Abstract: The distributive pattern of the alpine ecosystem in the source regions of the Yangtze River and Yellow River was analyzed based on the aerial photo in 1967 and the TM remote sensing data obtained in 1986 and 2000; the relationship of changes in the alpine ecosystem with climate was then analyzed based on the climatic observation data; and the effect of changes in the land surface terrestrial ecological system on the hydrological process of the river source region was analyzed using runoff coefficient, rainfall-runoff relationship, flow duration curve, and water conservation index etc. Results show that the alpine ecosystem persistently degraded over the last 40 years, the area of high coverage alpine meadow and alpine steppe decreased, while wetland shrunk and desertified meadow increased. The permafrost thawing due to temperature rise is one of the main factors which led to the degradation of the alpine ecosystem. The changing of temperature was significantly negatively correlated with the areas of high coverage alpine meadow, alpine steppe and alpine swamp meadow. The degradation of land surface terrestrial ecosystem has significantly affected the hydrological process in the source regions; under the condition that precipitation changed slightly, the relation between the persistent decline of runoff coefficient and precipitation-runoff attenuated, the frequency of flood increased, and the outflow and water conservation index persistently decreased. It is urgent to pay much attention to cope with the climatic change and to sustain the alpine ecosystem's function in the source regions.

Key words: river source region, Yangtze River, Yellow River, alpine ecosystem, climatic change, hydrologic effect