Tree Ring Width Based Winter Temperature Reconstruction And Its Variation Over The Past Nearly Three Hundred Years In Southwestern Sichuan Province

The Western Sichuan Plateau is located in the eastern part of the Tibetan Plateau,which is the transition area from the Tibetan Plateau to the second class in China.Its climate change has obvious characteristics of the transition zone,and it is an ideal area to study the past climate change.Tree ring has become one of the important indicators of climate change in the past because of its accurate dating,strong continuity,high resolution,easy access and large number of copies.Because of its special geographical location and rich forest resources,the research on tree ring climate reconstruction is relatively early in Western Sichuan Plateau.However,most of the research on tree ring is concentrated in the central and northern part of Western Sichuan Plateau,while the research on tree ring in the southern part of Western Sichuan Plateau is relatively less.Based on the tree ring data of two sampling sites of Abies georgei in Luoji Mountain Area of Western Sichuan Plateau,two tree ring width standard chronologies and residual chronologies were established.Through correlation analysis,it is found that the chronology has strong commonality and the correlation coefficient reaches the 99% confidence level.Therefore,the tree ring data of two sampling points are mixed and processed,and a synthetic tree ring width chronology is established to represent the growth and change of regional trees,and its characteristics are analyzed.The results are as follows:(1)The tree ring-width chronologies of Abies georgei contain more climate and environmental information.The statistical parameters in the chronologies are higher,and the signal-to-noise ratio(SNR)and sample population explanatory power(EPS)are more than 10 and 0.9,respectively.The statistical parameters of the synthetic tree ring width chronology are higher than those of single tree ring width chronology.(2)The results of correlation analysis showed that the tree ring width standard chronology and residual chronology of Abies georgei were significant correlation with the monthly average temperature(mean temperature,mean maximum temperature and mean minimum temperature)from March of the previous year to November of the current year in Yanyuan meteorological station,but had a poor correlation with the monthly precipitation and monthly average relative humidity.The standard chronology of Abies georgei has the best correlation with the mean minimum temperature.In order to find the best reconstruction month,the standard chronology and the residual chronology of Abies georgei tree ring width were correlated with the climate factors in different periods of Yanyuan station.The results showed that the standard chronology of Abies georgei has a good correlation with the mean minimum temperature from November of the previous year to march of the current year(p11-c3),and the correlation coefficient is more than 0.6(p < 0.01).Therefore,the mean minimum temperature of winter half-year(p11-c3)in this area was selected for reconstruction.(3)Based on the linear regression equation,the mean minimum temperature(p11-c3)in the winter half-year of 1730-2014 in southwest Sichuan was reconstructed.The mean minimum temperature reconstruction sequence experienced six warmer periods(1737-1748,1764-1786,1798-1802,1827-1883,1899-1909 and 1988-2014)and six cooler periods(1730-1736,1749-1763,1787-1797,1803-1826,1884-1898 and 1910-1987).(4)Multi window spectral analysis(MTM)was used to detect the periodic signal of the the mean minimum temperature reconstructed sequence in winter half year.The results showed that sequence had periodic changes of 2.3-2.4 years(p < 0.01),3.9 years(p < 0.05),4.6 years(p < 0.1),8.1-8.3 years(p <0.1),9-9.4 years(p < 0.01),9.8 years(p < 0.05),13.8-15.4 years(p < 0.1),23-28.2 years(p < 0.05),57.4years(p < 0.1)and 116.5 years(p < 0.1).Wavelet analysis also found 4-years,10-years,13.8-15.4years and 23-28.2 years periods,which may be related to the El Nino/Southern Oscillation(ENSO),solar activity and the Pacific Decadal Oscillation(PDO).While the period of 57.4 years may be related to the Atlantic Multidecadal Oscillation(AMO),but the specific factors needs to be further explored.(5)The results of spatial analysis show that the reconstruction sequence of the mean minimum temperature in winter half-year can well represent the regional climate change in the Tibetan Plateau and most parts of North China.In addition,the reconstruction sequence is compared with other reconstruction sequence and historical literature around in the surrounding area of the study area,and it is found that these reconstructed sequences have good consistency,which indicates that the reconstructed sequences in this study are reliable.There are relatively few researches on tree ring climate in the southern part of Western Sichuan Plateau,and there may be some uncertain factors from point to area.We hope to have the opportunity to continue to work in this area in the future,arrange more sampling points,and then conduct in-depth study on area reconstruction,so as to more accurately analyze the impact of global climate change on tree growth.