BEIJING, Aug. 22 (Xinhua) -- Chinese scientists have pinpointed the sources of four major rivers that flow through China and south Asia, and measured their lengths and size of drainage basins, information that will prove to be invaluable for future environmental research.
The information about the Brahmaputra, Indus, Salween and Irrawaddy rivers was a result of expeditions and satellite photograph analysis by researchers from the Chinese Academy of Sciences (CAS).
Previously, the sources of the four rivers were never clearly designated, and differing accounts regarding their lengths and drainage areas confused researchers for many years due to restrictions of natural conditions and surveying and mapping technologies, said Liu Shaochuang, a researcher with the Institute of Remote Sensing Applications under the CAS.
The four rivers originate on the Qinghai-Tibet Plateau along with the Yangtze, Yellow, Mekong and Ganges rivers, and provide water for about 1.3 billion people, according to Liu.
Liu has worked to locate the sources of the world's largest rivers since the 1990s. He has pinpointed the sources of 15 principal rivers and measured their lengths by using satellite remote-sensing technology and conducting field investigations.
Liu said some of his previous findings have been cited by the U.S. National Geographic Society and the Mekong River Commission.
Liu said the location of the sources of the four rivers will be of great significance for environmental researchers.
He said the determination of the four rivers' sources was based on a principle commonly accepted within the international geographical community: that the source of a river is defined as the longest branch in the river's drainage basin.
To locate the headstreams of the rivers and measure their lengths, Liu's team used remote-sensing images provided by the U.S. Landsat satellite and the French SPOT satellite. These satellites provided his team with high-resolution photos of the Qinghai-Tibet Plateau.
However, Liu and his team still wished to verify the accuracy of the images themselves.
To that end, the institute of the CAS and the National Geomatics Center of China under the National Administration of Surveying, Mapping and Geoinformation formed joint expedition teams to conduct four field investigations between 2007 and 2010.
The result of their analysis and field investigations showed that the Brahmaputra River, called Yarlungzangbo in China, originates on the Angsi Glacier, located on the northern side of the Himalayas in Burang County of China's Tibet Autonomous Region.
The source of Brahmaputra was previously believed to be either on the Chema-yungdung glacier, as proposed by Indian geographer Swami Pranavananda in the 1930s, who based on the tradition of local Tibetans, or on the Kobei glacier, as determined by Swedish explorer Sven Hedin in 1907.
The river is 3,848 kilometers long, and its drainage area is 712,035 square kilometers, according to the new findings, while previous documents showed its length varied from 2,900 to 3,350 kilometers, and its drainage area between 520,000 and 1.73 million square kilometers.
Liu's team found that the Indus River, which provides invaluable agricultural irrigation for Pakistan, originates in a valley northeast of Kailash, the highest peak of the Gangdise Mountain, in Geji County of Tibet.
Its headstream, called Banggokong by local Tibetans, is about 30 kilometers away from Senge Khambab, which Sven Hedin believed was the source of the river more than 100 years ago, said Liu.
The new findings show that the Indus River is 3,600 kilometers long, against previously believed 2,900 or 3,200 kilometers. Its drainage area is more than one million square kilometers, according to Liu's research.
The river runs through China, India and Pakistan, with nearly 200 million people living in its drainage basin.
The Salween River, known to the Chinese as Nujiang, was found to originate from the Jammergangarlor glacier located on the southern side of the Tanggula Mountain in Amdo County of Tibet.
The length of the river is 3,562 kilometers, and its drainage area is 266,037 square kilometers, according to the new findings.
Liu said that only vague descriptions regarding the source of the river were available before his team completed their research.
The Irrawaddy River, one of the most important commercial waterways in Myanmar, was found to originate from the Laka Co on the southern side of the Baxoila Range in Zayu County of Tibet.
The new findings show the river is 2,288 kilometers long, and its drainage area is 420,934 square kilometers. In previous documents, the river's length was recorded between 1,600 and 2,720 kilometers.
The headstreams of Brahmaputra, Indus and Salween perch above an altitude of more than 5,300 meters, while that of Irrawaddy stands at more than 4,700 meters, according to Liu's findings.