Comparison Analysis of Runoff Change in the Source Regions of the Yangtze and Yellow Rivers

Climate and water environment is different between the source regions of the Yangtze River and that of Yellow River. Climate in the source regions of the Yangtze River is colder, with mean annual temperature below 0 ℃ in the most of the regions. But mean annual temperature of the source regions of the Yellow River is higher than 0 ℃. Precipitation is less in the source regions of the Yangtze River, ranging from 250 to 480 mm, while precipitation ranges from 300 to 760 mm in the source regions of the Yellow River. So the surface runoffs in the two hydrological systems have some difference in distribution within a year and multi-annual variation. By analyzing runoff variations within a year and multi-annual variation in the source regions of the Yangtze and Yellow Rivers, it is found that the surface runoff in the source regions of the Yellow River has uniformity distribution feature in comparison with that in the source of the Yangtze River. It is identified that there were 21 low water years and 19 rich water years in the period from 1961 to 2000 in the source regions of the Yangtze River. But in the source regions of the Yellow River there were 27 low water years and 17 rich water years from 1956 to 1999. In the recent 40 years, the runoff evolution in the source regions of the Yangtze River experiences a process of wet-dry-wet-dry. However in the source regions of the Yellow River it is a process of dry-wet-dry. Mean annual runoff in the source regions of the Yangtze River has a period of 8～9 a obviously. But in the source regions of the Yellow River the period is 7～8 a. The factors, such as precipitation and temperature, which influence runoff mainly, are analyzed by multiple regressions. It is found that temperature is more active in the source regions of the Yangtze River and precipitation is more prominent in the source regions of the Yellow River. Water environment in the cold regions is more important in the source regions of the Yangtze River rather than in the source regions of the Yellow River. It is the leading cause why there is different in runoff between the source regions of the Yangtze River and the Yellow River.