HOU Ying, WANG Nai-ang, ZHANG Xue-min, LU Jun-wei
In the past few years, many serious ecological problems caused by the shortage of water resources, such as discontinuous surface runoff, dried lakes, lowered groundwater level, and deteriorated water quality had emerged in the Shiyang River Basin. But the hydrologic observation data were insufficient to understanding the extremes, and how hydrological variability may be changing in a warming world. Few high-resolution and long researches had been carried out in this region yet. Therefore, it’s necessary to sample tree-ring cores, and five new tree-ring width chronologies were developed in the upper reaches of Shiyang River Basin. To understand the hydrologic response of the radial growth of Picea crassifolia, correlation analyses of tree-ring chronologies with precipitation and runoff were conducted. The results showed that five chronologies were significantly and strongly related to total runoff from September of the previous year to August of the growing year (RSA); five chronologies also had significant and positive relationships with total precipitation from September of the previous year to August of the growing year (PSA); and the correlation coefficients between RSA and PSA were significant and positive. So, precipitation played a role of bridge and tie between tree-rings and runoff. Then, annual runoff series of Jinta River were reconstructed according to a multiple linear regression model, and runoff series of Xiying River were reconstructed utilizing principal components extraction and stepwise regression, and two models were tested by the methods of leave-one-out and cross-verification. There was a notable correlation between the two runoff series of Jinta River and Xiying River, with a correlation coefficient of 0.865, and two series had the same change tendency. So, it can be concluded that annual runoff series of Shiyang River had obvious low-frequency and high-frequency variations, and contained four severe dry periods (during 1880-1892, 1925-1935, 1960-1967, and 1997-2002) and three significant wet periods (occurred in 1894-1923, 1935-1959, and 1967-1986), and the appear frequency of low stream years and high stream years tended to middle . The dominant periods calculated by MTM spectrum analysis were 2.58 a, 2.76 a, 3.28 a, 3.53 a, 4.14 a, and 22.2 a at different significant levels.
