Study On The Response Of Tree-ring Stable Oxygen Isotopes And Hydrological Factors In Dongda Mountains Of Hexi Corridor

The Hexi Corridor is one of the most important agricultural areas in Northwest China,the main artery of the"Silk Road",and an essential area for the implementation of China's"the Belt and Road"development strategy.Due to global climate change,The environment and hydrological processes in the Hexi Corridor are undergoing significant changes,and the frequency of extreme weather events is increasing.Dongda Mountains is located in the Hexi Corridor.It is great significance to understand the history of climate evolution in the region to increase the knowledge of the current climate situation and predict the impact of future climate evolution on human production and life.In this paper,the response of stable oxygen isotope changes in tree ring to climate on a regional scale was investigated by using Picea crassifolia tree ring samples taken from Dongda Mountains,and the possible connection between regional water vapor sources and their relationship with the global large-scale climate system was explored.The main conclusions are as follows:(1)The cellulose was extracted from the tree ring samples collected from Dongda Mountains in Hexi Corridor and its?¹⁸O value was determined.The chronology series of tree ring?¹⁸O from 1807-2011 was established.There are similar trends between the tree ring oxygen isotopes and the atmospheric precipitation?¹⁸O from Chengdu,Baotou,and Taiyuan stations,and the tree ring?¹⁸O reflects similar monsoonal precipitation forms.Based on the calculation results of the correlation analysis,the linear regression equation was used to reconstruct the average water vapor pressure changes in the Dongda Mountains area from July to August in the past 205 years.(2)There were 29 wet years(14.1%of the full series)and 30 dry years(14.6%of the full series)in the reconstructed series in the past 205 years.After 10-years low pass filtering of the reconstructed series,six wetter periods and seven drier periods were found.At the beginning of the 20th century,there was a continuous dry trend,and after 2000,the degree of drought intensified.(3)The dry and wet changes of water vapor pressure in the Dongda Mountains area mostly corresponded well to the drought and flood years in the historical change period.The reconstructed July-August mean water vapor pressure series is very consistent with the sc PDSI series and DWI series changes in the Hexi area.They can jointly reflect the historical dry and wet change process in the region,verifying the accuracy of the reconstructed series.(4)EEMD analysis found that the reconstructed sequence has periodic changes of 2.87a,6.37a,13.6a,25.5a,and 68a;while wavelet analysis found that there are periodic changes of2-4a,5-7a,10-14a,and 16-25a.The results obtained by the two period analysis methods are quite consistent.The period analysis results indicate that the ENSO phenomenon and solar activity may influence the climate change in the Hexi Corridor area.(5)Combining the Asian monsoon index,the tree ring data of the monsoon zone and mid-latitude Asian westerly zone,and the analysis of modern observation data,it is found that the Dongda Mountains area is affected by the Asian monsoon and the westerly circulation at the same time.The water vapor pressure reconstruction series has a certain spatial correlation with the Nino3.4 region SST,and has a significant correlation with the Nino3.4 index series(r=-0.273).ENSO affects the moisture change condition in the region by affecting the intensity of Asian summer monsoon.Water vapor pressure changes are also influenced by solar activity,when the solar activity is stronger,the climate in the area is drier.The reconstruction results in this paper provide a basis for understanding past dry and wet changes in the study area.However,the length of the reconstructed water vapor pressure series is limited,and the tree ring samples are only from 1 sampling site.Therefore,it is possible to try to establish a longer-scale chronology in this area,combining the tree ring or different indicators chronology of multiple sampling points in the Hexi Corridor area for comprehensive analysis.The driving mechanism behind climate change involved in part of the article needs further analysis.