The huge mountains on the Qinghai-Tibet Plateau have bred modern glaciers. Melted ice becomes the source of many well known rivers in Asia. In Tibet there are more than 20 rivers each with a drainage area of more than 10,000 square km, and over 100 each with a drainage area of more than 2,000 square km. The region has rivers known in the world including the Yarlung Zangbo River and its five tributaries such as the Lhasa Nyang Qu, Nyang, Parlung Zangbo and Dorxung Zangbo. It many tributaries on the upper reaches of the Yangtze river and the Lancanjiang (its lower reaches called Mekong River).

  Some of the rivers in Tibet flow into the sea while the others are just inland waters. The average annual runoff stands at 448.2 billion cubic meters. Most of the rivers that ultimately empty into the Pacific Ocean or the Indian Ocean are distributed in the border areas of east, south and west Tibet. The inland rivers are mainly distributed on the Northern Tibetan Plateau. Snows on high mountains are headwaters of these rivers, which are usually short and developed surrounding an endorheic lake. Most of them are seasonal waters. Their lower reches either disappear in the wildness or accumulated into a lake at lower land.

  Yarlung Zangbo. Seens as “Mother River” by Tibetans, it is the largest river in the Tibet Autonomous Region. Originating in the Gyima Yangzong Glacier (5,500 meters above sea level) in Zhongba County at the northern foot of the Himalayas, it runs through 23 counties of Xigaze, Lhasa, Shannan and Nyingchi. After leaving Medog County, it becomes Brahmaputra River which empties into the Indian Ocean when passing through India and Bangladesh. The Yarlung Zangbo River runs 2,057 km in China (ranking fifth in China in terms of length), draining an area of 240,000 square km (sixth in China). With the drainage area having an average elevation of 4,500 meters, the Yarlung Zangbo is the highest river in the world. About 1 million people, or 37 percent of Tibet’s total population, live in the area drained by the Yarlung Zangbo River, where cultivated land amounts to over 150,000 hectares, or 41.67 percent of the region’s total. The area is also home to some major cities and towns, including Lhasa, Xigaze, Gyangze, Zetang and Bayi.

  Yarlung Zangbo Grand Canyon. The Yarlung Zangbo River cleaves a straight niche from west to east before reching the juncture of Mainling and Medog counties, where it swerves around towering Najagbarwa (7,782 meters), the highest peak in the eastern section of the Himalayas, creating the largest, U-shaped canyon in the world. In 19441, some Chinese scientists made an expedition trip along the canyon. Data published by the State Bureau of Surveying and Mapping following the expedition shows that the canyon starts from the Daduka Village, Mainling County in the north and ends at Parcoka Village, Medog in the south. Stretching 504.6 km, the canyon is 2,268 meters deep on average, with the deepest point being 6,009 meters. The Colorado Canyon in the United States is 440 km in length while the Colca Canyon in Peru is 3,203 meters deep. In September 1998, the State Council officially approved the name of the canyon as “Yarlung Zangbo Daxiagu” (Yarlung Zangbo Grand Canyon).

( Source: China's Tibet Facts & Figures 2008)