Latewood width(LWW)indices of trees are considered a reliable proxy of summer precipitation in the Northern Hemisphere.However,the strong coupling and high correlation between earlywood width(EWW)and LWW indices often...Latewood width(LWW)indices of trees are considered a reliable proxy of summer precipitation in the Northern Hemisphere.However,the strong coupling and high correlation between earlywood width(EWW)and LWW indices often prevent registration of climate signals of the LWW index.In this study,328-year-long earlywood width and latewood width chronologies were developed from Chinese pine at two sites in the Hasi Mountains,north central China.The climate responses of these chronologies were analyzed and the LWW index used to derive sum-mer precipitation signals.Correlation analyses showed that LWW was particularly influenced by earlywood growth and recorded stronger climate signals of the previous year as EWW,rather than those of the current year with infrequent summer climate signals.However,after removing the effect of earlywood growth using a simple regression model,the adjusted LWW chronology(LWW_(adj))showed a strong relationship with July precipitation in dry years.This suggests that the LWW_(adj) chronology has the potential to be used to investigate long-term variability in summer precipitation in drought-limited regions.展开更多
Our understanding of the long-term hydroclimate variations in South China is prohibited by the shortness of me- teorological records. Paleoclimatic proxies, such as tree-rings, can be pursued to extend the meteorologi...Our understanding of the long-term hydroclimate variations in South China is prohibited by the shortness of me- teorological records. Paleoclimatic proxies, such as tree-rings, can be pursued to extend the meteorological records back for centuries to help us better understand hydroclimatic conditions. In this study, we reconstructed the July--Au- gust standardized precipitafio^evapotranspiration index （SPEIjut Aug） based on a newly developed 127-yr adjusted latewood width chronology from Tsuga longibracteata, South China. The chronology explained 40% of the actual SPEIjul Aug variance in the period 1953-2014. The reconstructed SPEIjuI Aug can represent large-scale July-August SPEI variations over South China, including northern Guangxi, Hunan, and Guizhou provinces. From the perspec- tive of the past 127 years, the extreme summer drought in 2013 was not unusual because more extreme drought events occurred in the first half of the 20th century. A significant 2.0-3.6-yr hydroclimatic cycle existed in the recon- struction, which indicated that the SPEIjulug might be driven by El Nifio-Southern Oscillation （ENSO）. We further checked the time-dependency of the relationship between SPEIJuI_Aug and ENSO and found that it was unstable. Their relationship was weak before the 1950s, became significant from the 1950s to early 1990s, and then dropped to be weak again and even out of phase since the early 1990s, which may be attributable to the significant westward exten- sion of the western Pacific subtropical high.展开更多
In order to investigate the response to climate changes in radial growth of Picea crassifolia at the lower tree line in the middle Qilian mountains in northwestern China, relationships of standardized chronologies of ...In order to investigate the response to climate changes in radial growth of Picea crassifolia at the lower tree line in the middle Qilian mountains in northwestern China, relationships of standardized chronologies of annual ring, earlywood and latewood widths with mean monthly temperature and total monthly precipitation were analyzed by ways of correlation and pointer year analyses. The results show that annual ring, earlywood and latewood widths are significantly negatively correlated with mean monthly temperature in June and July. Annual ring and earlywood widths are significantly and positively correlated with total monthly precipitation in March, May and June and negatively correlated with total monthly precipitation in September. Latewood width is less sensitive to climate changes than the width of earlywood and insignificantly sensitive to precipitation. The results of pointer year analysis revealed that when summer temperatures are higher than the mean summer temperature synchronization and the summer precipitation lower than mean summer precipitation synchronization, narrow annual rings are formed. Wide annual rings are formed when summer temperatures are lower than the mean summer temperature synchronization and summer precipitation higher than mean summer precipitation synchronization. The results indicate that more precipitation in the spring and summer is helpful for radial growth while warmer summer restricts radial growth of P. crassifolia at the lower tree line in the middle Qilian mountains.展开更多
基金supportedbytheNational Natural Science Foundation of China (No.U21A2006 and 42001043).
文摘Latewood width(LWW)indices of trees are considered a reliable proxy of summer precipitation in the Northern Hemisphere.However,the strong coupling and high correlation between earlywood width(EWW)and LWW indices often prevent registration of climate signals of the LWW index.In this study,328-year-long earlywood width and latewood width chronologies were developed from Chinese pine at two sites in the Hasi Mountains,north central China.The climate responses of these chronologies were analyzed and the LWW index used to derive sum-mer precipitation signals.Correlation analyses showed that LWW was particularly influenced by earlywood growth and recorded stronger climate signals of the previous year as EWW,rather than those of the current year with infrequent summer climate signals.However,after removing the effect of earlywood growth using a simple regression model,the adjusted LWW chronology(LWW_(adj))showed a strong relationship with July precipitation in dry years.This suggests that the LWW_(adj) chronology has the potential to be used to investigate long-term variability in summer precipitation in drought-limited regions.
基金Supported by the National Natural Science Foundation of China(41271210)Global Change Program(2016YFA0600503)+1 种基金Priority Academic Program Development of Jiangsu Higher Education InstitutionsJiangsu Collaborative Innovation Center for Climate Change
文摘Our understanding of the long-term hydroclimate variations in South China is prohibited by the shortness of me- teorological records. Paleoclimatic proxies, such as tree-rings, can be pursued to extend the meteorological records back for centuries to help us better understand hydroclimatic conditions. In this study, we reconstructed the July--Au- gust standardized precipitafio^evapotranspiration index （SPEIjut Aug） based on a newly developed 127-yr adjusted latewood width chronology from Tsuga longibracteata, South China. The chronology explained 40% of the actual SPEIjul Aug variance in the period 1953-2014. The reconstructed SPEIjuI Aug can represent large-scale July-August SPEI variations over South China, including northern Guangxi, Hunan, and Guizhou provinces. From the perspec- tive of the past 127 years, the extreme summer drought in 2013 was not unusual because more extreme drought events occurred in the first half of the 20th century. A significant 2.0-3.6-yr hydroclimatic cycle existed in the recon- struction, which indicated that the SPEIjulug might be driven by El Nifio-Southern Oscillation （ENSO）. We further checked the time-dependency of the relationship between SPEIJuI_Aug and ENSO and found that it was unstable. Their relationship was weak before the 1950s, became significant from the 1950s to early 1990s, and then dropped to be weak again and even out of phase since the early 1990s, which may be attributable to the significant westward exten- sion of the western Pacific subtropical high.
基金financially supported by the Special Fund of the National Public Welfare Industry (Forestry) (No.200804001)the National Science Fund for Distinguished Young Scholars (No.30825034)
文摘In order to investigate the response to climate changes in radial growth of Picea crassifolia at the lower tree line in the middle Qilian mountains in northwestern China, relationships of standardized chronologies of annual ring, earlywood and latewood widths with mean monthly temperature and total monthly precipitation were analyzed by ways of correlation and pointer year analyses. The results show that annual ring, earlywood and latewood widths are significantly negatively correlated with mean monthly temperature in June and July. Annual ring and earlywood widths are significantly and positively correlated with total monthly precipitation in March, May and June and negatively correlated with total monthly precipitation in September. Latewood width is less sensitive to climate changes than the width of earlywood and insignificantly sensitive to precipitation. The results of pointer year analysis revealed that when summer temperatures are higher than the mean summer temperature synchronization and the summer precipitation lower than mean summer precipitation synchronization, narrow annual rings are formed. Wide annual rings are formed when summer temperatures are lower than the mean summer temperature synchronization and summer precipitation higher than mean summer precipitation synchronization. The results indicate that more precipitation in the spring and summer is helpful for radial growth while warmer summer restricts radial growth of P. crassifolia at the lower tree line in the middle Qilian mountains.
