A Study On The Dry And Wet Changes Based On Tree Ring Width In Northern Shanxi Province

Climate change is closely related to human life.In recent decades,climate change has produced more and more negative impacts on human life,which has also attracted extensive attention from scholars at home and abroad.To better understand future climate change,it is necessary to deeply understand the regularities and characteristics of past climate and environmental changes.With the characteristics of wide distribution,strong continuity,easy availability of samples and high resolution,tree rings have become one of the core proxies in the study of paleocliclimate and paleoenvironment change.The research area of this paper is located in the northern part of Shanxi Province,belonging to the Lüliang Mountains.Climatic characteristics for the semi-arid continental monsoon climate,four distinct seasons.Lüliang Mountain is located near the isoline of 400 mm precipitation in China,which is sensitive to climate change.There are few research results on tree rings climatology in this area,and the water resource shortage in this area is becoming more and more serious in recent years,so it is urgent to construct a comprehensive index series that can reflect the change of climate dry and wet.Palmer drought severity index(PDSI)is a comprehensive climate and environment change index related to precipitation and temperature.It is of scientific value and practical significance to reconstruct long scale PDSI variation sequence based on tree ring data.Based on the existing tree ring width index series,according to the correlation between the standard width chronology of reconstruction and the existing meteorological data(1954-2003),the reconstruction month is determined and the conversion equation is established.The long-scale dry and wet changes sequence in the study area was reconstructed.Based on the above analysis,the following conclusions are drawn:(1)Three chronologies of tree ring width in northern Shanxi in the study area were obtained,named standard chronology(STD),residual chronology(RES)and autoregressive chronology(ARS).The chronology length was 175 years(1829-2003).(2)Correlation analysis and calculation were conducted between the three chronologies and the climate data of Yuanping and Wuzhai meteorological stations near the sampling points.The results showed that the STD chronology was significantly correlated with PDSI data,with the highest correlation being with the average PDSI index between May and June.(3)Based on the correlation analysis results,the linear regression transformation equation was used to reconstruct the change of average PDSI index between May and June in northern Shanxi Province during the past 175 years.The variance interpretation of the transformation equation is 47.16%,46.06% after adjusting the degree of freedom,and the F test value is 42.84.(4)In the reconstructed sequence,the extreme drought years were 4 years in total,accounting for 2.29% of the total sequence;The extremely wet years were 6 years,accounting for 3.43% of the total.After 10 years of low-pass filtering,the reconstructed dry and wet sequence shows 9 wet and 10 dry periods,and the reconstructed sequence shows a trend of increasing drought in the late 20 th century.(5)The results obtained by MTM multi-window spectrum periodic analysis indicate that the climate change in the northwestern mountainous region may be affected by ENSO phenomenon.The calculations related to the East Asian monsoon also indicate that climate change in the study area may be affected by the East Asian monsoon.Other factors affecting climate change in the study area need to be further studied in detail.(6)The reconstructed wet and dry change sequence in the northern part of Shanxi has a better correlation with the DWI sequence generated based on historical literature.The correlation coefficient is-0.235(n=175,P < 0.002).After 10 years of low-pass filtering,the correlation coefficient is-0.404.There are also similarities with other research results in Shanxi Province.Some research results have been achieved in this study,but the length of the reconstructed chronology is limited.In order to study the influence factors of regional climate change at a longer scale,it is necessary to look for older tree ring samples in the study area.At the same time,other tree ring indexes,such as isotopes and densities,can be used to conduct deeply research on paleoclimatology changes in the study area.