Abstract:

Runoff at source regions of the Yangtze and Yellow Rivers were derived mostly from precipitation and melt water of glaciers, snow and frozen earth. Changes of the temperature and its impact on the ablation of the glaciers and snow influenced directly the runoff. In this paper, the authors analyzed how the runoff changes responded to the fluctuation of temperature and precipitation by means of crossspectral analysis. By crossamplitude function (CAF) and the simpledensity spectrum, some new functions such as coherence function, gain function and phase spectrum function were calculated. It was indicated that the runoff fluctuation was influenced much more by precipitation, and being more obvious in the source region of the Yellow River than in the source of the Yangtze River. However, temperature influenced slightly the fluctuation of the runoff, not comparable with the major effect of precipitation at the source region of the Yellow River and also at the source of the Yangtze River. Runoff at source regions of the Yangtze and Yellow Rivers has decreased since late 1980's, which had some negative effects on water resource in lakes, swamp and frozen earth, and then the whole environment.

Key words: runoff, fluctuations, cross spectral analysis, source regions of the Yangtze and Yellow Rivers