Tree-ring Based Climate And Streamflow Reconstructions During Historical Period For The Upstream Of The Shiyang River

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 hydrologic observation data were short and clearly insufficient for understanding the extremes, and how hydrological variability may be changing in a warming world. And few high-resolution and long researches had been carried out in this region yet. Compared with most of palaeoclimatological proxies, tree-ring showed advantages in its relative high-resolution and annual time-series for calibrating the relationships between climate and proxy, and it had been well established as records of past climate and streaflow changes. The upstream of the Shiyang River was chosen as the focuses of this study. We present some of the first hydrometeorological reconstructions for this region using a tree-ring chronology network from Picea crassifolia using multiple sites across Lenglongling Mountain, and extended available instrumental observations by more than one century. The results should contribute to sustainable water management solutions in the face of increasing water scarcity and growing conflicts over water use for the Shiyang River Basin and to the methodology of incorporating tree-ring data in the assessment of the probability of hydrologic drought.Twenty-one sampling sites were selected in the upstream of the Shiyang River, and a total of 805 increment cores were extracted with standard increment borers. Cores were cross-dated by visual growth pattern matching, statistical tests in the software package TSAP and skeleton in the WinDENDRO, possible dating errors were re-checked using the quality control software COFECHA. Finally, thirty-four new tree-ring width chronologies, four maximum density chronologies, thirty-four minimum gray chronologies, and twelve maximum gray chronologies were developed in study area.Width chronologies were significant related to precipitation from previous September to current April, mean temperature from January to August, and mean PDSI (Palmer Drought Severity Index) from previous September to current August. Correlation and stability analyses calculated by the program of DendroClim2002 showed that regional moisture conditions were the main environmental factor limiting tree growth at Lenglongling Mountain and PDSI as a predictand for drought reconstructions was much more appropriate than any climatic variable. Two maximum density standardized chronologies were significant negative related to maximum temperature from January to August, minimum gray chronologies were significant positive related to maximum temperature from January to August, and maximum gray chronologies were negative related to summer temperature.Drought fluctuations in the upstream of the Shiyang River were reconstructed using nest and linear regressions. PDSI reconstructions successfully captured both high-frequency (three extreme drought events and two significant humid events) and low-frequency (three obvious descendent periods and two ascendant periods) variations of local moisture availability. By comparing our reconstruction with other available drought reconstructions, the results indicated that good consistency in multi-decadal-scale moisture variations in Qilian Mountains and similar regional moisture variations and analogous modes of climate forcing on tree growth in the northwest margin of the Asian monsoon. Mean maximum temperature from January to August in the upstream of the Shiyang River was reconstructed based on minimum gray chronologies. During 1920s,1930s,1960s and 1990s, the climate was warm and dry. The dominant periodicities of drought and temperature reconstructions were 35,4.14 and 2.6-years obtained by multi-taper method of spectrum analysis. Climate change in study area was closely related to surface sea temperature variations in Pacific.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 chronologies were significantly and strongly related to total runoff from September of the previous year to August of the growing year (RSA), 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. Therefore, precipitation played a role of bridge and tie between tree-rings and runoff. Then, annual runoff series of Jinta, Zamu and Huangyang Rivers were reconstructed according to multiple linear stepwise regression models, and runoff series of Xiying River were reconstructed utilizing principal components extraction and stepwise regression, and all models were tested by the methods of leave-one-out and cross-verification. There was a notable correlation between four runoff series, with a correlation coefficient of 0.52. Four series had the same change tendency, 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). The dominant periods calculated by MTM spectrum analysis were 2-4 and 35 years at different significant levels.