Changes of the water environment in the headwater area of the Yellow River and the cause for the zero-flow of the river occurring in winter

Hydrologic observations of the Yellow River began in1954.Since then zero-flow of the river has occurred three times at the Huangheyan Hydrologic Station in Madoi County.Since1999the zero-flow of the Yellow River has become an issue of extensive concern by the society.On the basis of an analysis of the hydrologic environment of the headwater area of the Yellow River and its influence factors,the authors indicate that due to the low regulation capacities of the thawing areas around the Ngoring Lake and Gyaring Lake,their regulated flow is insufficient to maintain the runoff of the Yellow River during winter or continuous drought seasons and thus the zero-flow occurs.In addition,natural and an-thropogenic factors such as the lowering of the water level of the lake,mining of placer gold and over-grazing also have important influence on the occurrence of the zero-flow of the Yellow River.As the hydraulic power plant built on the river near the outlet of the Ngoring Lake has begun to impound wa-ter,the regulating capabilities of the two lakes and their surrounding areas have increased.Thus the possi-bility of the occurrence of the zero-flow of the river will be reduced considerably in the future.