Study On Streamflow Variation Of Gulang River Recorded By Tree-ring In The Southeastern Margin Of The Tengger Desert

With the global warming,the water cycle process changes to some extent.The Tengger Desert is located in the northwestern inland of China,with a dry climate and is more sensitive to the change of water cycle in this area.Gulang River originated from the eastern of Qilian,and is located in the southeastern margin of the Tengger Desert.Gulang River is an important part of Shiyang River Basin,and it also is a typical inland river.The change of river hydrological elements will not only affect the ecosystem security of the region,but also affect the regional sustainable development of society and economy,and it may also have a profound impact on the ecological security and production and life of other nearby areas.Therefore,to understand the regional hydrological and climate change and master hydrological and water resources change will play an important role in promoting the rational development and utilization of water resources in this region and maintaining the ecological security of the region and even the Northwest region.In this paper,we established residual chronology table and analyzed the relationship between tree growth and streamflow of Gulang River based on the tree ring data of Pinus tabulaeformis(Carr.)from the Changling Mountain located in the southeastern margin of the Tengger Desert in Gansu Province.Then we reconstructed the historical change of Gulang River in the southeastern margin of the Tengger Desert,and summarized the characteristics of streamflow variation.The main research contents and conclusions of this paper were as follows:(1)Standard chronology and the residual chronology of Pinus tabulaeformis were established after standardization of laboratory samples.The statistical characteristics of the chronology indicate that the residual chronology contained strong public signal and reached a high level than the standard chronology,and its means sensitivity,correlation between samples,signal to noise ratio,expressed population signal and the variance in the first principal component were higher than those of the standard chronology,which meant the residual chronology was superior to the standard chronology.The quality of the residual chronology was higher,which could be used for reconstruction.(2)The climate factors are an intermediate factor between tree growth and hydrological factors.It was found that precipitation from March to May during the growing season was obviously positively correlated with tree growth,and temperature(September of the previous year)in late growing season of the previous year was negatively correlated with tree growth.Streamflow was significantly positively correlated with precipitation from March to August,and it also was negatively correlated with temperature from June to October.It was concluded that there was a correlation between the tree growth and river streamflow.The correlation analysis between the residual chronology of Pinus tabulaeformis and the streamflow of Gulang River showed that the tree ring chronology was significantly positively correlated with the Gulang River from May to July,and the correlation coefficient was 0.713 and reached the significant level of 0.01.Therefore,by using the tree ring chronology of Pinus tabulaeformis to reconstruct the streamflow changes of Gulang River from May to July.(3)The reconstruction model explained 50.9% of the variation of Gulang River streamflow,and adjusted variance was 49%,proving that the reconstruction model was stable and reliable.Moreover,the reconstructed sequence was in good agreement with the observed sequence,which further proved that the transformation equation was reliable.(4)The streamflow of Gulang River from May to July over the past 158 years has experienced three times high flow periods,four times low flow periods and twelve times normal flow periods.The longest high flow periods,low flow periods and normal flow periods were 6 years,9 years and 22 years.The high-and the low flow periods coincided with the flood-and drought years in historical records,respectively.(5)37 years of the extremely-high streamflow occurred over the past 158 a in the reconstruction model,accounting for 23% of the total length of years.The percentage of above-average streamflow years was 3% than the below-average streamflow years.The extremely-high-and above-average streamflow years together appeared 68 times which accounted for 43% of the total years.The extremely-low-and below-average streamflow years together appeared 62 times which accounted for 39% of the total years.These above results indicated that the change of streamflow of Gulang River was unstable greatly from May to July over the past 158 years.(6)There existed clear periods of 110 a,60a,11 a and 4?5a in the streamflow of Gulang River,which was consistent with the ENSO and solar activity.This meant that the Gulang River had a certain degree of response to climate change at a lager global scale.