Qinghai Lake, the largest closed interior saline lake in China with a basin area of 29661km² and an altitude of about 3000m, is located in the northeast of the Q inghai-Xizang Pleateau, Being a long distance from the industrial region and affected by less human activities, it is actually in a semi-natural condition.Hence the lake is a place favorable for investigation of the environmental and climatic changes.As shown by the calculated results of water balance and the measured data during the recent 30 years (1959-1988), the water balance of Qinghai Lake was in a negative situation.The lake has decreased 2.96m in water level during the past 30 years, about 1 0.2cm per year.If the climatic scenarios of Qinghai Lake continues, the lake will have its level dropped 5.8m in 57 years later (2045).When considering "Green House Effect" and its impacts on climatic scenarios,it is estimated that the lake level will be continually descending at a speed of 10.1cm per year.