大别山1846—2010年干湿变化记录——来自树轮宽度的证据

Tree-ring records revealed the dry/wet variation of the Dabie Mountains during 1846-2010

中国亚热带地区树轮气候学研究已取得较大进展,但气候重建基本都集中在温度方面,基于树轮宽度的水文气候研究鲜有成果,不利于全面理解亚热带地区历史气候变化特征。本文基于北亚热带大别山地区黄山松树轮宽度年表与气候要素的相关分析,发现树轮宽度指数与上一年_(4-7)月平均相对湿度显著负相关(r=−0.68,p<0.01)。在此基础上,重建了大别山地区1846—2010年_(4-7)月平均相对湿度变化历史。重建序列方差解释量达到46.4%(调整自由度后为45.3%)。在整个重建时段中存在3个湿润期(1891—1903年,1905—1921年和1950—1993年)和3个干旱期(1868—1890年,1922—1934年和1994—2005年)。同时,重建序列与采样地周边区域旱涝指数以及天目山的相对湿度重建序列在年代际尺度上高度相关,说明过去165年间中国东南亚热带较大区域范围内的干湿变化在年代际尺度上较为同步。空间分析结果表明重建序列也能够在一定程度上指示研究区及周边较大区域范围内的土壤湿度变化。综上,利用树轮宽度指标重建的大别山的相对湿度变化为研究亚热带地区干湿演化历史提供了参考依据,完善了时间尺度上亚热带地区相对湿度数据,同时也证实了亚热带1990年以后干旱化趋势的出现。

Background,aim,and scope In the context of climate change,the warm and dry climate continues to spread across the subtropical regions.To understand the wet and dry evolution of the past climate,different moisture indicators need to be investigated.Research on relative humidity(RH)helps to better understand the response of trees to moisture signals in the subtropics.In this study,a tree-ring width chronology was applied to reconstruct the RH of the Dabie Mountains(DBS)from previous April to previous July.Materials and methods The treering width chronology of Pinus taiwanensis in Tiantangzhai(31°06′36″—31°07′12″N,115°42′—115°48′E,1550 m a.s.l),DBS,was obtained from 47 cross-dated tree-ring width measurements(Cai et al,2018).Pearson correlation analysis was adopted to analyze the relationship between tree-ring width growth and various climate signals,e.g.,RH,SPEI(Standardized Precipitation-Evapotranspiration Index),PDSI(Palmer Drought Severity Index)and soil humidity.RH was selected for reconstruction by using a simple linear regression equation.The high-frequency relationship between the reconstruction and the observed data was subjected to the first-order difference test.The reliability of the reconstruction was tested using the Bootstrap and Jackknife methods.Spatial analysis(http://climexp.knmi.nl/)and comparative analysis were performed to explore the spatial and temporal representativeness of the reconstruction.Results Current study revealed that the negative correlation between tree-ring width index and RH from previous April to previous July(RH_(p4-7))was statistically significant(r=−0.68,p<0.01).Based on the simple linear regression equation(RH_(p4-7)=−7.4106×STD+83.2145),April—July RH for the period 1846—2010 was reconstructed.The reconstruction explained 46.4%of the instrumental variance(45.3%after adjusting the degree of freedom).Three wet periods(1891—1903,1905—1921,and 1950—1993)and three dry periods(1868—1890,1922—1934,and 1994—2005)were identified from the reconstruction.Discussion At high altitudes,the negative correlation between RH and tree-ring width might be driven by sustained high temperatures in summer which increased the relative humidity of the air.Since higher water vapor pressure suppressed evapotranspiration,the sensitivity of trees to moisture was reduced.Comparisons of the reconstruction with April—June RH in the Tianmu Mountains(TMS),Zhejiang Province and the dry/wet index(DWI)near the study area(Wuhan,Hefei,and Anqing)indicated high coherence at decadal scales.The correlation coefficient between our reconstruction and TMS April—June RH was 0.32(n=165,p<0.01).On the 11-a(r=0.68,p<0.01)and 21-a scales(r=0.74,p<0.01),the wet/dry variations of the two places were relatively consistent.Also,at 11-a and 21-a scales,the reconstructed RH significantly correlated with the DWI record,with r value of 0.42 and 0.42,respectively(p<0.01).Conclusions The positive correlation between RH and tree-ring width chronology in the DBS from previous April to previous July was statistically significant.The reconstructed RH indicated evident annual to decadal variations during 1846—2010.At decadal scale,the reconstructed RH_(4-7)in the DBS could represent the moisture condition of the southeast China over the period 1846—2010.Recommendations and perspectives RH of the DBS reconstructed using the tree-ring width index should provide a reference about the history of dry and wet evolution in the southeast China,and confirm its subtropical aridity trend in recent decades.