王亚军
, 马玉贞
WANG Yajun, MA Yuzhen
收稿日期: 2015-12-17
修回日期: 2016-03-14
网络出版日期: 2016-04-20
版权声明: 2016 《地理研究》编辑部 《地理研究》编辑部
基金资助:
作者简介:
作者简介：王亚军（1973- ）,女,辽宁凌源人,博士,主要研究方向为环境演化。E-mail: hbyjwang@163.com
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摘要
NDVI能够反映地表覆盖和生态环境变化。在祁连山东延余脉采集树轮样本,分析树木径向生长与植被NDVI的相关关系,并重建历史时期植被NDVI变化。结果表明：树木径向生长与夏季NDVI受到水热条件变化的显著影响,且树轮宽度与夏季NDVI显著正相关,采用简单线性回归方法建立二者的拟合方程,方差解释量达0.600（R2adj=0.582,F=34.472,P<0.0001）;公元1845年以来,重建的NDVI序列显示植被覆盖相对较低时期有19世纪60年代,80年代初期,20世纪初期和20-30年代,其中20世纪20-30年代NDVI低值期与中国北方大范围旱灾一致;重建的NDVI与旱涝指数显著负相关,证实重建NDVI序列的可靠,且显示该区旱涝演化趋势;周期分析表明公元1845年以来,NDVI序列存在2-3年、5年左右、13年左右和15年左右的振荡。
关键词：
Abstract
Normalized Difference Vegetation Index (NDVI) can reflect land cover and the ecological environment change. This study sampled tree-ring cores in the Xinglong Mountain -the eastward extension of the Qilian Mountains, analyzed the correlation relationship between tree radial growth and vegetation NDVI, and reconstructed NDVI variability. The results indicated that tree radial growth and summer NDVI were influenced significantly by hydrothermal condition in the study area, the tree-ring width correlated significantly and positively with summer NDVI, the fitted equation relating them was developed by using simple linear regression, and the explained variance of the reconstruction was 0.600 (R2adj = 0.582, F = 34.472, P < 0.0001). The summer NDVI reconstruction since 1845 AD showed that vegetation coverage was relatively sparse in the 1860s, the early 1880s, the early 20th century and 1920s-30s, and the low period 1920s-30s corresponded to the megadrought that occurred widely in northern China. The NDVI reconstruction correlated significantly and negatively with the dryness/wetness index, which showed the reliability of the reconstructed NDVI and also some representation of the wet-dry evolution model. Cycle analysis showed that the NDVI sequence has presented 2-3 years, about 5 years, about 13 years and about 15 years of oscillation since 1845 AD.
Keywords：
植被对气候变化敏感,地表植被覆盖变化对气候的响应成为当前科学界关注的热点问题之一。由遥感图象红和近红外波段反射率值确定的归一化植被指数（Normalized Difference Vegetation Index,NDVI）是指示植被覆盖和植被生产力的良好指标[1,2],被广泛用于研究植被覆盖的时空变化[2,3]、植被变化对气候的响应[4]、对沙尘天气的影响[5]等。但实测NDVI数据仅开始于20世纪80年代,无法满足研究过去长时间尺度地表植被覆盖变化的需求,因此回溯历史时期地表植被NDVI变化得到越来越多的关注。
树木年轮资料具有时间序列长、分辨率高（年或者季节）、连续性强等优势,在全球变化研究中广泛用于气候要素重建[6-10]。目前,树轮指标正逐步应用于植被NDVI变化方面。研究发现,树木生长与植被NDVI相关性较好,径向生长能够衡量植被NDVI变化[11-16]。研究成果显示树木年轮在研究植被NDVI变化中的巨大潜力,不过也发现北亚热带地区树木径向生长不能很好反应NDVI的变化[17]。
研究区兴隆山属于祁连山东延余脉[18],森林茂密。Fang等[19]基于兴隆山青杄树轮宽度,分析其与气温、降水和PDSI相关关系,并重建公元1794年以来年PDSI的变化序列。这些研究都在不同侧面利用树轮技术分析NDVI变化,但利用树轮技术,借助NDVI重建历史植被变化的研究很少,尤其是如何利用树轮方法在反演更长时间范围内NDVI变化基础上研究植被覆盖变化的规律和机理更是具有一定的前瞻性,因此本文将探讨兴隆山树木年轮宽度与地表植被覆盖关系,利用兴隆山树轮资料重建高分辨率的地表植被NDVI,分析植被覆盖变化规律。本文的研究将有助于了解全球变化背景下的当地生态环境演变,为预测该区域生态环境变化规律和演变机理提供可以参考的依据。
兴隆山植物种类繁多且垂直地带分布明显。随着海拔增加,植被类型依次出现森林、高山灌丛、草甸和荒漠自然景观。森林树种以云杉（Spruce）、油松（Pinus tabulaeformis）、落叶松（Larix gmelinii）、杨（Populus tremula）、桦（Birch）和栎（Oak）等为主。
树轮样本采集时间为2008年5月,树种为青海云杉（Picea crassifolia）和油松（Pinus tabulaeformis）（35º47'N,104º04'E）。青海云杉（Picea crassifolia）分布于海拔2550 m左右,树木高度一般在15~20 m,胸径25~50 cm。用内径为5.3 mm的生长锥,在树干1 m左右高度处,从不同方向钻取1~2根树芯,共采集14棵树,24个样芯。油松（Pinus tabulaeformis）,分布于海拔2450 m左右,在树干大约1 m左右高度处,从不同方向钻取2根树芯,个别树钻取3根芯,共采集19棵健康立木,41根树芯。研究区示意图（数据来源于http://www.gscloud.cn）如图1所示。
图1 采样点和气象站点分布
Fig. 1 Map showing tree-ring sampling site and meteorological station
所有树轮样本经过晾干、固定、磨平打光以及初步目测定年,采用分辨率0.01 mm的LINTAB年轮宽度测量仪测量树轮宽度。利用COFECHA程序[20]检验交叉定年和测量结果,发现油松和云杉年轮宽度变化相关性较高,因此将所有样本合并在一起进行分析。通过判断各序列与主序列之间的差异大小,剔除5根与主序列相关系数小、奇异点多的样芯。考虑到样本年龄长短不同,部分油松植于20世纪70年代末期,所以在去生长趋势过程中,采用负指数函数或线性函数,以及步长在1/3~2/3的样条函数,逐条检查,反复试验,选择理想的函数拟合生长趋势,最终通过ARSTAN程序[21]建立树木年轮标准化（STD）年表和差值（RES）年表（图2）。年表各项参数值如表1所示。
图2 树木年轮年表（实线）和样本量（虚线）（a. STD,b. RES;箭头指向Csss大于0.85的年份）
Fig. 2 The tree-ring width chronologies (continuous line) for the STD (a) and RES (b) chronologies and sample depth (dotted lines). The arrows points to the year since the coefficient of subsample signal strength (Csss) > 0.85
表1 年表各项参数统计值
Tab. 1 Statistics for the chronologies
| XLSSTD | XLSRES | |
|---|---|---|
| 敏感度 | 0.175 | 0.197 |
| 标准差 | 0.242 | 0,170 |
| 公共区间 | 1925-2007 | 1925-2007 |
| R1 | 0.269 | 0.420 |
| R2 | 0.492 | 0.663 |
| R3 | 0.255 | 0.405 |
| SNR | 5.873 | 11.592 |
| EPS | 0.855 | 0.921 |
| Csss>0.85（芯） | 1861(8) | 1845(5) |
从表1中各项统计参数值,可以看出RES年表各统计参数值均高于STD年表。RES年表的敏感度、相关系数和信噪比值都较高,样本代表性高达0.921,年表包含的气候变化信息较多,能够利用其宽窄变化进行树轮气候学研究。
所使用的GIMMS NDVI数据为荷兰皇家气象研究所的数据共享网站（http://climexp.knmi.nl）提供的逐月平均NDVI数据集,空间分辨率为0.22°×0.22°,时间段为1981年7月-2006年12月。本文从该数据集中提取出树轮采样点周围0.5°×0.5°范围内的逐月平均NDVI值,建立1981年7月-2006年12月每月NDVI数据序列。
选取距离树轮采样点最近的榆中气象站点（35°52′N,104°09′E,1874 m）记录的逐日降水和气温资料。将逐日降水和气温按月分别进行计算,得到1981-2007逐年所有月份的月总降水量和月均温值。该站平均年降水量为375.9 mm,降水集中在6-8月,占全年降水量的53.5%,年均温6.9℃,7月气温最高,为19.2℃。另外还选取榆中气象站记录的扬沙和沙尘暴天气日数资料。
采用的帕默尔干旱指数（Palmer Drought Severity Index,PDSI）来源于荷兰皇家气象研究所的数据共享网站（http://climexp.knmi.nl）,空间分辨率为0.22°×0.22°,时间段为1901年1月-2012年12月。以树轮采样点为中心,提取其周围0.5°×0.5°范围内的逐月平均PDSI序列。
考虑到NDVI数据的起始时间,将降水,气温,沙尘数据和PDSI数据的时间范围统一为1981-2006年。
采用相关函数分析树轮宽度、植被指数和水热状况间的线性相关程度,以探讨树木径向生长与植被NDVI变化的影响因素,以及二者间的相关性。考虑气候要素对植被生长具有滞后效应,相关分析过程中,降水、气温和PDSI数据选取时段为前一年6月至当年8月;采用简单线性回归法建立植被指数与树轮宽度的拟合方程,重建历史时期高分辨率植被指数变化;因为观测数据仅有26年,所以采用逐一剔除方法[23]验证拟合方程的稳定性与可靠性,检验参数包括符号检验、乘积平均值和误差缩减值;取滑动步长L=3年、5年、10年、15年、20年、25年、30年、35年、40年、45年和50年,在0.05的显著性水平下,突变点出现次数较多（≥2次）的年份作为突变年份;采用功率谱方法[24]分析NDVI变化序列的周期特征。
1981-2006年月平均NDVI结果（图3）显示,1-3月NDVI没有明显变化,表明这段时间植被还未开始生长。4月NDVI值增加,说明植被开始萌芽返青,其后处于高速增加时期,7月达到全年最大值,表明此时植被是一年中最茂盛的时期。随后NDVI逐渐下降,表明植被开始陆续枯萎,生长开始停止。本文主要以植被生长季4-11月NDVI值作为研究对象。
3.2.1 树轮宽度与降水气温的相关关系 树轮宽度与降水量相关关系（图4a）表明,树轮宽度与前年9月、10月和当年7月降水的正相关均达到0.05置信水平。9月和10月树木径向生长已停止,但在此时气温条件下,光合作用仍持续进行,降水量多,有利于树木积累更多光合作用产物,以供给下年春季树木萌芽生长[25];且9月和10月降水增多,土壤能保留更多水分,有利于树木春季生长。生长季7月,降水增加,土壤水分含量及树木体内水分相应增加,有利于形成较宽年轮。
图4 树轮宽度、夏季NDVI与水热条件的相关系数（a. 树轮宽度与降水气温的相关,b. 树轮宽度与PDSI的相关,c. 夏季NDVI与降水气温的相关,d. 夏季NDVI与PDSI的相关;-6指前一年6月;**表示通过99%的置信水平;*表示通过95%的置信水平）
Fig. 4 Correlation coefficients between tree-ring width, summer NDVI and hydrothermal condition (a. correlation between tree-ring width and precipitation, temperature; b. tree-ring width and PDSI; c. summer NDVI and precipitation, temperature; d. summer NDVI and PDSI. Note: -6 refers to previous June, *P< 0.05, **P<0.01)
树轮宽度与气温相关关系（图4a）表明,树轮宽度与前一年8月、当年5月和7月气温负相关达到0.05显著水平。树轮宽度与前年8月气温显著负相关,可能由于树木生长的滞后效应造成。8月高温,树木消耗营养成分增加,所以体内剩余营养相对较少,对下年树木生长贡献相对较小,所以二者表现为负相关。树轮宽度与当年5月、7月温度显著负相关,说明生长季高温对树木径向生长的制约。树木生长季温度越高,蒸发作用和蒸腾作用越强烈,土壤及树木体内水分减少,光合作用效率降低,合成的营养物质减少;另外高温条件下呼吸作用强,消耗较多营养物质,因此树木体内营养物质相对减少,导致生长速率减缓,形成窄年轮[25]。可见树木年轮宽度与气温负相关的生理学意义是比较明确的。综上所述,树木径向生长受到降水和气温的明显制约。
3.2.2 树轮宽度与PDSI的相关关系 为研究降水和气温对树木径向生长的共同作用,选取PDSI与轮宽进行相关分析。结果（图4b）表明,树轮宽度与前一年9月至当年7月各月PDSI均显著正相关,且除6月为0.05显著水平外,其余各月均达到0.01显著水平。可见与降水气温相比,树轮宽度与PDSI显著相关月份明显增加,相关关系更加明显,说明树木径向生长受到水热条件的显著影响,对水热条件变化响应敏感。另外,分析树轮宽度与不同季节PDSI的相关关系。结果表明,轮宽与前年夏季、秋季、冬季、当年春季和夏季PDSI相关系数分别为0.067、0.641（P<0.001）、0.659（P<0.001）、0.706（P<0.001）、0.481（P<0.05）。
3.3.1 夏季NDVI与降水气温的相关关系 夏季NDVI与降水量相关结果（图4c）表明,夏季地表植被覆盖与当年3月、5月和7月降水的正相关均达到0.05的置信水平。3月降水多,土壤中储备水分多,植被返青时,水分供应较充足,所以植被长势相对较好,对夏季地表植被NDVI贡献大。5月和7月,植被处于生长旺季,此时降水多,满足植被生长需求,所以植被茂密,NDVI值相对高。
夏季NDV与气温相关关系（图4c）表明,与当年5月气温负相关达到0.01显著水平。5月植被正处于快速生长时期,此时气温高,蒸发作用和蒸腾作用消耗水分多,用于植被生长的水分减少,从而抑制生长速度,影响夏季地表植被覆盖程度。所以二者呈现负相关。
3.3.2 夏季NDVI与PDSI的相关关系 夏季NDVI与PDSI相关结果（图4d）表明,植被NDVI与前一年9月至当年7月各月PDSI正相关显著,且均达到0.01显著水平。
与降水气温相比,夏季NDVI与PDSI显著相关关系更加明显,地表植被覆盖受到降水和气温的共同影响。研究区植被NDVI对水热条件变化响应敏感。
综上所述,与水热条件的相关关系,夏季植被NDVI与树木径向生长基本一致,对外界水热变化的响应基本相似。树木径向生长与地表植被覆盖之间存在何种关系,将进一步探讨。
3.4.1 树轮宽度与NDVI的相关关系 为研究树轮宽度与植被指数变化是否存在一定共性,本文分析了树轮宽度与生长季4-11月NDVI的相关关系。
结果（表2）表明,树轮宽度与生长季植被NDVI多为正相关,尤其是RES年表与6-9月各月NDVI的相关关系都达到显著水平,与6月、7月和8月NDVI均达到0.01显著水平。进一步分析树轮宽度与6-9月和6-8月平均NDVI相关关系,发现RES年表与6-8月平均NDVI的相关系数最大（R=0.774,P<0.001）,达到0.01置信水平。
表2 树木年轮年表与NDVI的相关系数
Tab. 2 Correlation coefficients between tree-ring chronologies and NDVI
| 月份（组合） | XLSSTD | XLSRES |
|---|---|---|
| 4 | 0.208 | 0.178 |
| 5 | 0.380 | 0.373 |
| 6 | 0.501** | 0.604** |
| 7 | 0.572** | 0.697** |
| 8 | 0.445* | 0.613** |
| 9 | 0.243 | 0.406* |
| 10 | -0.151 | -0.034 |
| 11 | -0.117 | -0.060 |
| 6-9 | 0.631** | 0.768** |
| 6-8 | 0.643** | 0.774** |
树轮宽度是树木的年径向生长量,6-8月NDVI是一年中植被最茂盛时期的地表植被盖度状况,可见树轮宽窄变化与夏季NDVI的显著正相关是合理的,本研究区能够利用树轮宽窄变化反演历史时期的NDVI变化。
根据树轮宽度与植被指数的相关分析结果,并结合表1所列年表特征值,本文最终选用RES年表重建NDVI变化。
3.4.2 建立树轮宽度指数与夏季NDVI拟合方程选取当年轮宽指数（XLS）作为预报因子,重建夏季NDVI的拟合方程为：
此方程方差解释量为0.600,调整后的方差解释量0为.582,远超过0.001显著水平。F值34.472,超过0.001显著水平。重建NDVI与实测NDVI对比如图5所示。
图5 实测、重建NDVI和下年4-5月沙尘天气日数的对比
Fig. 5 Comparison between instrumental and reconstructed NDVI, and dust days in April-May of the following year
关于拟合方程的稳定性和重建序列的可靠性,采用逐一剔除检验法进行检验。检验参数包括符号检验、乘积平均值、误差缩减值和相关系数。结果（表3）表明重建值和实测值的原始值符号检验（S1）和一阶差符号检验（S2）分别通过了19个和16个,符号检验达到0.05显著性水平,说明重建序列与实测序列的低频变化趋势比较一致;乘积平均值为2.488,通过0.05显著水平,说明重建NDVI序列与实测NDVI序列比较接近;误差缩减值（RE）是精确检验估计气候重建值可靠性的统计量,本文中RE为0.534,说明重建结果可靠。以上结果说明拟合方程稳定,利用此方程重建研究区历史时期夏季NDVI变化是可行的。
表3 各项检验参数
Tab. 3 Verification statistics for the reconstruction model
| R | R2adj | F | S1 | S2 | t | RE |
|---|---|---|---|---|---|---|
| 0.774 | 0.582 | 34.472 | 19 (18, 20) | 16(18, 19) | 2.488 | 0.534 |
3.4.3 1845-2007年来夏季植被指数变化 子样本信号强度系数>0.85时,树轮年表有效区间为1845-2007年（表1）,采用拟合方程重建公元1845年来夏季NDVI变化（图6）。重建NDVI显示地表植被覆盖波动比较明显。1845-2007年NDVI平均值（mean）为0.40,标准差（
图6 公元1845年来夏季NDVI重建（a. NDVI,b. 兰州旱涝指数;比较细实线为年值,平滑曲线为5a滑动平均值）
Fig. 6 Summer NDVI reconstruction since 1845 AD (a) and comparison with the dryness/wetness index in Lanzhou (b)(The thin and solid lines represent yearly value and the smooth line represents the 5-year moving average)
5年NDVI滑动曲线显示,明显的高植被指数时期（多于4年）有1871-1877年、1884-1890年、1892-1896年、1933-1938年、1941-1950年、1956-1961年、1973-1979年、1985-1989年、1991-1997年和2002-2005年,说明植被生长相对良好,地表植被覆盖相对较高。明显的低植被指数时期有（多于4年）有1847-1850年、1855-1870年、1878-1883年、1897-1902年、1910-1916年、1921-1932年、1980-1984年和1998-2001年,说明植被生长状态较差,植被覆盖相对较低。
滑动t检验[26,27]表明NDVI年际变化在1870年、1871年、1872年、1873年、1899年、1900年、1931年、1932年、1933年、1934年、1935年和1936年发生过突变（表4）。研究区1899年、1900年和20世纪30年代的明显突变与亚洲季风在20世纪初、20-30年代发生的气候突变时间基本一致[26],植被覆盖受到季风变化影响。可见研究区生态环境演变,至少从公元1845年,不仅与周边地区具有一致性,而且受到更大范围气候变化影响。
表4 公元1845年来重建NDVI突变年份
Tab. 4 Abrupt-change years in NDVI reconstruction since 1845 AD
| 步长（年） | 突变年份 |
|---|---|
| 3 | 1863, 1867, 1870, 1873, 1886, 1889 |
| 5 | 1870, 1871, 1872 |
| 10 | 1870, 1871, 1933, 1935 |
| 15 | 1933, 1934, 1935 |
| 20 | 1870, 1871, 1872, 1931-1936 |
| 25 | 18701873, 1895, 1909, 1931-1935, 1941 |
| 30 | 1899-1903, 1930, 1932-1936 |
| 35 | 1898, 1899, 1900, 1906, 1931-1935 |
| 40 | 1935 |
| 45 | 1935 |
| 50 | - |
在干旱半干旱区,植被生长受到水热条件的明显制约。气候相对湿润,植被长势好,地表植被NDVI高;反之,气候干旱,则NDVI值偏低。本文对比了重建NDVI与《西北灾荒史》[28]中的旱灾记载。结果发现,重建NDVI明显低值期与旱灾发生基本对应（表5）,NDVI低值期与旱灾时期高度的一致性表明了重建NDVI序列能够指示研究区发生的旱灾。
表5 NDVI明显低值期与文献记载的旱灾
Tab. 5 Periods with low NDVI and droughts recorded in the literature
| NDVI低值期 | 西北灾荒史中的旱灾期 | 旱灾描述 |
|---|---|---|
| 1855-1870 | 1857-1871 | 西北地区共发生大旱7次,其间局部旱灾不断 |
| 1878-1883 | 1877-1884 | 西北发生毁灭性大旱,春夏不雨,赤地千里 |
| 1897-1902 | 1892-1909 | 西北地区或断或续发生大旱8次,其间局部旱灾几乎不断 |
| 1921-1932 | 1924-1933 | 西北地区大旱8年,其中1928-1930年三年为毁灭性大旱,为西北历史上成灾最重的大旱灾 |
本文中1998-2001年NDVI低值期,与腾格里沙漠和毛乌素沙地南2000-2001年低植被时期[29],与中国北方1999-2002年发生的严重且持续旱灾时期吻合[30],此阶段中国北方沙尘暴高发[29],且刚好和美国西部1999年左右旱灾[7]相一致。据此推测1998-2001年干旱可能是波及范围更广的气候事件。
为进一步验证重建NDVI序列的可靠性,对比分析重建NDVI与兰州旱涝指数[31,32]变化。旱涝指数序列依据历史文献记载和5-9月实测降水量评估某一地区湿润条件。采用1、2、3、4、5各等级分别代表等级：涝、偏涝、正常、偏旱和旱[32]。计算重建NDVI与旱涝指数（1845-2000年,除了1918-1922年）的长期相关,发现二者存在显著的负相关（R=-0.215,P<0.01）,即NDVI高值年对应于旱涝指数低值年,反之亦然。重建NDVI的年际变化趋势与研究区旱涝变化的基本一致性,从另一角度也证明重建序列的可靠。
研究区毗邻宁夏沙地,所以进一步探讨了树轮宽度与沙尘天气日数（扬沙+沙尘暴）的相关关系。发现树轮宽度与下年各月沙尘天气日数多表现负相关关系,其中与下年4月沙尘天气日数负相关达到显著水平（R=-0.395,P<0.05）,与下年4-5月总沙尘天气日数负相关显著（R=-0.436,P<0.05）,如图5所示,即树轮宽度窄,下年春季易出现沙尘天气。
相关研究表明,植被覆盖度是产生沙尘暴的阻力因子之一[33],二者呈现负相关[33,34],较低的植被覆盖是中国北方春季沙尘暴频发的一个重要影响因素[35],而且夏季地表植被覆盖影响下一年春季沙尘天气次数[34-36],原因是夏季植被残留根系的固沙作用、残留茎秆增加地表粗糙程度,增加地表摩擦力,对风动力强烈衰减[36]。所以重建夏季NDVI低值期一定程度上对应着下年春季4-5月沙尘天气的高发,1847-1850年、1855-1870年、1878-1883年、1897-1902年、1910-1916年、1921-1932年、1980-1984年和1998-2001年植被指数较低时期,沙尘天气可能增加。植被指数较高时期,沙尘天气减少,如1871-1877年、1884-1890年、1892-1896年、1933-1938年、1941-1950年、1956-1961年、1973-1979年、1985-1989年、1991-1997年和2002-2005年。
为研究重建序列与周边地区环境演变是否具有一致性,与祁连山区域6-8月NDVI[15]和德令哈地区6-9月NDVI[15,16]变化趋势进行对比。发现本文中NDVI变化明显的谷值时期（图7）,如1860-1865年,1878-1883年和1921-1932年,在祁连山和德令哈地区也表现为低NDVI,表明研究区生态环境演变与周边地区具有一定同步性。
图7 重建的1845-2007年NDVI10年滑动平均值与周边NDVI变化的对比（a. 研究区重建NDVI,b. 祁连山地区6-8月NDVI变化,c. 德令哈地区6-9月NDVI）
Fig. 7 Comparison between the 10-year moving average of NDVI reconstruction of the study area (a), June-August NDVI values in the Qilian Mountains (b) , and June-September NDVI in Delingha (c)
功率谱分析表明,公元1845年以来NDVI变化具有明显的2.45年（P<0.15）、2.51年（P<0.10）、2.57年（P<0.15）、2.63年（P<0.10）、3.09年（P<0.15）、4.91年（P<0.15）、5.14年（P<0.15）、13.5年（P<0.15）和15.43年（P<0.15）周期。
兴隆山树木径向生长与地表夏季植被NDVI,对于水热条件变化的响应,具有一致性。树轮宽度与夏季NDVI显著正相关（R=0.774,P<0.001,n=25）,所以利用树轮宽度重建了历史时期夏季NDVI变化。公元1845年来明显的NDVI低值期与文献记载的干旱时期基本对应,清晰指示了历史时期干旱,且重建的NDVI与旱涝指数呈显著负相关（n=151,R=-0.215,P<0.01）。
树轮宽度与下年多数月份沙尘天气日数呈现负相关关系,尤其与下年4月（P<0.05）沙尘天气日数成显著负相关,表明了树轮学研究古环境演变的巨大潜力。寻找长序列树轮资料,尤其是在沙漠地区或倾向于沙漠化地区,是全球变暖背景下古气候和古环境演变高分辨率研究的必然方向之一。
The authors have declared that no competing interests exist.
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Relationship between atmospheric CO2 variations and a satellite derived vegetation index. https://doi.org/10.1038/319195a0 URL [本文引用: 1] 摘要
Several schemes for correcting temperature and velocity measurements from moored current meters are tested on two moorings, one of which experienced large vertical excursions as the Gulf Stream meandered over it. The addition of two extra temperature recorders 100 m above and below the current meter permits the calculation of a reference corrected series through time dependent interpolation. By assuming that the current meter profiles the vertical temperature structure as it is pulled up and down it is possible to calculate the mean vertical temperature gradient and its dependence on temperature. A quadratic dependence is suggested by hydrographic measurements and the direct in situ measurements on the moorings. It is found possible, through weighted polynomial regression, to calculate this dependence directly from measurements of temperature and pressure on a single instrument and, thereby, to remove more than 95 percent of the mooring motion induced temperature variance. The correction of temperature for mooring motion is found necessary for accurate estimation of heat flux from moorings in energetic areas. Correction of velocity is more difficult but it is not found to have much effect on flux calculations.
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Increasing terrestrial vegetation activity in China, 1982-1999. https://doi.org/10.1007/BF03182768 URL PMID: 15524280 [本文引用: 2] 摘要
Variations in vegetation activity during the past 18 years in China were investigated using the normalized difference vegetation index (NDVI) derived from the 3rd generation time series dataset of NOAA-AVHRR from 1982 to 1999. In order to eliminate the effects of non-vegetation factors, we characterized areas with NDVI or = 0.1 as "vegetated areas". The results showed that increasing NDVI trends were evident, to varying extents, in almost all regions in China in the 18 years, indicating that vegetation activity has been rising in recent years in these regions. Compared to the early 1980s, the vegetated area increased by 3.5% by the late 1990s, while the sparsely vegetated area declined by 18.1% in the same period. The national total mean annual NDVI increased by 7.4% during the study period. Extended growing seasons and increased plant rates accounted for the bulk of these increases, while increases in temperature and summer rainfall, and strengthening agricultural activity were also likely important factors. NDVI changes in China exhibited relatively large spatial heterogeneity; the eastern coastal regions experienced declining or indiscernibly rising trends, while agricultural regions and western China experienced marked increases. Such a pattern was due primarily to urbanization, agricultural activity, regional climate characteristics, and different vegetation responses to regional climate changes.
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Spatio-temporal variations of vegetation cover on the Chinese Loess Plateau (1981-2006): Impacts of climate changes and human activities. https://doi.org/10.1007/s11430-007-0137-2 URL [本文引用: 1] 摘要
Spatiotemporal variations of Chinese Loess Plateau vegetation cover during 1981-2006 have been investigated using GIMMS and SPOT VGT NDVI data and the cause of vegetation cover changes has been analyzed, considering the climate changes and human activities. Vegetation cover changes on the Loess Plateau have experienced four stages as follows: (1) vegetation cover showed a continued increasing phase during 1981―1989; (2) vegetation cover changes came into a relative steady phase with small fluctuations during 1990―1998; (3) vegetation cover declined rapidly during 1999―2001; and (4) vegetation cover increased rapidly during 2002―2006. The vegetation cover changes of the Loess Plateau show a notable spatial difference. The vegetation cover has obviously increased in the Inner Mongolia and Ningxia plain along the Yellow River and the ecological rehabilitated region of Ordos Plateau, however the vegetation cover evidently decreased in the hilly and gully areas of Loess Plateau, Liupan Mountains region and the northern hillside of Qinling Mountains. The response of NDVI to climate changes varied with different vegetation types. NDVI of sandy land vegetation, grassland and cultivated land show a significant increasing trend, but forest shows a decreasing trend. The results obtained in this study show that the spatiotemporal variations of vegetation cover are the outcome of climate changes and human activities. Temperature is a control factor of the seasonal change of vegetation growth. The increased temperature makes soil drier and unfavors vegetation growth in summer, but it favors vegetation growth in spring and autumn because of a longer growing period. There is a significant correlation between vegetation cover and precipitation and thus, the change in precipitation is an important factor for vegetation variation. The improved agricultural production has resulted in an increase of NDVI in the farmland, and the implementation of large-scale vegetation construction has led to some beneficial effect in ecology.
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汉江流域NDVI与水热指数时空变化及相关性分析 .https://doi.org/10.11821/dlyj201309005 Magsci [本文引用: 1] 摘要
文章提出水热指数的概念和计算模型,运用经验正交函数和奇异值分解法对汉江流域1999-2010年的归一化植被指数及38个气象站点的气温和降水资料进行分析。结果表明:①汉江流域植被覆盖具有明显的空间差异,地形和农耕活动是最主要原因。②水热指数的空间分布也具有明显的规律,气温的纬度差异和雨带季节推移是根本原因;大地貌单元和季风气候是重要原因。其时间系数具有明显的冬夏差异,冬半年时间系数的绝对值及变率均较夏半年小,即水热组合冬半年差异小,夏半年差异大。③NDVI与水热指数之间呈现出高度正相关,但人类通过各种方式改变着地表覆盖和水热组合,使得两者之间的高度正相关在局部地区受到影响。
The correlation analysis and space-time changes of NDVI and hydro-thermal index in Hanjiang Basin. https://doi.org/10.11821/dlyj201309005 Magsci [本文引用: 1] 摘要
文章提出水热指数的概念和计算模型,运用经验正交函数和奇异值分解法对汉江流域1999-2010年的归一化植被指数及38个气象站点的气温和降水资料进行分析。结果表明:①汉江流域植被覆盖具有明显的空间差异,地形和农耕活动是最主要原因。②水热指数的空间分布也具有明显的规律,气温的纬度差异和雨带季节推移是根本原因;大地貌单元和季风气候是重要原因。其时间系数具有明显的冬夏差异,冬半年时间系数的绝对值及变率均较夏半年小,即水热组合冬半年差异小,夏半年差异大。③NDVI与水热指数之间呈现出高度正相关,但人类通过各种方式改变着地表覆盖和水热组合,使得两者之间的高度正相关在局部地区受到影响。
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Reassessing the evidence for tree-growth and inferred temperature change during the Common Era in Yamalia, northwest Siberia. https://doi.org/10.1016/j.quascirev.2013.04.008 URL Magsci [本文引用: 1] 摘要
The development of research into the history of tree growth and inferred summer temperature changes in Yamaha spanning the last 2000 years is reviewed. One focus is the evolving production of tree-ring width (TRW) and tree-ring maximum-latewood density (MXD) larch (Larix sibirica) chronologies, incorporating different applications of Regional Curve Standardisation (RCS). Another focus is the comparison of independent data representing past tree growth in adjacent Yamaha areas: Yamal and Polar Urals, and the examination of the evidence for common growth behaviour at different timescales. The sample data we use are far more numerous and cover a longer time-span at Yamal compared to the Polar Urals, but Yamal has only TRW, while there are both TRW and MXD for the Polar Urals. We use more data (sub-fossil and from living trees) than in previous dendroclimatic studies in this region. We develop a new TRW chronology for Yamal, more than 2000 years long and running up to 2005. For the Polar Urals we develop new TRW and MXD chronologies that show good agreement at short (<15 years) and medium (15-100 years) timescales demonstrating the validity of attempts to reconcile the evidence of longer-timescale information that they provide. We use a "conservative" application of the RCS approach (two-curve signal-free RCS), guarding against the possibility of "modern sample bias": a possible inflation of recent chronology values arising out of inadvertent selection of mostly relatively fast-growing trees in recent centuries. We also transform tree indices to have a normal distribution to remove the positive chronology skew often apparent in RCS TRW chronologies. This also reduces the apparent magnitude of 20th century tree-growth levels.<br/>There is generally good agreement between all chronologies as regards the major features of the decadal to centennial variability. Low tree-growth periods for which the inferred summer temperatures are approximately 2.5 degrees C below the 1961-90 reference are apparent in the 15-year smoothed reconstructions, centred around 1005, 1300, 1455, 1530, particularly the 1810s where the inferred cooling reaches -4 degrees C or even -6 degrees C for individual years, and the 1880s. These are superimposed on generally cool pre-20th century conditions: the long-term means of the pre-1900 reconstructed temperature anomalies range from -0.6 to -0.9 degrees C in our alternative reconstructions. There are numerous periods of one or two decades with relatively high growth (and inferred summer temperatures close to the 1961-1990 level) but at longer timescales only the 40-year period centred at 250 CE appears comparable with 20th century warmth. Although the central temperature estimate for this period is below that for the recent period, when we take into account the uncertainties we cannot be highly confident that recent warmth has exceeded the temperature of this earlier warm period. While there are clear warm decades either side of 1000 CE, neither TRW nor MXD data support the conclusion that temperatures were exceptionally high during medieval times. One previous version of the Polar Urals TRW chronology is shown here to be in error due to an injudicious application of RCS to non-homogeneous sample data, partly derived from root-collar samples that produce spuriously high chronology values in the 11th and 15th centuries. This biased chronology has been used in a number of recent studies aimed at reconstructing wider scale temperature histories. All of the chronologies we have produced here clearly show a generally high level of growth throughout their most recent 80 years. Allowing for chronology and reconstruction uncertainty, the mean of the last 100 years of the reconstruction is likely warmer than any century in the last 2000 years in this region. (C) 2013 The Authors. Published by Elsevier Ltd. All rights reserved.
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Asian monsoon failure and megadrought during the last millennium. URL PMID: 32873427810067930885292223222220413498332222225222101222228 [本文引用: 1] |
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Reconstruction of precipitation variation from tree rings in recent 1000 years in Delingha, Qinghai. https://doi.org/10.1360/03yd0146 URL 摘要
A major attempt of the studies on past global changes (PAGES) and climate variability and predict- ability (CLIVAR) is to reconstruct climate change us- ing high-resolution proxies[1―3]. Tree-ring data have played an important role in such studies. To d
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Moisture dipole over the Tibetan Plateau during the past five and a half centuries. https://doi.org/10.1038/ncomms9062 URL PMID: 26293214 摘要
The South Asian Monsoon and mid-latitude Westerlies are two important controls on Tibetan Plateau (TP) fresh water resources. Understanding their interaction requires long-term information on spatial patterns in moisture variability on the TP. Here we develop a network of 23 moisture-sensitive tree-ring chronologies from major juniper forests in a north-south transect on the eastern TP. Over the past five and a half centuries, we find that these chronologies cluster into two groups, North and South, of ~33 N. Southern and northern regional chronology subsets are positively and significantly correlated with May-June Palmer Drought Severity Indices (PDSI). The meridional moisture stress gradient reconstructed from these data suggests substantial stochastic variation, yet persistent moisture stress differences are observed between 1463-1502 CE and 1693-1734 CE. Identification of these patterns provides clues linking them with forced or intrinsic tropical-extratropical interactions and thus facilitates studies of interannual-decadal dipole variations in hydroclimate over the TP.
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Annual temperatures during the last 2485 years in the mid-eastern Tibetan Plateau inferred from tree rings. https://doi.org/10.1007/s11430-009-0025-z URL [本文引用: 1] 摘要
By combining living trees and archaeological wood, the annual mean temperatures were reconstructed based on ring-width indices of the mid-eastern Tibetan Plateau for the past 2485 years. The climate variations revealed by the reconstruction indicate that there were four periods to have average temperatures similar to or even higher than that mean of 1970 to 2000 AD. A particularly notable rapid shift from cold to warm, we call it the “Eastern Jin Event”, occurred from 348 AD to 413 AD. Calculation results show that the temperature variations over the mid-eastern Tibetan Plateau are not only representative for large parts of north-central China, but also closely correspond to those of the entire Northern Hemisphere over long time scales. During the last 2485 years, the downfall of most major dynasties in China coincides with intervals of low temperature. Compared with the temperature records in other regions of China during the last 1000 years, this reconstruction from the Tibetan Plateau shows a significant warming trend after the 1950s.
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The effect of growing season and summer greenness on northern forests. https://doi.org/10.1029/2004GL019608 URL [本文引用: 1] 摘要
[1] We investigate the physiological effects of the elongation of the growing season and the increase in summer greenness on northern hemisphere forests by examining the relationship between NDVI and tree rings. These variables are correlated during June and July only. These results suggest that NDVI proxies the physiological status of trees and that the summer status of the canopy has a larger effect on tree vigor than the duration of the canopy.
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High-latitude tree growth and satellite vegetation indices: Correlations and trends in Russia and Canada (1982-2008). https://doi.org/10.1029/2010JG001475 URL 摘要
Vegetation in northern high latitudes affects regional and global climate through energy partitioning and carbon storage. Spaceborne observations of vegetation, largely based on the normalized difference vegetation index (NDVI), suggest decreased productivity during recent decades in many regions of the Eurasian and North American boreal forests. To improve interpretation of NDVI trends over forest regions, we examined the relationship between NDVI from the advanced very high resolution radiometers and tree ring width measurements, a proxy of tree productivity. We collected tree core samples from spruce, pine, and larch at 22 sites in northeast Russia and northwest Canada. Annual growth rings were measured and used to generate site-level ring width index (RWI) chronologies. Correlation analysis was used to assess the association between RWI and summer NDVI from 1982 to 2008, while linear regression was used to examine trends in both measurements. The correlation between NDVI and RWI was highly variable across sites, though consistently positive (r = 0.43, SD = 0.19, n = 27). We observed significant temporal autocorrelation in both NDVI and RWI measurements at sites with evergreen conifers (spruce and pine), though weak autocorrelation at sites with deciduous conifers (larch). No sites exhibited a positive trend in both NDVI and RWI, although five sites showed negative trends in both measurements. While there are technological and physiological limitations to this approach, these findings demonstrate a positive association between NDVI and tree ring measurements, as well as the importance of considering lagged effects when modeling vegetation productivity using satellite data.
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Variations in Anarthrophyllum rigidum radial growth, NDVI and ecosystem productivity in the Patagonian shrubby steppes. https://doi.org/10.1007/s11258-011-9955-6 Magsci 摘要
The lack of long-term records of productivity is a critical limitation to the study of ecosystem dynamics. Annual rings, a measure of growth in woody species, are a useful tool to document ecosystem dynamics. Time series of the Normalized Difference Vegetation Index (NDVI) provide estimates of ecosystem productivity through satellite-derived data on the fraction of photosynthetic active radiation absorbed by vegetation. In the Patagonian steppes, we relate changes in NDVI to interannual variations in the radial growth of the shrub Anarthrophyllum rigidum. A widely distributed network of 15 ring-width chronologies of A. rigidum was used to estimate changes in NDVI across the Patagonia steppe (35A degrees-50A degrees S). In most sites, interannual variations in shrub growth and NDVI are regulated by winter precipitation. The water accumulated in the soil during winter is used by A. rigidum during the growing season, concurrent with the maximum NDVI values. At 10 from the 15 selected sites, variations in the radial growth of A. rigidum explained between 23 and 62% of the total variance in seasonal NDVI, suggesting that the A. rigidum growth at some sites provides good estimates of productivity in the Patagonian shrubby steppes during the growing season. However, we were unable to determine clear relationships between radial growth and NDVI at high-elevation mountainous sites or where intensive grazing by sheep masked the effect of climate variability on shrub growth. We conclude that dendrochronological methods can complement other estimates to reconstruct variations of productivity, supplementing and extending the few short records available in the Patagonian steppe.
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| [14] |
Assessing the recent grassland greening trend in a long-term context based on tree-ring analysis: A case study in North China. https://doi.org/10.1016/j.ecolind.2009.02.007 URL 摘要
Records of the Normalized Difference Vegetation Index (NDVI) and of the productivity of grassland are not long enough to reliably capture natural variation of the grassland dynamics. Herein, we compared a 20-year long growing-season NDVI time series of a typical steppe in North China, and the first principal component (PC1) of four tree-ring width chronologies (based on 69 trees from 3 Pinus tabulaeformis sites and 1 Picea meyeri site) with climate data. Both variables are significantly correlated to each other and to April-uly rainfall as well as relative air humidity. This is why PC1 was taken as an indicator of greenness of vegetation in a typical steppe since 1850. The recent greening trend may have happened several times in the past as part of the moisture-driven natural variability. Periods of low growing-season NDVI values derived from tree rings were validated by historical documents. In spite of the ecological complexity, tree-ring analysis provides a simple and efficient method to mirror the key characteristics of the underlying ecological process that was primarily controlled by moisture availability. Thus, tree-ring width time series, clearly documenting the signals of environmental influences, conveys invaluable information about the steppe greenness dynamics and enables us to put the recent greening trend in a long-term context.
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| [15] |
基于祁连山树轮宽度指数的区域NDVI重建 .https://doi.org/10.3773/j.issn.1005-264x.2010.09.004 Magsci [本文引用: 2] 摘要
利用祁连山自东向西5条树轮宽度年表序列和1986–2003年间的归一化植被指数(<em>NDVI</em>),分析了<em>NDVI</em>的时空变化及其与树轮宽度年表之间的关联。结果表明, 祁连山地区植被的生长主要集中在6–8月。空间上,<em> NDVI</em>值从祁连山东段向西段逐渐减小; 在1986–2003时段内, 东、中和西段生长季的<em>NDVI</em>值分别增长了3.28%、4.82%和7.75%。整个祁连山地区的<em>NDVI</em>变化与5个宽度年表的第一主成分相关性较高(<em>r</em> = 0.74,<em> p</em> < 0.01)。基于此, 利用树轮宽度RES年表的第一主成分重建了1843–2003年间祁连山地区生长季的<em>NDVI</em>变化曲线。重建的<em>NDVI</em>曲线表现出6个高值期和6个低值期, 其中1923–1932的10年间植被生长状况最差。另外, 在1989–2003时段内<em>NDVI</em>年际波动较大, 总体上表现为<em>NDVI</em>低于平均值, 但是从1991年开始, <em>NDVI</em>有上升的趋势。
Reconstruction of regional NDVI using tree-ring width chronologies in the Qilian Mountains, Northwestern China. https://doi.org/10.3773/j.issn.1005-264x.2010.09.004 Magsci [本文引用: 2] 摘要
利用祁连山自东向西5条树轮宽度年表序列和1986–2003年间的归一化植被指数(<em>NDVI</em>),分析了<em>NDVI</em>的时空变化及其与树轮宽度年表之间的关联。结果表明, 祁连山地区植被的生长主要集中在6–8月。空间上,<em> NDVI</em>值从祁连山东段向西段逐渐减小; 在1986–2003时段内, 东、中和西段生长季的<em>NDVI</em>值分别增长了3.28%、4.82%和7.75%。整个祁连山地区的<em>NDVI</em>变化与5个宽度年表的第一主成分相关性较高(<em>r</em> = 0.74,<em> p</em> < 0.01)。基于此, 利用树轮宽度RES年表的第一主成分重建了1843–2003年间祁连山地区生长季的<em>NDVI</em>变化曲线。重建的<em>NDVI</em>曲线表现出6个高值期和6个低值期, 其中1923–1932的10年间植被生长状况最差。另外, 在1989–2003时段内<em>NDVI</em>年际波动较大, 总体上表现为<em>NDVI</em>低于平均值, 但是从1991年开始, <em>NDVI</em>有上升的趋势。
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| [16] |
Relationships between tree-ring width index and NDVI of grassland in Delingha. https://doi.org/10.1007/s11434-006-1106-4 Magsci [本文引用: 2] |
| [17] |
Relationship between masson pine tree-ring width and NDVI in North Subtropical Region. https://doi.org/10.2307/41604471 URL [本文引用: 1] 摘要
North Subtropical Area of China,located in the transition from warm temperate zone to the subtropical,is more sensitive to environmental changes.Therefore,study on the relationship between masson pine(Pinus Massoniana) tree-ring width data and NDVI in north subtropical region where masson pine growth is more sensitive to changes of climatic factors,is of much importance to reveal how the terrestrial ecosystems respond to global climate change. As the northern boundary of masson pine natural distribution,Nanzheng county of Shanxi Province and Jigongshan National Nature Reserve of Henan Province were selected.Using masson pine tree-ring width indices,monthly normalized difference vegetation index(NDVI) and climatic data from 1982 to 2006,the relationships between tree-ring width indices,NDVI,and climatic data,including monthly mean temperature,precipitation and the Palmer Drought Severity Index(PDSI) were analyzed firstly.Then,the relationship between tree-ring width indices and NDVI of forest was explored.The results showed that North Subtropical vegetation index NDVI was influenced by the hydrothermal conditions,and monthly NDVI was mainly positive to monthly mean temperature,negatively related to monthly mean precipitation and PDSI.In addition,the correlation coefficient between NDVI and temperature was larger than other factors.Masson pine radial growth was positive to temperature of last growing season,while negative to precipitation and PDSI.Temperature and precipitation during the growing season of the same year promoted the pine radial growth,the influences of PDSI on Nanzheng county and Jigognshan were opposite.In northern subtropical region,the relationship between masson pine tree-ring width and forest NDVI was not significant(P0.05).However,NDVI of Nanzheng County in March,August and December were significantly associated with two chronologies,NDVI of Jigongshan region in September associated with the RES chronology with the biggest correlation coefficient.Through analyzing synthetically,we figure out that the tree growth of Nanzheng county was mainly affected by temperature,that of Jigongshan was influenced by the interaction of temperature and precipitation.In conclusion,we imply that long time series of ring width data does not reflect well the long-term vegetation changes in the northern subtropical region,and it is unreasonable to model and reconstruct the long-term vegetation changes and productivity using tree radial growth.Therefore,the further study is still required to reconstruct regional NDVI using tree-ring width chronologies in the North Subtropical Region.
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| [18] |
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| [19] |
Drought variations in the eastern part of Northwest China over the past two centuries: evidence from tree rings. https://doi.org/10.3354/cr00781 URL [本文引用: 1] 摘要
Drought reconstruction from 1794 to 2003 in the eastern part of NW China was developed by calibrating tree rings of Picea wilsonii on Xinglong Mountain with the Palmer drought severity index (PDSI). The reconstruction explains 40% of the actual PDSI variance during the period from 1951 to 2003. The most significant drought period over the reconstructed time span occurred during the 1920s to 1930s. The drought reconstructions show a climate transition in 1921 on a decadal scale and significant cyclic patterns that were identified in intervals of 10.5, 7.9-8.3, -3.5, 3.0-3.2, 2.7-2.8 and -2 yr. This reconstruction is representative of regional drought patterns in eastern NW China and demonstrates that they are different from patterns in western NW China. Inter-Research 2009.
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Computer-assisted quality control in tree-ring dating and measurement. Tree-ring https://doi.org/10.1006/biol.1999.0214 URL [本文引用: 1] 摘要
Abstract This study surveyed strategies of sequencing primer selection and evaluated primer performance in automated DNA sequencing. We asked participants to relate their preferred primer design strategies to identify primer characteristics that are considered most important in sequencing primer design. The participants preferred primers of 18-24 nucleotides (nt), 39%-58% G + C, a melting temperature (Tm) of 53 degrees-65 degrees C with a 1-2 nt 3' GC clamp, hairpin stems of less than 2-3 bp, homopolymeric runs of less than 4-5 nt, primer dimers of less than 3-4 bp and secondary priming sites of less than 3-4 bp. We provided a 300-bp test sequence and asked participants to submit sequences of 1-3 optimal sequencing primers. Submitted primers ranged from 17-24 nt and largely conformed to the preferred parameters. Submitted primers were distributed across the test sequence, although some sites were disfavored. Surprisingly, approximately 45% of the primers were selected "manually", more than by any software package. Each of 69 submitted and 95 control primers, distributed at 3-bp intervals across the test sequence, were synthesized, purified and tested using a Model 377 PRISM DNA Sequencer with dichlororhodamine dye terminator reagents (dRhodamine dye terminators). Approximately half of the control primers were also tested using rhodamine dye terminator reagents ("old" rhodamine dye terminators). The results indicated that primer physico-chemical characteristics thought to have a strong impact on sequencing performance had surprisingly little effect. Thus, primers with high or low percent G + C or Tm, strong secondary priming scores or long 3' homopolymeric stretches yielded excellent sequences with the dRhodamine dye terminator reagents, although these characteristics had a stronger effect when the old rhodamine reagents were used. The old rhodamine reagents gave sequences with a similar average read length, but the number of errors and ambiguities or "N's" was consistently higher. Moreover, the effects of the primer physico-chemical characteristics were also more evident with the old rhodamine dyes. We conclude that under optimal sequencing conditions with highly pure template and primer, many of the commonly applied primer design parameters are dispensable, particularly when using one of the new generation of sequencing reagents such as the dichlororhodamine dye terminators.
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| [21] |
Users Manual for Program ARSTAN. Tucson, USA: Laboratory of Tree-ring Research, https://doi.org/10.2172/138036 URL [本文引用: 1] 摘要
This report describes how to use a revised version of the ORIGEN computer code, designated ORIGEN2. Included are a description of the input data, input deck organization, and sample input and output. ORIGEN2 can be obtained from the Radiation Shielding Information Center at ORNL.
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| [22] |
On the average value of the correlated time series, with applications in dendroclimatology and hydrometeorology. |
| [23] |
Cross-validation in statistical climate forecast models. |
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| [25] |
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| [26] |
南亚夏季风长期变化中的突变现象及其与全球迅速增暖的同步性 .https://doi.org/10.1007/BF02919267 URL [本文引用: 2] 摘要
本文分析了1888年以来南亚 夏季风活动长期变化的主要特点,用Mann-KendallRank Statistic方法检测到本世纪20年代夏季风活动突然增强的季风气候突变现象,并且发现这一突变现象与该时期全球迅速增暖几乎是同时的,对突变时期 季风区环流和海陆热状况的诊断表明,北半球增暖期间陆地增暖明显大于、早于海洋,陆地和海洋热力差异迅速加大,促使季风低压发展,季风气流中的扰动加强, 是夏季风突然增强的一个直接原因.
The abrupt change phenomena of the southern Asia monsoon secular variation and its synchronization with global warming. https://doi.org/10.1007/BF02919267 URL [本文引用: 2] 摘要
本文分析了1888年以来南亚 夏季风活动长期变化的主要特点,用Mann-KendallRank Statistic方法检测到本世纪20年代夏季风活动突然增强的季风气候突变现象,并且发现这一突变现象与该时期全球迅速增暖几乎是同时的,对突变时期 季风区环流和海陆热状况的诊断表明,北半球增暖期间陆地增暖明显大于、早于海洋,陆地和海洋热力差异迅速加大,促使季风低压发展,季风气流中的扰动加强, 是夏季风突然增强的一个直接原因.
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| [27] |
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| [28] |
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| [29] |
基于遥感的贺兰山两侧沙漠边缘带植被覆盖演变及对气候响应 .https://doi.org/10.3321/j.issn:1000-6060.2006.02.002 URL [本文引用: 2] 摘要
使用NOAA/AVHRR 8KM 1981-2001数据,以及准同期逐日观测气象数据,用GIS与RS空间分析方法和数理统计的分析方法对数据进行了归纳和插值处理.对贺兰山东西两侧腾 格里与毛乌素两大沙漠的南缘带植被覆盖、气候要素的降水与气温变化特征以及它们之间的响应关系进行了分析.通过比较得出不同干湿条件沙漠边缘带植被覆盖状 态变化的差异,以及各自生境对气候变化的响应特征.研究表明:气候条件中水分条件是决定干旱区与半干旱区土地覆盖状态的关键性因素;但是地形条件对植被覆 盖的季相差异的影响也不可忽视;与植被覆盖相比,低覆盖植被分布面积的变化可以更好的揭示生态环境对气候变化的响应;整个研究期气候整体趋于暖干化,暖干 程度在1999-2000年达到了高峰,随之植被覆盖在2000-2001年达到了最低值.这说明生态环境对气候变化的响应存在一种时间上的滞后性.从 RS与GIS角度为干旱区与半干旱区沙漠边缘带宏观土地覆盖变化研究提供了一种较为可靠方法,为因地制宜进行生态环境综合治理与防治土地沙漠化也提供一种 新的参考.
RS-based study on the change of vegetation cover and its response to climate change in two desert marginal zones at both sides of the Helan Mountain. https://doi.org/10.3321/j.issn:1000-6060.2006.02.002 URL [本文引用: 2] 摘要
使用NOAA/AVHRR 8KM 1981-2001数据,以及准同期逐日观测气象数据,用GIS与RS空间分析方法和数理统计的分析方法对数据进行了归纳和插值处理.对贺兰山东西两侧腾 格里与毛乌素两大沙漠的南缘带植被覆盖、气候要素的降水与气温变化特征以及它们之间的响应关系进行了分析.通过比较得出不同干湿条件沙漠边缘带植被覆盖状 态变化的差异,以及各自生境对气候变化的响应特征.研究表明:气候条件中水分条件是决定干旱区与半干旱区土地覆盖状态的关键性因素;但是地形条件对植被覆 盖的季相差异的影响也不可忽视;与植被覆盖相比,低覆盖植被分布面积的变化可以更好的揭示生态环境对气候变化的响应;整个研究期气候整体趋于暖干化,暖干 程度在1999-2000年达到了高峰,随之植被覆盖在2000-2001年达到了最低值.这说明生态环境对气候变化的响应存在一种时间上的滞后性.从 RS与GIS角度为干旱区与半干旱区沙漠边缘带宏观土地覆盖变化研究提供了一种较为可靠方法,为因地制宜进行生态环境综合治理与防治土地沙漠化也提供一种 新的参考.
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我国旱涝气候灾害的年代际变化及其与东亚气候系统变化的关系 .
通过观测资料分析我国旱涝灾害的年代际变化特征，表明从1976年之后迄今我国华北地区发生持续干旱，严重影响了此地区的水资源和经济的可持续发展，并且长江、淮河流域夏季季风降水明显增加，洪涝灾害频繁发生。作者还从东亚气候系统的年代际变化系统地分析了发生在我国旱涝气候灾害年代际变化的机理。分析结果表明：从20世纪70年代中后期迄今，热带中、东太平洋海温上升，并出现“类似于厄尔尼诺（El Nino）型”分布的年代际海温距平。这不仅引起了东亚和西太平洋上空EAP型遥相关环流异常分布的年代际变化，使得从1976年之后迄今东亚夏季风变弱、西太平洋副热带高压偏南、偏西，而且引起了热带Walker环流的变化；并且，由于热带Walker环流的年代际变化，引起了从20世纪70年代中后期到现在北非上空下沉气流的加强，从而使得萨赫勒及以东地区上空反气旋环流异常增强，并由于遥相关波列的传播，从而导致我国华南上空反气旋环流距平的增强；此外，中高纬度欧亚型遥相关环流异常分布也发生了年代际变化，使得1976年之后我国华北地区上空出现反气旋环流异常。这些使得到达华北的偏南季风气流减弱和长江、淮河流域水汽输送的辐合，从而导致了我国旱涝的年代际变化。分析结果还表明了从20世纪70年代后期迄今青藏高原冬、春积雪天数增多，深度加深，以及我国西北干旱、半干旱区地-气温差增大，这些有利于长江和淮河流域夏季降水增多，而不利于华北地区夏季降水。
Interdecaldal variations of drought and flooding disasters in China and their association with the East Asian climate system.
通过观测资料分析我国旱涝灾害的年代际变化特征，表明从1976年之后迄今我国华北地区发生持续干旱，严重影响了此地区的水资源和经济的可持续发展，并且长江、淮河流域夏季季风降水明显增加，洪涝灾害频繁发生。作者还从东亚气候系统的年代际变化系统地分析了发生在我国旱涝气候灾害年代际变化的机理。分析结果表明：从20世纪70年代中后期迄今，热带中、东太平洋海温上升，并出现“类似于厄尔尼诺（El Nino）型”分布的年代际海温距平。这不仅引起了东亚和西太平洋上空EAP型遥相关环流异常分布的年代际变化，使得从1976年之后迄今东亚夏季风变弱、西太平洋副热带高压偏南、偏西，而且引起了热带Walker环流的变化；并且，由于热带Walker环流的年代际变化，引起了从20世纪70年代中后期到现在北非上空下沉气流的加强，从而使得萨赫勒及以东地区上空反气旋环流异常增强，并由于遥相关波列的传播，从而导致我国华南上空反气旋环流距平的增强；此外，中高纬度欧亚型遥相关环流异常分布也发生了年代际变化，使得1976年之后我国华北地区上空出现反气旋环流异常。这些使得到达华北的偏南季风气流减弱和长江、淮河流域水汽输送的辐合，从而导致了我国旱涝的年代际变化。分析结果还表明了从20世纪70年代后期迄今青藏高原冬、春积雪天数增多，深度加深，以及我国西北干旱、半干旱区地-气温差增大，这些有利于长江和淮河流域夏季降水增多，而不利于华北地区夏季降水。
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| [31] |
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《中国近五百年旱涝分布图集》的再续补(1993-2000年) .https://doi.org/10.3969/j.issn.1001-7313.2003.03.015 URL [本文引用: 2] 摘要
由中国气象科学研究院主编,全国32家单位协作完成的<中国近五百年旱涝分布图集>[1](以下简称<图集>)已被国内、外学者 广泛地用于科学研究和实际业务诸多方面.该<图集>的资料截止于1979年,其1980～1992年的序列资料和逐年分布图已作了续补 [2].现对1993～2000年时段作再续补.
Re-continuation (1993-2000) of the "Yearly Charts of Dryness/Wetness in China for the Last 500 Years Period". Journal of Applied. https://doi.org/10.3969/j.issn.1001-7313.2003.03.015 URL [本文引用: 2] 摘要
由中国气象科学研究院主编,全国32家单位协作完成的<中国近五百年旱涝分布图集>[1](以下简称<图集>)已被国内、外学者 广泛地用于科学研究和实际业务诸多方面.该<图集>的资料截止于1979年,其1980～1992年的序列资料和逐年分布图已作了续补 [2].现对1993～2000年时段作再续补.
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中国北方沙尘灾害影响因子分析 .
<p>利用中国北方1951—2000年188个沙尘暴代表站的气象观测数据和1983—2000年EROS数据中心NDVI数据，对我国北方沙尘灾害的影响因子进行了分析。主要结论有：①在影响沙尘暴发生、发展、演化的自然因子中，植被覆盖度、降水、大风日数和温度起关键作用，夏季植被覆盖度对来年春季沙尘暴发生频次影响较大，降水和温度主要表现在对地表植被覆盖等与沙尘暴有关的地表参数的影响；②大风日数和温度是沙尘暴形成的动力因子，植被覆盖度和降水是阻力因子。沙尘暴日数和持续时间的变化，主要取决于动力因子与阻力因子的综合作用；③遏制沙尘灾害的治本办法，不在于治理沙尘暴本身，而在于消除产生土地退化、生态安全下降的社会原因，处理好发展与生态环境建设的关系。</p>
The impact factor analysis of dust storm disaster in northern China.
<p>利用中国北方1951—2000年188个沙尘暴代表站的气象观测数据和1983—2000年EROS数据中心NDVI数据，对我国北方沙尘灾害的影响因子进行了分析。主要结论有：①在影响沙尘暴发生、发展、演化的自然因子中，植被覆盖度、降水、大风日数和温度起关键作用，夏季植被覆盖度对来年春季沙尘暴发生频次影响较大，降水和温度主要表现在对地表植被覆盖等与沙尘暴有关的地表参数的影响；②大风日数和温度是沙尘暴形成的动力因子，植被覆盖度和降水是阻力因子。沙尘暴日数和持续时间的变化，主要取决于动力因子与阻力因子的综合作用；③遏制沙尘灾害的治本办法，不在于治理沙尘暴本身，而在于消除产生土地退化、生态安全下降的社会原因，处理好发展与生态环境建设的关系。</p>
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| [34] |
植被覆盖与沙尘暴日数分布关系的探讨: 以内蒙古中西部地区为例 .
<p>利用NOAA/AVHRR的NDVI数据和地面气象观测数据，以植被覆盖率和年沙尘暴日数为指标，分析了内蒙古中西部地区植被覆盖与沙尘暴分布的关系。研究结果表明，在内蒙古中西部地区，80年代沙尘暴日数的正距平与植被覆盖率的负距平、90年代沙尘暴日数的负距平与植被覆盖率的正距平是相互对应的；沙尘暴日数与植被覆盖率之间呈现负的相关关系，这种相关关系在不同地貌类型区和不同季节有所差异；沙地区的夏季（7、8、9月平均）植被覆盖率与第 2年沙尘暴日数之间的负相关最为显著。</p>
Study on relationship between vegetation cover and distribution days of sandstorm-taking central and western Inner Mongolia for example.
<p>利用NOAA/AVHRR的NDVI数据和地面气象观测数据，以植被覆盖率和年沙尘暴日数为指标，分析了内蒙古中西部地区植被覆盖与沙尘暴分布的关系。研究结果表明，在内蒙古中西部地区，80年代沙尘暴日数的正距平与植被覆盖率的负距平、90年代沙尘暴日数的负距平与植被覆盖率的正距平是相互对应的；沙尘暴日数与植被覆盖率之间呈现负的相关关系，这种相关关系在不同地貌类型区和不同季节有所差异；沙地区的夏季（7、8、9月平均）植被覆盖率与第 2年沙尘暴日数之间的负相关最为显著。</p>
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| [35] |
Relationship between vegetation coverage and spring dust storms over northern China. https://doi.org/10.1029/2003JD003913 URL [本文引用: 1] 摘要
Abstract Top of page Abstract 1.Introduction 2.Data Source and Methods 3.Vegetation Control on Spring Dust Storms 4.Relationship Between Variation of Vegetation and Spring Dust Storms 5.Conclusions Acknowledgments References Supporting Information [1] On the basis of normalized difference vegetation index (NDVI) data from 1982 to 2001 and dust storm observations in China the relationship between vegetation and spring dust storms over northern China is discussed. The results show that poor vegetation coverage in northern China is one important factor for the frequent occurrence of spring dust storms. In addition, vegetation cover plays an important role in interannual variations of dust storms. In general, a negative correlation is noted between vegetation coverage and occurrence of dust storms in northern China for spring during the period 1982-2001. The correlation coefficient between vegetation coverage and areas affected by dust storms is 0.59, which is statistically meaningful at 99% confidence level. The sharp decrease of spring vegetation coverage in recent years is one of the major contributors to frequent spring dust storms over northern China specifically during 2000 and 2001. A negative correlation is especially significant in the eastern part of northern China, mainly in central and eastern Inner Mongolia. When vegetation decreases (increases), the occurrence of dust storms increases (decreases). Furthermore, statistics show that abundant vegetation in previous seasons could help reduce dust storms in the coming spring. The effect of prior summer vegetation on the variation of spring dust storms is particularly evident in the central and eastern part of northern China. Because of the presence of little to no vegetation in the desert areas of northwest China the variation in occurrence of spring dust storms seems unrelated to the vegetation.
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| [36] |
植被覆盖对沙尘天气滞后性影响的机制分析 .
1982～2000年卫星和335个气象台站沙尘天气观测资料相 关分析显示,中国区域沙尘天气年发生频次与植被覆盖率存在非线性关系.在沙尘天气主要发生源地,夏季植被的覆盖状况会直接影响后期冬春两季各类沙尘天气的 发生次数,而这种影响机制却不清楚.本研究通过准地转正压模式,从3个摩擦量级分析了上述现象的物理机制.结果表明,在大气与水面摩擦系数量级,最高可在 72 h内使边界层大气风速平均下降90%;在大气与裸土摩擦量级,18 h内边界层大气平均风速最高可下降100%;在大气与植被摩擦量级,1 h内边界层大气平均风速就可以下降100%.观测事实和模拟结果证实,地表植被残存的根茎,是影响冬春两季沙尘天气发生频次的重要因素之一.残留根茎对大 气的摩擦阻挡作用,是夏季植被对沙尘天气产生滞后性作用的主要机制.
Process study on hysteresis of vegetation cover influencing sand-dust events.
1982～2000年卫星和335个气象台站沙尘天气观测资料相 关分析显示,中国区域沙尘天气年发生频次与植被覆盖率存在非线性关系.在沙尘天气主要发生源地,夏季植被的覆盖状况会直接影响后期冬春两季各类沙尘天气的 发生次数,而这种影响机制却不清楚.本研究通过准地转正压模式,从3个摩擦量级分析了上述现象的物理机制.结果表明,在大气与水面摩擦系数量级,最高可在 72 h内使边界层大气风速平均下降90%;在大气与裸土摩擦量级,18 h内边界层大气平均风速最高可下降100%;在大气与植被摩擦量级,1 h内边界层大气平均风速就可以下降100%.观测事实和模拟结果证实,地表植被残存的根茎,是影响冬春两季沙尘天气发生频次的重要因素之一.残留根茎对大 气的摩擦阻挡作用,是夏季植被对沙尘天气产生滞后性作用的主要机制.
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