A 2917-year tree-ring-based reconstruction of precipitation for the Buerhanbuda Mts., Southeastern Qaidam Basin,China

In this study, we developed the tree-ring width chronology for the period of 1404 BCE to 2015 CE using Qilian juniper (Sabina przewalskii Kom.) trees collected from the Buerhanbuda Mts. in the southeastern Qaidam Basin (QB) near Nuomuhong Village, Qinghai Province. This is the first and longest chronology to date in this region. Based on the relationships between the tree-ring width chronology and climate data, the annual precipitation from previous July to current June (July-June) was reconstructed for the past 2917 years from 902 BCE to 2015 CE. This reconstruction accounted for 47.9% of the total variance in the actual July-June precipitation in the calibration period (1957–2015). The full reconstruction captured distinct wet and dry variability, and contained evidence of some low-frequency climate signals. We identified 13 wet and 12 dry periods, of which 1443–1503 CE and 1789–1836 CE were the two longest dry periods. General agreements in the low-frequency variations between the July-June precipitation and other moisture-sensitive records for the northeastern Tibetan Plateau (TP) suggested that the reconstruction in this study represented a regional signal. Spatial correlations with gridded precipitation data also indicated that the reconstructed July-June precipitation could adequately represent climate fluctuations over a large area of the northeastern TP. The new tree-ring width chronology and precipitation reconstruction are important for understanding natural climate change in the southeastern QB.     

May–June drought reconstruction over the past 821 years on the south-central Tibetan Plateau derived from tree-ring width series

Knowledge of drought variability and their possible mechanisms during the past hundred years is still limited in the mountainous region of south-central Tibetan Plateau (TP). In this study, a long-term tree-ring width chronology dating back to 1190 CE was combined using 328 increment cores from the Nagqu region. Based on the relationships between this tree-ring width chronology and climate data, we reconstructed May–June self-calibrated Palmer Drought Severity Index (scPDSI) for the past 821 years (1190–2010 CE). Additional comparisons with other available precipitation or drought reconstructions were conducted. We further investigated the influence of the South Asian summer monsoon (SASM) on the drought variability in our study region. Results indicated that our tree-ring width chronology contained stable drought signal in the early summer season (May–June). During the past 821 years, the longest dry and wet periods lasted for 116 and 90 years, respectively, based on a 21-year Fast Fourier transform filter. Specifically, longer than ten years’ dry periods prevailed during 1211–1245 CE, 1280–1358, 1421–1471, 1500–1571, 1580–1598, 1650–1691, 1782–1807 and 1867–1982; while wet intervals occurred in 1190–1210 CE, 1246–1279, 1359–1420, 1472–1499, 1599–1649, 1692–1781, 1808–1866 and 1983–2010. Generally consistent dry and wet intervals across the southern TP were found by comparisons with other available datasets during their common periods. Interestingly, we detected an unstable influence of the SASM on the May–June drought variability in our study region, at least for the past three and a half centuries. This study therefore gives a new perspective of drought variability as well as their relationships with the SASM over a long-term period on the south-central TP.     

Dry/wet variations in the eastern Tien Shan (China) since AD 1725 based on Schrenk spruce (Picea schrenkiana Fisch. et Mey) tree rings

Cores of Schrenk spruce from seven sites of eastern Tien Shan were used to develop a regional tree-ring chronology to extend the climate record. We developed an August–July Standardized Precipitation Evapotranspiration Index (SPEI) reconstruction that spans AD 1725–2013 based on the regional tree-ring chronology. The reconstruction model accounts for 45.3% of the SPEI variance from 1959 to 2013. The SPEI reconstruction agrees reasonably well with the dry and wet periods previously estimated from tree rings in northern Xinjiang. The correlation analysis revealed that temperature plays an important role in regional drought variability, and some extreme wet years also coincide with the volcanic eruptions.     

川西雅江地区过去567年3—8月干旱变化的树轮重建

使用零信号去趋势法建立了四川甘孜州拉日玛采点川西云杉标准化树轮宽度年表。结果表明: 云杉树轮年表与雅江3—8月一个月时间尺度的标准化降水蒸散指数(SPEI1)间存在显著正相关。由树轮年表当年与次年序列重建了雅江地区1442—2008年3—8月SPEI1指数变化,方差解释量达42.8%。重建序列主要揭示了历史时期SPEI1的低频变化。川西雅江地区3—8月SPEI1在过去567年中存在1442—1465年、1516—1601年和1836—2008年3个偏湿阶段,位于其间的为2个偏干阶段;重建序列在1455—1762年间存在显著变干趋势,而1833—1950年具有显著变湿趋势,1959—2008年的变湿趋势最为明显;3—8月SPEI1重建值在1512、1733、1767、1831、1941、1957和1975年发生了从干旱向湿润的突变,而在1684年与1961年则相反。与周边气候重建序列的对比显示,川西雅江地区3—8月SPEI1重建序列的低频变化与青藏高原东北部年降水量和祁连山东段北坡SPEI05指数的变化具有一定相似性。该重建序列对青藏高原东部及青海南部的3—8月SPEI1变化具有较好的代表性。     

基于树轮宽度数据重建的阴山东部过去399年降水变化

基于阴山东部油松树轮样芯,建立采样区域树轮宽度年表,并计算器测时期(AD 1952—2007)月均温和月降水量与树轮宽度年表的相关系数。结果表明: 树轮宽度年表与上一年9月至当年6月降水量变化的相关性最高(r=0.73,n=56,P<0.01),基于此重建了阴山东部过去399年(AD 1619—2017)上一年9月至当年6月的降水量变化历史。该重建解释了器测时期上一年9月至当年6月降水量54.9%的方差,经“留一法”交叉验证和分段独立检验证明,重建方程稳定可靠。在年代际尺度上,过去399年存在4个湿润时期(AD 1619—1663、AD 1705—1711、AD 1945—1963和AD 1979—2017)和4个干旱时期(AD 1734—1767、AD 1786—1814、AD 1839—1867和AD 1888—1942)。其中,AD 1979—2017是最湿润的时期,而AD 1888—1942是干旱持续最长的时段,包含最干旱时期1920s晚期。功率谱分析显示,过去399年该区降水具有2～7年和125年准周期变化。通过与邻近区域重建对比及空间相关分析表明,本降水重建序列可以较好地代表研究区域的降水变化。     

呼伦贝尔沙地樟子松年轮生长对气候变化的响应

以内蒙古呼伦贝尔地区沙地樟子松为样本,建立了樟子松树木年轮宽度年表,应用相关分析和响应函数分析等年轮气候学方法,研究了樟子松径向生长对气候变化的响应。结果表明,樟子松年轮宽度与4月和6—9月平均温度呈显著负相关关系(P<0.05);与各月降水量多呈正相关关系,特别是与当年5—8月的月降水量呈显著正相关关系(P<0.05);树轮年表与前一年10月至当年10月的PDSI均呈显著正相关关系(P<0.05),其中与5月份PDSI的相关性最高。响应函数分析表明,年表与当年6—7月的平均气温、上一年10月和当年5—7月份的降雨存在显著的相关性,与5—7月份PDSI存在较显著的正相关性;综合来看,呼伦贝尔沙地樟子松生长同时受降水和温度的影响,其径向生长与气候因子间的关系属于降水敏感型,为区域降水重建提供了科学基础。     

江西大岗山地区7-9月降水量的重建与分析

根据江西大岗山地区4个采样点的马尾松年轮样本,建立了本地区的综合年轮年表,分析了马尾松径向生长与气候因子变化的相关及响应关系,发现大岗山地区树木径向生长受生长季7—9月降水量影响较显著,呈负相关关系。在响应分析的基础上,首次重建了大岗山地区1892年以来7—9月的降水量,交叉检验表明重建序列是可靠的。重建结果表明,大岗山地区7—9月份降水变化在过去的117年中总体经历了3个偏干时期：1895—1902年,1908—1926年和1944—1985年,和3个偏湿阶段：1903—1907年,1927—1943年及1986—2008年。重建的降水量序列在1921年,1937年及1977年发生明显的方差突变,表明百年以来该地区降水量变化趋势存在阶段性变化。     

Tree-ring based December–February precipitation reconstruction in the southern Zagros Mountains,Iran

We developed the first tree-ring width chronology from Quercus brantii Lindel for the period 1796–2015 in the southern Zagros Mountains, Iran, using standard dendrochronological procedures. Climate-growth relationships revealed that DecemberöFebruary precipitation has strong positive effects (r = 0.66; P < 0.01) on the species’ growth while mean temperature during the growing season has strong negative effects. Spatial correlations with Palmer Drought Severity Index (PDSI) and gridded precipitation data revealed that the chronology contains regional climate signals and tree growth variations may represent precipitation fluctuations over large areas of the Middle East. The linear regression model accounts for 44% of the actual DecemberöFebruary precipitation variance. The reconstructed precipitation revealed that over the period 1850–2015 extreme dry years occurred in 1870-71, 1898, 1960 and 1963-64, and extreme wet years occurred in 1851, 1885, 1916 and 1921 in the southern Zagros region. The longest dry period lasted 16 years and occurred from 1958 to 1973. Two-year consecutive wet and dry events showed the highest frequencies and the average length of dry and wet events were 2.9 and 3.6 years over the reconstructed period. Correlations between the long-term reconstructed precipitation and the North Atlantic Oscillation (NAO), Southern Oscillation Index (SOI), and Pacific Decadal Oscillation (PDO) confirmed the effects of teleconnection patterns on precipitation in the southern Zagros region.     

Drought signal in the tree rings of three conifer species from Northern Pakistan

Anthropogenic and climatic stressors have affected the forests of northern Pakistan in recent decades. Several studies have been conducted to understand forest growth and its relation to the changing climate in this region, but more work needs to be done to understand this complex environment. In this study, we have collected tree core samples of three conifer species (Pinus wallichiana, Picea smithiana, and Abies pindrow) from three different sites in northern Pakistan to understand their radial growth pattern with the goal of finding a relationship between ring-width and climatic parameters (temperature, precipitation, and drought). A 610-year (AD 1406–2015), a 538-year (AD 1478–2015), and a 306-year (AD 1710–2015) long tree-ring width chronology of Pinus wallichiana, Picea smithiana, and Abies pindrow were developed, respectively, using living trees. The ring-width chronologies of these three species showed a strong positive link with the self-calibrated Palmer Drought Severity Index (scPDSI) rather than precipitation or temperature alone, indicating that soil moisture is the primary limiting climatic factor for the growth of these species in the sampling locations. The chronologies of Pinus wallichiana and Picea smithiana exhibited growth suppressions during AD 1570–1610 and the second half of 17th century while their growth was heightened from AD 1540–1560. We have found the lowest growth in Abies pindrow and Picea smithiana from AD 1900–1920, suggesting dry conditions. All three chronologies have exhibited the most rapid increase in growth during the recent decades, suggesting that this region is experiencing climate change with a strong trend towards wetter conditions.     

Rain in the desert; A precipitation reconstruction of the last 156 years inferred from Aleppo Pine in the Bardenas Natural Park,Spain

Understanding the regional hydroclimatic variability beyond the instrumental period is essential to contextualize the current climatic period within a longer record. Dendrochronology has been used as a powerful tool for estimating the temperature and precipitation variability of the last centuries on an annual and even seasonal scale. However, most of the centenary trees in Spain are located in high-elevation mountain environments, so the reconstructed signal is not representative of the climate variability of the lowlands, where the main cities and most of the population and human activities are located. Here we present a precipitation reconstruction of the Bardenas Natural Park, a semi-arid environment within the Ebro Valley, based on 61 new tree-ring width series of Pinus halepensis Mill. The new chronology, calibrated against high-resolution instrumental precipitation data, uncovers a high and robust relationship with the annual precipitation (from previous June to current May) (1951−2012 CE; r = 0.78;), representing the precipitation totals of the hydrological year. Our reconstruction explains 61 % of the annual precipitation for the period 1951−2012 and is representative of the lowlands of the Northeast of Spain. We identified 12 extremely dry and 11 extremely wet years, finding the first half of the 20th century to be the period with most extreme episodes of the reconstruction. Additionally, we found a strong agreement between our tree-ring based reconstruction and the lowlands documentary-based drought estimators (rogation ceremonies). These findings contribute to improving our understanding of past hydroclimatic variability in semi-arid lowland areas where available proxy records are rare.     

河西走廊植被净初级生产力时空变化及其影响因子研究

干旱半干旱区植被NPP变化对全球碳循环有重要影响,该区域NPP对气候变化的响应表现出较大的时空异质性,其驱动机制并不十分清楚。选择中国河西走廊,利用随机森林算法估算了2002-2018年的NPP,基于偏导数法计算了气候与人类活动对NPP的影响。结果表明：（1）随机森林算法能较好的适用于干旱半干旱区NPP估算。（2）2002-2018年间河西走廊年NPP的平均值为153.32 gC m^-2 a^-1,总量为37.468 Tg C/a,呈东南向西北递减的分布特征,研究期间NPP呈2.37 gC m^-2 a^-1（P=0.09）增长趋势。（3）河西走廊NPP变化52.51%由气候因子贡献,47.49%由人类活动贡献。（4）在气候变化对NPP的影响中,降水主导了该区72.21%的区域,温度对NPP变化量的贡献占73.71%,前者影响着NPP变化格局,后者主导NPP变化数量。升温和增湿均有利于该区NPP增加,随着西北地区气候暖湿化,河西走廊植被会持续改善,该研究有助于理解干旱半干旱区NPP对气候变化的响应机制,为适应气候变化政策制定提供理论依据。     

树轮记录的贺兰山区近百年来的干旱事件

利用采自东亚夏季风最北缘、地处干旱-半干旱地区的贺兰山区的树轮样芯,建立了贺兰山地区最近93年来的树轮宽度年表。与气象观测记录的相关分析结果表明,降水是限制贺兰山区树木生长的主要因素,其中5~7月份的降水与树轮宽度呈显著正相关关系,相关系数为0.522(通过95%的信度检验)。在贺兰山的树轮宽度记录中有两个主要的低生长期即20世纪20年代和70年代末到90年代末,这两个低生长期均与该区域的干旱事件相对应。通过分析还发现在干旱事件中不仅出现低降水而且同时与高气温相伴。也就是说在干旱时期内,高温和低降水的水热组合对树木影响十分显著,从而由单纯降水减少变为一种低降水高蒸发的环境,加剧了气候的干旱程度从而使树木生长出现低的生长期,形成窄轮。这种水热组合引起树轮宽度的变化对于理解过去干旱事件及其过程具有重要意义。     

Climatic signal in growth-rings of Copaifera lucens: An endemic species of a Brazilian Atlantic forest hotspot,southeastern Brazil

In this study, we present the first tree-ring chronology for the tropical tree species Copaifera lucens and its climatic signal in southeastern Brazil. Tree-ring width series were compared with local climate indices using a drought index (Standardized Precipitation Evapotranspiration Index —SPEI), in monthly, bi-monthly and four-monthly scales. We also calculated negative pointer years over the time-span of the tree-ring width. The radial growth of C. lucens showed a positive correlation with the SPEI of the current summer and autumn in all the three analyzed time scales, while the negative pointer years matched with drier years. The species was highly sensitive to very low summer precipitation, which may lead to a 49% reduction in growth. We conclude that the long-living C. lucens has a great potential for dendrochronological studies as it shows a marked climatic signal. Our study also reinforces the importance of rainfall in regulating radial growth in tropical forests and sheds light on the local climate influence on tree growth in recent decades.     

Streamflow reconstruction of Eastern Himalaya River,Lachen ‘Chhu’, North Sikkim,based on tree-ring data of Larix griffithiana from Zemu Glacier basin

The relationship of streamflow records of the Lachen River with tree-ring parameters of total tree-ring width (TRW), earlywood width (EWW) and latewood width (LWW) chronologies of Larix griffithiana from Lachen, North Sikkim, Eastern Himalaya was generated. These chronologies correlate significantly with the observed discharge of the Lachen River where the EWW chronology explains 61.2% of the streamflow variance. Based on this result, Lachen River discharge for the period of previous year March to current year February was reconstructed using EWW chronology, which extends back to AD 1790. In the smoothed reconstructed data the period of extreme low streamflows were during AD 1791–1805, 1813–1822 and 1914–1925 and the extreme highs were during AD 1823–1835, 1879–1890, 1926–1946 and 1980–1989. The streamflow is also found to be lower than average during the monsoon failure (or East India Drought) of AD 1792–1796 and past great droughts of AD 1876–1878. The lower tree growth during AD 1816–1822 is consistent with that of the Tambora volcanic eruption of Indonesia in AD 1815. High spectral power at 4–8 years in the reconstructed streamflow is similar to that of ENSO range.     

Two climate‐sensitive tree‐ring chronologies from Arnhem Land,monsoonal Australia

The ecology of the Australian monsoon tropics is fundamentally shaped by dry conditions between May and October followed by highly variable rainfall over the months of November to April. Due to its crucial ecological importance, a better understanding of past hydroclimate variability in the region is of great interest to land managers and custodians in this region. Short instrumental records also make highly resolved terrestrial palaeoclimate records for northern Australia prior to 1900 CE of considerable scientific importance. Here, we present two new well‐replicated Callitris intratropica ring‐width chronologies from Arnhem Land in northern Australia, one of which extends the tree‐ring record in the region by another 86 years, back to 1761. Both chronologies have clearly defined regional patterns of correlations with temperature, precipitation, potential evapotranspiration and two drought indices (the self‐calibrating Palmer Drought Severity Index (PDSI) and the Standardised Precipitation Evapotranspiration Index (SPEI)) across the lower latitudes of the Northern Territory. Results indicate considerable scope for hydroclimatic reconstructions based on C. intratropica for transitional periods into and out of the wettest time of the year. This suggests that such reconstructions would reflect variability in the duration of the wet period. While precipitation or streamflow reconstructions may be possible for both these transitional periods, drought reconstructions will be best focused on the months of March–May at the end of the wet period. Hydroclimate reconstructions would provide important baseline information for understanding the rate and magnitude of current regional climate change for these ecologically and culturally important transitional periods.     

祁连山中部地区树轮宽度年表特征随海拔高度的变化

利用采自祁连山中部地区不同海拔高度的四个采样点的青海云杉树轮样芯 ,分别建立了树木年轮宽度年表。发现随海拔高度的上升 ,树轮宽度指数的振幅减小 ,年表的平均敏感性降低 ,样本间的一致性也逐步减小 ,上限年表与气候因子的相关性最低 ,这与目前大家普遍认同的上限树木的生长受温度控制的概念并不一致。进一步的分析表明 ,年表的敏感性随海拔高度降低主要是由于该区域树木生长的限制因子是春季降水 ,而降水随海拔高度的升高而增加 ,从而使得春季降水对树木生长的限制作用随海拔升高而逐步减弱 ;生物学指标的测定结果表明 ,生长在高海拔的树木对环境的生态适应策略发生变化 ,其生理代谢维持在较低水平 ,以避免环境变化带来的影响 ,因此生长在高海拔的青海云杉对环境变化的敏感性较差。     

Establishment of a 4650-year-long eigenvalue chronology based on tree-ring cores from Qilian junipers (Juniperus przewalskii Kom.) in Western China

This paper describes a tree-ring width chronology that spans the past 4650 years, established using the recently developed eigenanalysis technique. The aim is to show whether this eigenanalysis method enables the extraction of long-term tree-growth variations that are due to climatic changes, from a large dataset comprising 1263 tree-ring width records sampled from the highlands of Western China. In order to exclude the so-called growth rate/life span association effect, tree-ring width records were sorted into six subsets, based on the life spans of the trees sampled: 200–400, 400–600, 600–800, 800–1000, 1000–1500 years old, and trees older than 1500 years. Some partial chronologies were created, by pairing the set of all tree samples (living, dead, archaeological remains) with the living trees belonging to each subset. We computed the contours of tree-growth variations (on both 100-year and longer time scales) for each subset, ending with six pairs of these partial subset chronologies. Two sums of all these partial chronologies thus yielded a record of precipitation variations over a period ranging from 2627 BCE up to 2012 CE. It was found that this record shows a high degree of similarity to the existing chronology produced using the regional curve standardization (RCS) method applied to the same dataset, indicating that the eigenvalue chronology is capable of faithfully extracting long-term climatic variations. This also confirms that the first eigenvector represents the growth pattern that is characteristic of each biologically unique tree as well as the micro-environment of each tree stand. The variations observed over the last millennium seem to be connected to a cycle of solar activity with a period of ∼200 years. However, a clear lack of correspondence between solar activity and tree growth prior to 1000 CE indicates that the recent consistency may be coincidental. We believe that the eigenanalysis technique is readily applicable to other kinds of tree-ring datasets from different parts of the world.     

Development of tree-ring width chronologies and tree-growth response to climate in the mountains surrounding the Issyk-Kul Lake,Central Asia

Three tree-ring width chronologies were developed from 75 Picea schrenkiana trees ranging from low- to high-elevation in the mountains surrounding the Issyk-Kul Lake, Northeast Kyrgyzstan. The reliable chronologies extend back to the mid-18th and late-19th centuries. Spatial correlation analysis indicates that the chronologies for the relatively high-elevation trees contain large-scale climatic signals, while the chronology at relatively low elevation may reflect the local climate variability. The results of the response of tree growth to climate show that these chronologies contain an annual precipitation signal. Furthermore, the influence of temperature indicates mainly moisture stress that is enhanced with rising elevation. The tree-ring records also captured a wetting trend in eastern Central Asia over the past decades. These new tree-ring width chronologies provide reliable proxies of precipitation variability in Central Asia and contribute to the International Tree-Ring Data Bank.     

基于油松树轮重建晋东南地区近296年来1—6月降水变化

区域历史气候变化研究受观测数据限制,不利于认识长时间尺度上气候变化情况。本研究采用山西省东南部油松树轮样芯,建立采样区树轮年表,分析降水变化与树轮宽度年表之间的关联。结果表明: 树轮差值年表(RES)与1—6月的降水量变化有较好的相关性,(r=0.636,n=59,P<0.01)。采用线性回归方法分析山西省东南部区域1724—2019年1—6月的降水重建序列,方差解释量为40.4%,经检验重建方程稳定可靠。对降水重建序列特征分析表明,1724—2019年存在10个极端干旱年和6个极端湿润年,经历了6次干旱期(1742—1771、1830—1848、1872—1894、1917—1945、1961—1981和1990—2019年)、4次湿润期(1727—1741、1772—1829、1849—1871和1895—1916年)。最长干旱期为1742—1771、1990—2019年,最长湿润期为1772—1829年。对于过去296年,降水变化序列存在2.3、3.2～3.3、3.7～3.8、6.3～6.7和8.3～8.7年周期变化特征,其中2.3年的周期与“准两年脉动”周期重合,3.2～3.3、3.7～3.8和6.3～6.7年的周期可能与厄尔尼诺和南方涛动的变化存在一定关系。空间相关分析表明,重建降水序列能够较好地代表研究区域范围的降水变化。