Runoff Changes and Distributed Hydrologic Simulation in the Upper Reaches of Yangtze River
长江上游流域径流变化与分布式水文模拟

The Yangtze river from the source regions to the Yichang station is called as the Upper Yangtze River. Its area is about one million square kilometers. The main tributaries of the upper Yangtze River include the Jinsha River, Minjiang River, Tuojiang River, Jialing River and Wujiang River etc. It is desirable to study the variations of runoff at the major stations along the main stream and the major tributaries of the upper Yangtze River basin, and explore the possible causes of the variations. The runoff changes at sixteen main control stations in the upper reaches of Yangtze River basin were analyzed firstly. The results show that except in the Jinsha River basin, the runoff in the other basin decreased more or less. Among them, the runoff in the Minjiang River, Hengjiang River, Tuojiang River, and Jialing River decreased significantly. The runoff at the Cuntan station increased before 1968, and decreased significantly after 1993. According to water resources engineering and hydrologic station distribution, the upper Yangtze River basin was divided into seven areas: 1)Jinsha River basin; 2)Minjiang River basin; 3) Tuojiang River basin; 4)Jialing River basin; 5)Cuntan area; 6)Wujiang River basin; 7)Yichang area. Then a large scale distributed monthly water balance model was developed and applied in the above seven areas. In the calibration period, the average value of Nash-Sutcliffe efficiency is 85.00% and that in the verification period is 81.69%. So the model can simulate monthly runoff well in the upper Yangtze River basin. Finally, the model was used to evaluate the impacts of climate change and human activities on the changes of runoff generation in the upper Yangtze River basin. Using the fixing-changing factor technique, the contribution rates of climate change and human activities on runoff change were evaluated. The runoff at the Cuntan station of Yangtze River decreased significantly since 1993 and climate change is the main factor that the contribution rate of which was 71.43%. But in the non-flood period the reservoirs operation in the upper Yangtze River basin increased runoff somewhat. Meanwhile, it need to be paid attention to that the runoff in the Minjiang and Jialing River basin decreased obviously and the contribution of human activities to runoff change reaches to about a half. Human activities have most probably played a dominant role in influencing the discharge of the Minjiang and Jialing River basin.