Runoff variations at the source of the Yangtze River over the past 639 years based on tree-ring data

Tree-ring width data collected at five sites near the source of the Yangtze River were used to construct a comprehensive regional chronology. The tree-ring widths exhibited a significant positive correlation with the runoff in the source area of the Yangtze River in multiple months. The most significant correlation was with annual runoff (previous September to the current August), the correlation coefficient was 0.665 (n = 56,p < 0.0001). A record of the annual runoff of the Yangtze River at its source from 1374 to 2012 was then reconstructed. The reconstruction equation was stable and explained 44.2 % of the variance (adjusted R-2 = 43.2%, n = 56, F = 42.86). The reconstruction indicated that 17 periods of high flow and 14 periods of low flow have occurred over the past 639 yr. The longest periods of high flow occurred during 1615-1643 and 1755-1783, while the longest period of low flow occurred during 1445-1490. The wet and dry periods in the reconstruction coincided with similar periods identified in a time series of Palmer drought severity index values obtained near the research area, and a time series of reconstructed streamflow in the upper Yellow River. Several important periods of low flow also coincided with periods of drought that affected broader regions. An analysis using the multi-taper method demonstrated that periodic variations in runoff of 2-5 yr, ca. 20 yr, and ca. 50 yr have occurred at the source of the Yangtze River. Furthermore, the relationships between annual runoff and solar activity and the intensity of the southwest Asian summer monsoon (also known as the Indian monsoon) are discussed in this article.