中文摘要：

长江-黄河源区属典型寒区，降水、冰雪融水等共同成为径流的补给来源，径流量的变化同时受到区域内降水量和气温变化的影响。采用互谱分析方法研究表明，长江、黄河源区降水与径流周期波动间的关系明显好于气温与径流之间的关系，降水对径流量的主要周期波动有较明显的控制作用。气温虽然对径流量的部分周期波动变化有一定的影响，但不如降水明显。相对来说，黄河源区降水对径流量的波动变化的影响要好于长江源区。20世纪80年代后期长江-黄河源区径流量大幅下降的主要原因是区域内降水量的减少。

英文摘要：

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.