Abstract:

This study employs a nested principal component regression model to reconstruct the natural annual runoff series for the Yangtze River source region from 1433 to 2002. It explores historical variability, the evolution of wet and dry events, and periodic fluctuations. Using tree-ring data and observed runoff data, the model’s accuracy is validated through evaluation indicators (CRSQ, VRSQ, RE, and CE). Results indicate that over the past 570 years, the annual runoff in the Yangtze River source region has experienced significant fluctuations. Six wet periods and nine dry periods are identified, with the longest wet periods occurring from 1451 to 1510 and from 1596 to 1645, and the longest dry period spanning from 1848 to 1903. The dry periods during the reconstruction period align with droughts on the Tibetan Plateau and in other areas of the Yangtze River basin, suggesting that the reconstructed runoff changes in the Yangtze River source region reflect large-scale climate fluctuations. Furthermore, the reconstructed runoff series for the Yangtze River source region exhibits significant periodic fluctuations at intervals of 4-8 years, 16-32 years, 50-100 years, and 100-200 years. These fluctuations are likely driven by the combined effects of ENSO (El Niño-Southern Oscillation), the East Asian Summer Monsoon (EASM), the Pacific Decadal Oscillation (PDO), and the Atlantic Multidecadal Oscillation (AMO), and also reflect the impact of global climate change and the trends of glacier and snowmelt on the Tibetan Plateau.

Key words: runoff, reconstruction, tree annual rings, nested principal component regression model, Yangtze River source region