Shule River
The Shule River is a river of the northern Tibetan Plateau and Hexi Corridor of northwestern China. It starts in the Qilian Mountains and flows north then west for about . Historically, the river flowed seasonally into Lop Nur, an intermittent salt lake in the Taklimakan Desert. Due to large irrigation diversions and the gradual desertification of the region, the river dries up about two-thirds of the way along its course in the Kumtag Desert. Course. It rises as glacier melt in a valley on the northern side of the Qilian Mountains or Nan Shan, on the Tibetan  Plateau of extreme northern Qinghai province. In its upper third the river flows generally NNW through deep, glacier-carved valleys and precipitous gorges into Gansu Province, and is known as the Changma. It comes out of the mountains in Guazhou County, and spreads onto a massive inland delta or alluvial fan. Now known as the Shule proper, the river turns due west into an agricultural valley, where most of its water is taken away for irrigation and industrial use. North of Dunhuang, the largest city in the river's basin, it disappears into the desert. The dry river channel stretches  about further WSW to the seasonal Lop Nur basin, which comprises intermittent salt flats, playas and marshes. Watershed. Geography. The Shule's drainage basin covers about of land, with only contributing significant water flow. There are many other valleys and basins that would drain into the river during extreme floods, but because of the aridity of the region, high flow events are rare. The average precipitation in the watershed is per year. In the high mountain areas it can be up to , mostly in the form of snow. In the deserts to the north annual precipitation is usually below and  in some years, no rain falls at all. Most of the Shule's water arises from glaciers. There are 347 glaciers in the upstream catchment area of the river encompassing a total area of . The annual runoff is approximately , ranging from a low of to a high of . Warming temperatures are reducing the size of glaciers feeding the river and may lead to future reductions in water flow. River modifications. The river valley is intensely cultivated and its flow is regulated by two reservoirs, Changma and Shuangta. There are also more than three additional hydropower/diversion dams on the river . The entire flow of the Shule is diverted directly downstream of the mountains into a canal that runs north-northeast across the delta, supplying farms in the valley to the north. This water is eventually returned to the river, but irrigation usage has caused the river to dry up well before its historic terminus. It is surmised that a few thousand years ago, the region was cooler and wetter, and the river had significantly more flow than it does today.