Study On Temperature And Humidity Changes During The Past 300 Years In Tianshan Mountains Region Of China In The Past 300years Based On The Tree-ring Records

Climate change in the form of widespread global warming has been a major concern of researchers for decades.Tianshan Mountains,located in the northwest of China,is an important part of the arid and semi-arid regions,known as the "wet island" of the arid region.The special geographical location and environment make the region's response to global climate change very obvious.The spatial variation of temperature and precipitation caused by climate change leads to many uncertainties in the use of effectively available water resources in arid areas.This makes it difficult for the northwest economic construction which is closely related to water resources to develop orderly.Therefore,it is necessary to clarify the law and internal mechanism of climate change in this region.However,the limited meteorological data limit the study of regional climate change characteristics and trends,must find suitable climatic proxy data,and tree rings have the advantages of accurate dating,high resolution,wide sample distribution and so on,and in such aspects as historical climate reconstruction and paleoenvironment evolution has been well applied.This study analyzed and discussed the changes of the temperature and humidity in the western and middle-eastern of Tianshan Mountains over the past hundred years according to the water gradient based on the data of the width of the tree rings in Tianshan Mountains.Firstly,the relationship between the radial growth of trees in the two regions and the climate response was analyzed with the data of the width of tree rings in the western and middle-eastern of Tianshan Mountains respectively,and the main climate factor of the radial growth of trees recorded by the tree rings were identified.Secondly,the moving correlation method is used to test the time response stability between the tree rings width chronology and the main climate factor.Finally,the history of the mean minimum temperature variation in the western part of Tianshan Mountain and the history of the dry and wet variation in the middle-eastern of Tianshan Mountains are reconstructed respectively.The main conclusions are as follows:(1)According to the statistics and analysis of the width chronology and its parameters,the values of mean sensitivity(MS),expressed population signal(EPS),first-order autocorrelation coefficient(AC1)and signal-to-noise ratio(SNR)are relatively high,which all meet the needs of the study of tree-ring climatology,It showsthat the established tree ring width chronology in the western and middle-eastern has high quality and contains more climate signals,which is suitable for the reconstruction of historical climate based on tree rings.Meanwhile,it is found that the chronology of the western and middle-eastern of the Tianshan Mountains has been alternating between high and low values in the past three hundred years after the trend analysis of the chronology width,significant downward trend especially in recent decades.(2)The correlation between the tree ring width chronology of the western Tianshan Mountains and the temperature(weight 59.71%)is obviously better than that of the total precipitation,average evaporation,relative humidity,sunshine hours and station pressure,especially the mean minimum temperature(weight 17.36%)is the main limiting factor for the radial growth of trees in this region.However,the radial growth of trees in the middle-eastern of Tianshan Mountains has the strongest response to the average evaporation(weight 18.99%),and shows a significant negative correlation with temperature and a significant positive correlation with precipitation,indicating that drought is the main climate factor restricting the radial growth of trees.Therefore,response analysis of the drought index-standardized precipitation evapotranspiration index(SPEI)covering multiple indicators in the further,it was found that the drought at the beginning of the growth season(March-May)in the middle and long term(7 months scale)was the main limiting climatic factor in the study area(r=0.704,p<0.01).In the further time stability analysis,the tree ring chronology of both the western and the middle-eastern of Tianshan Mountains has no divergent response to the main restrictive climate factors,which provides a guarantee for the accuracy of the next step of climate reconstruction.(3)The history of the mean minimum temperature from May to September of the previous growing season in the western of Tianshan Mountains and the dry and wet change from March to May in the early part of the growing season in the middle part of282 years was reconstructed by using the regional chronology of the western and middle-eastern of Schrenk spruce(Picea schrenkiana).The results show that both warm years(52%)and extreme warm years(55%)occur more frequently than cold years(48%)and extreme cold years(45%).The frequency of SPEI drought reconstruction series in the middle-eastern was higher in wet(51%)and extreme wet(57%)years.Meanwhile,the distribution of extreme years in each century is also unbalanced.The wet years in the middle and lower 18 th century accounted for a relatively large number,the dry and wet years and the extreme dry and wet years in the 19 th century were basically the same,and the dry and extreme dry years in the 20 th century accounted for a relatively large number.(4)The results of spatial correlation analysis show that the reconstructed series of mean minimum temperature can well represent the variation characteristics of mean minimum temperature in the western of Tianshan Mountains and central Asia.The SPEI reconstructed series can also represent the characteristics of the dry and wet variation in the middle-eastern of Tianshan Mountains and the surrounding area.The spatial correlation with SST and the multi-window spectral periodic analysis reveal that the variation of the mean minimum temperature in the western of Tianshan Mountains is mainly influenced by the interaction of solar activity,large-scale sea-air change and westerly circulation.However,the middle-eastern of the dry and wet changes of the multi-window spectrum period analysis indicate that the dry-wet variation in the middle-eastern of Tianshan Mountains is mainly affected by the westerly circulation represented by the north Atlantic oscillation index(NAO).