Streamflow variations of the Yellow River over the past 593 years in western China reconstructed from tree rings

Annual streamflow of the Yellow River has decreased in recent years ( 1980 to 2000) because of climate change and human activity. This decrease affects the environment and the lives of the people in the drainage area. Tree ring width chronologies from six sites in the headwaters of the Yellow River were developed to provide estimates of past Yellow River streamflow in order to place the recent flow reduction in a long-term context. The ring width indices of the six local Juniperus przewalski chronologies correlate significantly with the observed streamflow of the Yellow River recorded at the Tangnaihai hydrological station. Principal components analysis shows that the first principal component ( PC) of the tree ring indices explains 49% of the streamflow variance. On the basis of this result, Yellow River streamflow was reconstructed for the past 593 years. Several severe droughts and low-flow events are recognized in the decades 1920-1930, 1820-1830, 1700-1710, 1590-1600, and 1480-1490. The most severe droughts in 1480-1490 were also recorded in other studies on the Tibetan Plateau. Regional historical climate archives further support the validity of our streamflow reconstruction. The reconstructed increase in streamflow during much of the twentieth century also coincides with generally wetter conditions in the Tienshan and Qilianshan Mountains of China, as well as in northern Pakistan and Mongolia. After the 1980s, our reconstruction indicates a decreasing trend in streamflow, which is cause for concern. Presently, Yellow River streamflow is relatively low but not yet outside the range of streamflow fluctuations that occurred during the past six centuries.