基于树木年轮重建大兴安岭北部过去242年4~7月降水量变化

April to July precipitation reconstruction based on tree-ring width for the past 242 years in the northern Greater Khingan Mountains,Northeast China

大兴安岭北部是气候变化的敏感区之一,受限于较短的器测资料,当前对该区域降水量的年际-年代际变化认识仍很薄弱。本研究利用大兴安岭北部满归地区樟子松(Pinus sylvestris var.mongolica)树轮样本,建立树木年轮宽度年表,阐明制约樟子松径向生长的主要气候因子。结果表明:当年春季和生长季前期降水量是满归地区樟子松径向生长的主要限制因子。树木径向生长与当年4~7月降水量(r=0.549,p<0.001)相关性最高。运用一元线性回归模型重建该地区过去242年(1776~2017年,EPS>0.85)以来的当年4~7月降水量,方程方差解释量为30.1%。利用逐一剔除法(leave-one-out)和分段检验法(calibration-verification)对重建方程进行检验,均表明重建序列稳定可靠。过去242年间该地区存在着5个湿润期(1788~1805年、1841~1871年、1887~1899年、1926~1966年和1993~2000年)和6个干旱期(1776~1787年、1806~1840年、1872~1886年、1900~1925年、1967~1992年和2001~2017年),其中1900~1925年是最严重的干旱期。重建降水量的干湿时期与其他序列结果具有较好的一致性,进一步验证了重建结果的可靠性。空间相关分析表明重建序列对于采样点周边较大范围地区4~7月降水量变化特征均具有很好的代表性。与海温数据空间相关分析显示,降水重建序列与太平洋海温呈显著正相关。多窗谱分析和小波分析表明,重建序列存在2.1、2.5、2.8、4.1、7.0和63.7年的显著周期(p<0.01)。表明研究区域降水变化在多年代际尺度上可能受到ENSO和PDO的影响。

The northern region of the Greater Khingan Mountains is one of the sensitive areas affected by climate change,and due to the relatively short-term measurement data,there is still a weak understanding of interannual and interdecadal regional precipitation variability.To evaluate the strength and frequency of similar events,and our understanding of historical climatic regimes of Northeastern China,it is important to obtain a longer record of past climatic variations.Tree-ring cores of Pinus sylvestris were collected in the Mangui Town in Hulunbuir City,Inner Mongolia Autonomous Region(52°04′N,122°11′E;710 m).The forest resources in the Mangui Forest Area are rich and widely distributed,and tree species mainly include Larix gmelini,Betula platyphylla,Populus davidiana,and Pinus sylvestris.The forest soil is mostly brown coniferous soil with a small amount of dark meadow soil and swamp soil,and the soil layer thickness is about 30 cm.A total of 55 core tree rings of Pinus sylvestris were collected using an increment borer and a tree ring width chronology was established.Cores were brought to the laboratory and air-dried prior to mounting and sanding;all samples were prepared following standard dendrochronological techniques.Tree-ring widths were measured to 0.01 mm using a LINTAB^(TM) 6.0 measuring system.The width measurement and cross-dating accuracies were verified using COFECHA.Correlation analysis showed that the precipitation in spring and early growth season was the main limiting factor for the radial growth of Pinus sylvestris var.mongolica in Mangui area.The radial growth of trees had the highest correlation with the precipitation(r=0.549,p<0.001)from April to July in the current year.A single linear regression model was used to reconstruct the precipitation from April to July of the current year in this area for the past 242 years.The reconstruction equation explained 30.1%of the variance of the precipitation.The equation successfully passed the leave-one-out methods,which indicated that the reconstructed sequence results were stable and reliable.In the past 242 years(1776~2017,EPS>0.85),there were five wet periods(1788~1805,1841~1871,1887~1899,1926~1966 and 1993~2000)and six dry periods(1776~1787,1806~1840,1872~1886,1900~1925,1967~1992 and 2001~2017).1900~1925 was the worst drought in the study area in the past 242 years.The dry and wet periods of reconstructed precipitation were in good agreement with the results of other comparison series.Spatial correlation analyses with a gridded precipitation dataset showed that our precipitation reconstruction sequences had a good representation for the variation of April-July precipitation in northern Greater Khingan Range.In addition,the spatial analysis with SST data also showed that the precipitation reconstruction sequences from this study were significantly positively correlated with SST in the Pacific Ocean.Power spectrum and wavelet analysis showed that the reconstruction sequence had significant periods of 2.1,2.5,2.8,4.1,7.0 and 63.7 years(p<0.01).In summary,the change of precipitation from April to July in the study area can be related to some large-scale climate oscillations,such as El Niño-Southern Oscillation and Pacific Decadal Oscillation.