基于SPOT NDVI的阿尔金山自然保护区植被动态变化研究

气候变化对陆地生态系统,特别是高寒地区植被的影响是全球变化研究的重要方面。利用1998-2008年SPOT VGT [WTBX]NDVI[WTBZ]植被指数,分析了阿尔金山[WTBX]NDVI[WTBZ]时空变化特征及其与主要气候因子(气温、降水)的相关关系。结果表明：保护区平均[WTBX]NDVI[WTBX]年内季节变化明显,[WTBX]DN[WTBZ]变化幅度在33~53,5月开始较快上升,最高值出现在9月,其多年平均值为40,总体上呈先下降后上升的趋势。从空间分布上看,[WTBX]NDVI[WTBZ]的高值主要集中在阿雅克湖流域,特别是卡尔敦检查站附近。趋势分析表明,除河流、湖泊附近的植被有所退化外,保护区内部植被总体上有所改善,气温和降水与[WTBX]NDVI[WTBZ]线性相关显著;而保护区边缘植被有不同程度的退化,人类活动或许是植被退化的诱导因素。     

新疆伊犁河流域植被变化动态监测与评价

基于2000-2013年MODIS/NDVI数据和研究区内气象站点资料,分析了伊犁河流域植被生长季NDVI时空变化特征及其与气候因子的关系。结果表明:1)研究区植被整体呈微弱的退化趋势,年退缩率为-0.8×10-3a-1,其中草原的退化趋势较草甸、灌丛和林地略显著。2)2000-2013年研究区植被退化区面积占研究区总面积的11.45%,主要分布在特克斯河中下游、巩乃斯河周边地区;植被改善面积占全区总面积的8.38%,主要分布在伊宁市及霍尔果斯河周边地区。3)研究区伊宁站周边植被生长季NDVI与同期气温及降水存在不显著相关性,昭苏站周边植被生长季NDVI与同期气温及降水分别存在显著负相关和极显著正相关。气候的暖干化趋势可能是导致伊犁河流域植被生长退化的主要原因。     

基于MODIS/NDVI的塔里木河流域植被覆盖变化驱动因素相对作用分析

塔里木河流域是我国生态较为脆弱的地区,过去几十年不合理的开发,导致植被覆盖遭到严重破坏。2001年以后,随着"塔里木河流域近期综合治理项目"等系列生态工程的实施,流域环境得到初步改善,植被覆盖日益好转。利用2001—2013年逐旬MODIS/NDVI数据和气象数据,通过分离气候变化对塔里木河流域植被覆盖的影响,对气候变化和人类活动对植被覆盖变化的相对作用进行定量分析。研究表明:(1)2001—2013年塔里木河流域植被覆盖总体呈增长趋势;植被覆盖呈改善趋势的区域占流域总面积的28.02%,呈退化趋势的区域占10.99%,其他区域则基本不变。(2)采用相关分析与残差法分析了气候变化和人类活动对植被覆盖变化的影响,结果表明植被覆盖变化与气候因子显著相关;人类活动对植被覆盖变化起积极作用的面积占流域总面积的61.8%,起消极作用的占38.2%。(3)通过对植被覆盖变化驱动因素进行相对作用分析,可以得出在植被改善区和植被退化区,人类活动的作用相对于气候因素更大,是植被覆盖变化的主要驱动因素。     

基于GIMMS NDVI的中亚干旱区植被覆盖时空变化

选用1982—2013年GIMMS NDVI数据,运用变异系数法、Theil-Sen median趋势分析耦合Mann-Kendall检验以及Hurst指数法,研究了中亚干旱区植被覆盖的空间格局、不同维度的空间变异性、时间变化特征和未来趋势预测。同时,结合CRU降水、气温资料和MODIS土地覆盖数据,对植被覆盖时空格局及其变化的驱动因素进行分析。结果表明:1 1982—2013年中亚干旱区植被覆盖有较强的空间异质性,有植被覆盖的区域占总面积的85.32%,无植被覆盖的区域占14.68%。受降水量控制,植被覆盖呈山区高平原低、西部高东部低、北部高南部低的特点;受河流和人工灌溉的影响,绿洲区的植被覆盖高于荒漠区。2近32 a全区植被覆盖的波动变化较明显,各变异程度的面积比例:中等波动变化相对较高的波动变化高波动变化相对较低的波动变化低波动变化。受降水变率和人工种植的影响,植被覆盖的高波动变化主要在荒漠区和诸流域绿洲区;低波动变化主要在植被生长良好的区域。3 32 a间全区NDVI呈增长趋势,NDVI距平的变化率为0.01·(10a)~(-1)。基于像元尺度的分析也表明,全区植被覆盖变化趋势以增加为主,各类变化趋势的面积比例:轻微增加显著增加轻微减小显著减小无法确定。植被改善是区域气候增湿增暖和绿洲土地覆盖变迁所致。4全区NDVI的Hurst指数均值为0.63,Hurst指数大于0.5的范围所占比例为75.17%,即未来全区植被覆盖的变化趋势以持续性增加为主,其中25.23%的区域未来变化趋势无法确定。     

川藏铁路沿线植被覆盖度时空变化特征分析

基于MODIS-NDVI遥感数据反演了川藏铁路地区2000-2018年植被覆盖度,采用线性回归分析植被覆盖度的时空变化规律,利用相关分析法分析气候、地形等与植被覆盖度的相关关系.结果 表明:(1)2000-2018年川藏铁路沿线平均植被覆盖度为0.629,呈现波动上升趋势,2000-2012年为缓慢增长,2013-20...     

2000-2010年祁连山植被MODIS NDVI的时空变化及影响因素

利用2000-2010年间的MODIS/NDVI数据和对应的气候资料,研究了近10年来祁连山植被的时空变化及影响因素。结果表明:1)10年来,祁连山年最大化NDVI(MNDVI)增加了2.4%,植被改善、无变化和退化的面积分别占总面积的26.32%、66.42%和7.26%。植被改善的区域分布在冷龙岭、拉脊山、大通山、达坂山、青海南山、走廊南山、托来山等山地以及西宁盆地、湟水谷地周边地区,减少的区域分布在乌鞘岭、庄浪河、古浪河、大通河、石羊河、黑河、疏勒河等河流河谷。2)祁连山不同植被类型MNDVI的年际变化趋势不同。灌丛地、荒漠草原、高寒稀疏草甸MNDVI呈快速增加趋势,高山草原、高山灌丛草甸和高寒草甸MNDVI呈增加趋势,落叶阔叶林、针阔混交林、常绿针叶林MNDVI呈快速下降趋势。3)影响祁连山植被生长的主要因子是气温和降水,局部地区密集的人类活动也能成为影响植被生长的关键因子。     

基于NDVI的农牧交错带草地植被数量动态研究

为研究农牧交错带草地植被动态及其主要影响因子,为草地植被动态监测提供技术、理论支撑,本文选取地处农牧交错带的宁夏盐池为研究区域。在遥感影像处理软件ER-DAS IMAGING 8.7和多元统计软件SPSS 13等支持下,运用回归分析方法建立研究区最佳NDVI-生物量反演回归模型,在此基础上反演研究区2002-2005年植物生长季节(7-8月)植物生物量。2002-2005年研究区生物量等级类型动态研究结果表明:2002-2005年研究区植被年际间波动较大,等级Ⅳ(生物量3000-5000kg/hm2)、Ⅴ(5000-7000kg/hm2)、Ⅵ(>7000kg/hm2)是盐池县植被生长状况较好的区域,三个等级面积之和最大的是2003年,606955.1hm2,是4年中植被生长状况最好的一年,其次是2002年和2004年,分别为551733.12hm2和550895.4hm2,最小的是2005年为270909.9hm2。以植被生长状况最好的2003年的等级Ⅳ、Ⅴ、Ⅵ面积之和606955.1hm2为1,则2002年为0.909,2004年为0.908,2005年为0.446。分析植被年际间波动的原因主要有2个方面:一是气象因子如降水、温度等,其中降水对农牧交错带植被动态影响最大,但存在滞后效应。二是人为因子,包括有利因子和不利因子。有利因子如退耕还草、人工封育、撂荒等草地植被恢复及荒漠化防治措施以及相关的荒漠化防治政策法规的实施,不利因子如偷牧、滥垦、滥樵等。     

基于MODIS NDVI的青海高原植被覆盖时空变化特征分析

以2000-2014年MODIS NDVI数据为基础,综合利用MVC、SG滤波、Mann-Kendall检验等方法,对青海高原植被覆盖时空变化特征及其驱动因子进行了分析和研究。结果表明,受水资源、地形地貌类型等因素影响,研究区植被覆盖程度从东南向西北方向递减,植被生长发育周期区域差异性大,2000m以下的河湟谷地生长期最长,温度、降水量是其季节变化的重要驱动因子。15年间植被覆盖显著下降区域占11.3%,主要分布在柴达木盆地中部和青海高原东北部地区,32.1%的区域植被覆盖显著上升,分布在研究区中东部、青海湖、青南高原中部等地区,降雨量的增加和人类的改造活动是青海高原植被覆盖改善的重要影响因素。     

科尔沁沙地植被NDVI对太阳辐射照度变化的响应机制

在科尔沁沙地利用ASD光谱仪实测了7个不同植被盖度样方的反射光谱日变化,结合植被盖度与逐时太阳辐射照度数据,采用回归方法构建了不同植被盖度归一化植被指数(NDVI)与太阳辐射照度关系模型。结果表明:科尔沁沙地不同植被盖度NDVI对太阳辐射照度日变化具有相同的响应模式。NDVI在太阳辐射照度最小时段(6、16-18时)和平均时段(7-9、15时)易被高估0.03-0.14与0.02-0.08;其中盖度较低区域在太阳辐射照度最小时段(6、16-18时)NDVI被高估的幅度为0.13大于植被盖度较高的区域(0.03)。     

基于SPOT NDVI的中国东北地表植被覆盖动态变化及其机理研究

为了分析东北地表植被覆盖动态变化及其变化机理,选取该地区1998-2007年的SPOT/NDVI时间序列数据进行研究,并利用时间序列谐波分析(HANTS)算法对旬合成的NDVI数据进一步去云处理,根据处理后的结果,用一元线性回归趋势法定量描述了东北地表植被覆盖的动态变化。结果表明:近10年来中国东北地表植被覆盖整体得到改善的区域远比植被覆盖退化的区域面积大,其中严重退化的区域主要是内蒙古的东四盟地区,尤其是呼伦贝尔和科尔沁地区。     

Monitoring the impact of climate change andhuman activities on grassland vegetation dynamics in the northeastern Qinghai-Tibet Plateauof China during 2000-2015

Climate change and human activities can influence vegetation net primary productivity (NPP), a key component of natural ecosystems. The Qinghai-Tibet Plateau of China, in spite of its significant natural and cultural values, is one of the most susceptible regions to climate change and human disturbancesin the world. To assess the impact of climate change and human activities on vegetation dynamics in the grassland ecosystems ofthe northeastern Qinghai-Tibet Plateau, we applied a time-series trend analysis to normalized difference vegetation index (NDVI) datasets from 2000 to 2015 and compared these spatiotemporal variations with trends in climatic variables over the same time period. The constrained ordination approach (redundancy analysis) was used to determine which climatic variables or human-related factors mostly in?uenced the variation of NDVI. Furthermore, in order to determine whether current conservation measures and programs are effectivein ecological protection and reconstruction, we divided the northeastern Qinghai-Tibet Plateau into two parts: the Three-River Headwater conservation area (TRH zone) in the south and the non-conservation area (NTRH zone) in the north. The results indicatedan overall (73.32%)increasing trend of vegetation NPP in grasslands throughout the study area. During the period 2000-2015, NDVI in the TRH and NTRH zones increased at the rates of 0.0015/aand 0.0020/a, respectively.Specifically, precipitation accounted for 9.2% of the total variation in NDVI, while temperature accounted for 13.4%. In addition, variation in vegetation NPP of grasslands responded not only to long- and short-term changes in climate, as conceptualized in non-equilibrium theory, but also to the impact of human activities and their associated perturbations. The redundancy analysis successfully separated the relative contributions of climate change and human activities, of whichvillage populationand agricultural gross domestic product were the two most important contributors to the NDVI changes, explaining 17.8% and 17.1% of the total variationof NDVI (with the total contribution >30.0%), respectively. The total contributionpercentages of climate change and human activitiesto the NDVI variation were27.5% and 34.9%, respectively, inthe northeastern Qinghai-Tibet Plateau. Finally, our study shows that the grassland restoration in the study area was enhanced by protection measures and programs in the TRH zone, which explained 7.6% of the total variation in NDVI.     

Spatial and temporal variations of vegetation cover and the relationships with climate factors in Inner Mongolia based on GIMMS NDVI3g data

Variation in vegetation cover in Inner Mongolia has been previously studied by the remote sensing data spanning only one decade. However, spatial and temporal variations in vegetation cover based on the newly released GIMMS NDVI3g data spanning nearly thirty years have yet to be analyzed. In this study, we applied the methods of the maximum value composite(MVC) and Pearson's correlation coefficient to analyze the variations of vegetation cover in Inner Mongolia based on GIMMS NDVI3g data spanning from 1982 to 2013. Our results indicate that the normalized difference vegetation index(NDVI) increased at a rate of 0.0003/a during the growing seasons despite of the drier and hotter climate in Inner Mongolia during the past three decades. We also found that vegetation cover in the southern agro-pastoral zone significantly increased, while it significantly decreased in the central Alxa. The variations in vegetation cover were not significant in the eastern and central regions. NDVI is positively correlated with precipitation(r=0.617, P=0.000) and also with air temperature(r=0.425, P=0.015), but the precipitation had a greater effect than the air temperature on the vegetation variations in Inner Mongolia.     

Vegetation cover change and the driving factors over northwest China

In this paper the spatio-temporal variation of vegetation cover in northwest China during the period of 1982-2006 and its driving factors were analyzed using GIMMS/NDVI data. The annual average NDVI was increased with a rate of 0.0005/a in northwest China and there was an obvious difference between regions. The trend line slopes of NDVI were higher than 0.0005 in the Tianshan Moutains and Altay Mountains of Xinjiang,the Qilian Mountains of Gansu and the eastern part of Qinghai,which indicated the vegetation cover was significantly increased in these areas. The trend line slopes of NDVI were lower than 0.0005 in the southern region of Qinghai,the border regions of Shaanxi and Ningxia,the parts of Gansu and Tarim Basin,Turpan and Tuoli in Xinjiang,which indicated the vegetation cover was declined in these areas. The NDVI of woodland,grassland and cultivated land had an ascending tendency during the study period. The study shows that the vegetation cover change was caused by both natural factors and human activities in northwest China. The natural vegetation change,such as forests was influenced by climate change,while human activities were the main reason to the change of planting vegetation. The changes of vegetation covers for different elevations,slopes and slope aspects were quite different. When the elevation is exceeded to 4,000 m,the NDVI increasing trend was very low;the NDVI at the slope of less than 25° was increased by the ecological construction;the variation of NDVI on sunny slope was stronger than that on shady slope. The temperature rose significantly in recent 25 years in northwest China by an average rate of 0.67oC/10a,and precipitation increased by an average rate of 8.15 mm/10a after 1986. There was positive correlation between vegetation cover and temperature and annual precipitation changes. Rising temperature increased the evaporation and drought of soils,which is not conducive to plant growth,and the irrigation in agricultural areas reduced the correlation between agricultural vegetation NDVI and precipitation. The improvement of agricultural production level and the projects of ecological construction are very important causes for the NDVI increase in northwest China,and the ecological effect of large-scale ecological construction projects has appeared.     

Spatial distribution of vegetation and the influencing factors in Qaidam Basin based on NDVI

The spatial distribution of vegetation in Qaidam Basin was analyzed using GIMMS(Global Inventory Modeling and Mapping Studies) /NDVI(Normalized Difference Vegetation Index) data set from January 1982 to December 2006.Based on the data of precipitation,terrain,stream systems,land use and the map of vegetation distribution in Qaidam Basin,we studied the factors influencing the spatial distribution of vegetation.The results showed that the vegetation was generally low in Qaidam Basin and there was a clear semi-ring structure from southeast to northwest.In some areas,the existence of rivers,lakes and spring belts turned this semi-ring structure into a non-continuous state and formed distinct bright spots and continuous linear features.There were four main factors that affected the spatial distribution of vegetation coverage in Qaidam Basin,i.e.,precipitation,hydrological conditions,altitude and human activities.Precipitation and altitude have a correlation and determine the basic pattern of vegetation distribution in Qaidam Basin.The impacts of hydrological conditions and human activities were mainly embodied in partial areas,and often broke the pattern of vegetation distribution dominated by precipitation and altitude.