Lai Zuming
In the recent thirty or fourty years, climate warming is distinct in West China due to rapidly developing of industries and agriculture, increasing the greenhouse gases in atomosphere. Statistics of the data of 77 meteorological stations show that air temperature in West China had risen 0.3℃ on the average in the 1980′s as compared to that in the 1950′s.The temperature increase rate during the 30 years greatly exceeds the rate of 0.5℃/100a for the global scale and the rate of 0.17℃/30a for the whole China. In the recent years, temperature rising is always accompanied by precipitation decreasing. Therefore since the 1970′s the main tendency of runoff variation is clearly decreasing in northwestern China and the tibetan Plateau. Form the late 1950′s to the 1980′s the tolal runoff reduced 6.4% in Xinjiang Region, and from the 1960′s to the 1980′s it reduced 13.2% onthe average in the three large rivers in southeastern Tibet Region. They are the Yarlung Zangbo River, the Nujiang River and the Lanchang River. The decreasing range in Xinjiang Region is less than that in southeastern Tibet Region. The reason is that precipitation decreasing is compensated by glacier and snow meltwater increasing in Xinjiang Region. In southeast tibet Region, though there are manyglaciers, even the glacierized area larger than that in the inland basins in Xinjiang Region, more plentiful precipitation becomes the main factor governing the variation in runoff, surpassing the meltwater. Prediction by a statistics model show that in the future 25 years the total runoff in northwestern China will decrease about 4%, but the average runoff of the large rivers (Yarlung Zangbo River, Nujiang River, Lancang River, Jinsha River, Yalong Riverand Dadu River)in the southeastern Tibetan Plateau will increase about 6% as compared with the runoff in the recent 34 years.
