As a consequence of global warming and an enhanced water cycle, the climate changed in northwest China, most notably in the Xinjiang area in the year 1987. Precipitation, glacial melt water and river runoff and air temperature increased continuously during the last decades, as did also the water level of inland lakes and the frequency of flood disasters. As a result, the vegetation cover is improved, number of days with sand-dust storms reduced. From the end of the 19th century to the 1970s, the climate was warm and dry, and then changed to warm and wet. The effects on northwest China can be classified into three classes by using the relation between precipitation and evaporation increase. If precipitation increases more than evaporation, runoff increases and lake water levels rise. We identify regions with: (1) notable change, (2) slight change and (3) no change. The future climate for doubled CO 2 concentration is simulated in a nested approach with the regional climate model-RegCM2. The annual temperature will increase by 2.7 • C and annual precipitation by 25%. The cooling effect of aerosols and natural factors will reduce this increase to 2.0 • C and 19% of precipitation. As a consequence, annual runoff may increase by more than 10%.

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