains, the Sichuan Basin has long supported a high concentration of human population.[1] The major population centres of Chengdu and Chongqing have flourished with their hinterlands providing staples such as rice, wheat, and barley. Irrigation in the western part of the basin has been controlled for over two millennia by the monumentalDujiangyan irrigation system, where theMin River enters.[16] The region has been known as a majorbreadbasket of China, especially in the 20th century during times of war.[3] Sichuan Basin also became a major focus of industrial development duringMao'sGreat Leap Forward. In more recent times, the Sichuan Basin and the corridor between Chengdu and Chongqing have become developed as an economic centre known as theChengdu-Chongqing Economic Circle. This area is mostly coterminous with the basin; it is part of a branding scheme by the Chinese government to attract investment to the area. Chemical, textile, electronic, aerospace, and food industries have all been developed as part of this Chengyu area.[3] Another emerging industry in the basin is thepetroleum industry, currently exploring and extracting from oil reserves locked under the eastern parts of the basin.[17]
While population growth stagnated during the Great Leap Forward, it has since recovered. Today, the basin has a population of approximately 100 million.[3] Administratively, the entire basin was part of Sichuan province until Chongqingwas separated into a provincial-level municipality in 1997. In addition to Chengdu and Chongqing, significant cities found within the Sichuan Basin includeGuangyuan,Mianyang,Deyang,Nanchong,Guang'an,Dazhou,Ya'an,Meishan,Leshan,Ziyang,Suining,Neijiang,Zigong,Yibin, andLuzhou. The former cities ofFuling andWanzhou are now considered districts within Chongqing, but maintain their status as separate urban centres along the Yangtze.[18]
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Some unique elements of Sichuanese culture remain in the Basin.Sichuanese cuisine today is renowned for its unique flavours and levels of spiciness.[16] TheSichuanese branch ofMandarin Chinese is barely mutually intelligible with Standard Mandarin and originated in the Sichuan Basin. Today, Sichuanese is spoken throughout eastern Sichuan province, Chongqing, southernShaanxi, and westernHubei.
While transportation across the Sichuan Basin has been facilitated by relative flatness, access to and from the basin has long been a challenge.[3] Chinese poetLi Bai once claimed that the road to Sichuan was "harder than the road to heaven".[19] Until the construction of theThree Gorges Dam, the Yangtze River was the primary transportation corridor. Connecting the basin with the Yellow River valley to the north, the 4th century BCEShu Roads were an engineering feat for their time.[20] Most famously, the semi-legendaryStone Cattle Road is said to have been utilized by theQin to first conquer the Sichuan Basin in 316 BC.[13]
Transportation to the west from Sichuan has proven to be an even greater challenge, with steep mountains and deep valleys hindering movement. Nevertheless, the Sichuan Basin has played a role as a stopover on thesouthern Silk Road and provided the most direct route between India and China. The southern trade route toTibet also passed through the basin, eventually crossingKham and theDerge Kingdom to the west.[21] TheLong March passed to the west of Sichuan Basin in 1935 with great difficulty.[13]
In the 20th century, the Sichuan Basin was connected to the rest of China by railways. TheChengyu Railway, completed in 1952, connected Chengdu and Chongqing within the basin.[22] The first rail link to outside the basin was theBaoji–Chengdu Railway, completed in 1961 to connect withShaanxi province across theQin Mountains to the north.[23] The basin was also connected with Yunnan to the southwestin 1970, Hubei to the eastin 1979, and Guizhou to the southin 2001. In the 21st century, manyhigh-speed rail lines have been built or planned for the Sichuan Basin including theChengdu-Guiyang andChengdu-Xi'an lines.[24][25]
Highway construction within Sichuan Basin intensified in the 21st century.Expressways through the basin include theG5,G42,G50,G65,G75,G76,G85, andG93.[26] All expressways that connect the Sichuan Basin with other parts of China have been designed to utilize a series of tunnels and bridges to cross the mountainous surrounding terrain. Notable examples include the 18 km (11 mi) longZhongnanshan Tunnel through the Qin Mountains to the north and the 500 m (1,600 ft) highSidu River Bridge through the Wu Mountains to the east.[citation needed]
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