Spatial-temporal patterns of vegetation dynamics and their relationships to climate variations in Qinghai Lake Basin using MODIS time-series data

Global warming has led to significant vegetation changes in recent years. It is necessary to investigate the effects of climatic variations（temperature and precipitation） on vegetation changes for a better understanding of acclimation to climatic change. In this paper, we focused on the integration and application of multi-methods and spatial analysis techniques in GIS to study the spatio-temporal variation of vegetation dynamics and to explore the vegetation change mechanism. The correlations between EVI and climate factors at different time scales were calculated for each pixel including monthly, seasonal and annual scales respectively in Qinghai Lake Basin from the year of 2001 to 2012. The primary objectives of this study are to reveal when, where and why the vegetation change so as to support better understanding of terrestrial response to global change as well as the useful information and techniques for wise regional ecosystem management practices. The main conclusions are as follows：（1） Overall vegetation EVI in the region increased 6% during recent 12 years. The EVI value in growing seasons（i.e. spring and summer） exhibited very significant improving trend, accounted for 12.8% and 9.3% respectively. The spatial pattern of EVI showed obvious spatial heterogeneity which was consistent with hydrothermal condition. In general, the vegetation coverage improved in most parts of the area since nearly 78% pixel of the whole basin showed increasing trend, while degraded slightly in a small part of the area only.（2） The EVI change was positively correlated with average temperature and precipitation. Generally speaking, in Qinghai Lake Basin, precipitation was the dominant driving factor for vegetation growth; however, at different time scale its weight to vegetation has differences.（3） Based on geo-statistical analysis, the autumn precipitation has a strong correlation with the next spring EVI values in the whole region. This findings explore the autumn precipitation is an important indicator     

基于MODIS时序数据的青海湖流域植被时空变化特征及其与气候因子的关系(英文)

Global warming has led to significant vegetation changes in recent years. It is necessary to investigate the effects of climatic variations(temperature and precipitation) on vegetation changes for a better understanding of acclimation to climatic change. In this paper, we focused on the integration and application of multi-methods and spatial analysis techniques in GIS to study the spatio-temporal variation of vegetation dynamics and to explore the vegetation change mechanism. The correlations between EVI and climate factors at different time scales were calculated for each pixel including monthly, seasonal and annual scales respectively in Qinghai Lake Basin from the year of 2001 to 2012. The primary objectives of this study are to reveal when, where and why the vegetation change so as to support better understanding of terrestrial response to global change as well as the useful information and techniques for wise regional ecosystem management practices. The main conclusions are as follows:(1) Overall vegetation EVI in the region increased 6% during recent 12 years. The EVI value in growing seasons(i.e. spring and summer) exhibited very significant improving trend, accounted for 12.8% and 9.3% respectively. The spatial pattern of EVI showed obvious spatial heterogeneity which was consistent with hydrothermal condition. In general, the vegetation coverage improved in most parts of the area since nearly 78% pixel of the whole basin showed increasing trend, while degraded slightly in a small part of the area only.(2) The EVI change was positively correlated with average temperature and precipitation. Generally speaking, in Qinghai Lake Basin, precipitation was the dominant driving factor for vegetation growth; however, at different time scale its weight to vegetation has differences.(3) Based on geo-statistical analysis, the autumn precipitation has a strong correlation with the next spring EVI values in the whole region. This findings explore the autumn precipitation is an important indicator, and then, limits the plant growth of next spring.     

基于MODIS/EVI的内蒙古高原西部植被变化

内蒙古高原西部生态环境脆弱,是全球变化的敏感地带.为了解该区域植被覆盖的时空动态变化,根据2000—2012年MODIS/EVI影像,使用趋势分析和标准差分析方法,研究了近13年内蒙古高原西部植被生长状况及其空间格局动态变化.同时,根据《1:100万植被类型图》把研究区分为荒漠区、草原区、草甸区和灌丛区,以研究不同植被类型下的EVI变化情况.结果显示:内蒙古高原西部植被覆盖退化面积大于改善面积;植被退化区主要分布在内蒙古农牧交错带北部边缘,包含乌兰察布、呼和浩特、包头等市及大通河、疏勒河、黑河等河谷地带;植被增加区域分布在河西地区、河套地区和阿巴嘎旗附近;研究区植被稳定性存在明显的地域差异,波动较高的区域位于阴山南部、祁连山南北和阿巴嘎旗,与植被覆盖退化或者增加的区域基本吻合;仅荒漠区植被覆盖水平上升,草甸、草原区植被覆盖退化严重.     

Spatio-temporal Variation of Vegetation Ecological Quality and Its Response to Climate Change in Rocky Desertification Areas in Southwest China during 2000-2020

Vegetation restoration is the primary task of ecological reconstruction and rocky desertification control in Karst areas. With vegetation net primary productivity and coverage as two key indicators, a vegetation ecological quality evaluation model was built based on meteorological and remote sensing data. Spatiotemporal variation of vegetation ecological quality index and its response to climate change in rocky desertification areas in Southwest China during 2000-2020 were also analyzed by using the difference method and linear trend method. The results showed that: (1) Vegetation ecological quality in rocky desertification areas in Southwest China showed a fluctuating upward trend during 2000-2020. In 2020, the vegetation ecological quality index reached 69.7, which was 19.9% and 9.3% higher than the averaged values for 2000 and 2000-2019, respectively, ranking the fourth highest since 2000. (2) Vegetation ecological quality of the rocky desertification areas in Yunnan, Guangxi and Guizhou provinces have been improved by 89.2%, 99.2% and 98.5%, respectively, from 2000 to 2020, with their vegetation ecological quality index values increasing by 0.5-0.75 per year in southeast Yunnan, most areas in Guizhou and northwest Guangxi. (3) Precipitation was an important meteorological factor affecting the vegetation ecological quality in rocky desertification areas. The vegetation ecological quality index in the northwest and central Yunnan rocky desertification areas has been rising slowly, but with localized declines at a yearly rate of nearly 0.25 caused by climatic warming and drying.     

祁连山区植被物候遥感监测与变化趋势

基于1982-2006年GIMMS NDVI时间序列数据,利用Double Logistic拟合方法提取了祁连山区植被的生长季始期、生长季末期和生长季长度参数,分析了植被物候期的时间变化趋势及空间分异特征。结果表明:祁连山植被从东南向西北逐渐变绿,而从西北到东南逐渐变黄,植被生长季呈现出东南地区比西北地区长、河谷地区比高山地区长的特征。25年内植被年生长季始期呈提前趋势,提前幅度为0.044 d·a^-1,年代趋势为延迟-提前-延迟;年生长季末期也呈提前趋势,提前幅度为0.059 d·a^-1,年代趋势为延迟-提前;生长季长度略有缩短,缩短幅度为0.015 d·a^-1,年代趋势为缩短-延长-缩短。25年内祁连山区植被生长季始期、末期提前不明显的区域主要为高山地区,分别占51.46%、42.77%;生长季始期、末期推迟不明显区域主要为河谷地区,分别占44.41%、52.91%;植被生长季高山地区延长不明显,河谷地区缩短不明显,总体上植被物候没有出现明显变化。     

近10 a青藏高原干湿状况及其与植被变化的关系研究

植被是陆地生态系统中最重要、同时也是气候变化最敏感的组分,而高原植被系统行为往往比其他地区能更早、更明显地预兆全球变化。探讨青藏高原区域干湿状况及其与植被变化的关系有助于更好地认识和理解陆地生态系统对气候变化的响应和适应机理,对高原生态安全屏障计划的实施以及全球生态建设有重要意义。基于地面气象台站观测数据和MODIS EVI数据集,2001-2010年生长季干湿状况和植被覆盖的时空变化格局,对青藏高原干湿状况与植被覆盖变化的关系进行了分析与探讨。结果表明：（1）高原整体上呈现由东南向西北渐干的趋势,干旱及半干旱区占高原总面积的67%。10 a间高原有25%的区域在逐渐变干,且南北差异明显;（2）高原生长季EVI的空间格局与干湿格局相近,且东西部界线分明。10 a间高原植被活动由东南向西北整体上呈现“退化-增强-变化不大”的规律;（3）区域干湿程度对EVI空间格局差异有显著影响,特别是在占高原面积44%的半干旱区,两者相关性最大。人为干扰对高原EVI变化的作用不明显,但EVI与干湿程度相关性相对偏小的区域人为干扰程度往往较大;（4）从高原96个气象站点生长季[EVI]对干燥度指数变化的敏感性来看,敏感程度较大的气象站点主要集中在高原东北部、高原中部及雅鲁藏布江中上游区域,60%以上的气象站点随着干旱程度的加深植被呈退化趋势。     

黄土高原植被恢复潜力研究

黄土高原从1999年开始大规模退耕还林（草）,植被覆盖发生了较大变化,对黄土高原植被恢复现状和恢复潜力进行评估具有重要意义。本文使用1999-2013年SPOT VEG NDVI数据,采用线性回归、Hurst指数分析法、统计学方法以及地理空间分析技术,对黄土高原植被恢复状况和潜力进行了探讨。结论主要为：① 1999年退耕还林（草）以来,黄土高原植被覆盖度呈显著上升趋势,黄土高原三分之二地区的植被将会持续改善;② 植被响应曲线分析表明,黄土区植被覆盖度和干旱指数呈显著的指数关系,且缓坡相关性大于陡坡。土石山区植被响应函数为线性函数,相关系数下降;③ 整个黄土高原地区平均植被恢复潜力为69.75%。植被恢复潜力值东南高而西北低,黄土高原东南地区植被恢复状况较好,其植被恢复潜力指数较小,而植被恢复潜力指数较高的地区主要为北方风沙区及西部丘陵沟壑区;④ 不同降水量条件下,植被恢复速度差别显著,其中降水量在375~575 mm之间的地区,植被恢复最快。植被恢复措施应该“因水制宜”,避免因造林带来的土壤干化加剧。研究结果以期为黄土高原生态文明建设提供科学支撑。     

1981-2015年新疆生产建设兵团植被生长变化特征

新疆生产建设兵团的农垦事业为新疆的经济发展和社会稳定做出了重大贡献,研究其植被生长变化特征对于评价当地农垦发展和生态环境状况具有重要意义。采用1981-2015年GIMMS-NDVI和MODIS-NDVI数据对新疆生产建设兵团植被生长时空状况进行了研究,结果显示：（1）兵团植被在年内生长变化方面与气温变化趋势相一致;年际变化方面,NDVI在2007、2008、2010、2012年和2013年相对较高,1982-1986年和1989年相对较低;年代际变化方面,植被生长在20世纪80年代相对较差、90年代次之、2000-2009年相对较好、2010-2015年最好。（2）空间格局差异方面,植被生长状况呈变差趋势的面积占总面积的37.69%,主要分布在各团场驻地建筑区,植被生长状况趋于改善的面积占总面积的62.31%,主要分布在团场驻地周边地区;兵团植被生长状况以轻度、中度和特重度波动改善为主,分别占总面积的17.29%、15.55%和12.35%,重度和特重度波动退化面积最小,仅占总面积的5.12%和2.11%。     

三工河流域平原区蒸发量变化特征及影响因素

采用线性倾向估计、滑动平均和Mann-Kendall非参数统计检验等方法,分析了三工河流域平原区1981-2012年蒸发量变化特征及主要影响因子,并通过多元相关模型定量给出了各气象因子对蒸发量变化的贡献程度。结果表明：三工河流域平原区近32 a蒸发量呈显著下降趋势,春夏秋冬四季的蒸发量也呈显著减少的趋势。春季和夏季蒸发量的大幅减少对年蒸发量减少的贡献率较大,冬季蒸发量在1985年和1989年发生突变。影响蒸发量的因子中,降水、日照时数、相对湿度、风速和气压均呈下降趋势,其中日照时数、相对湿度和风速下降趋势显著,而气温上升趋势明显。以1981-1990年为基准期,1991-2000年风速和日照时数减少对蒸发量减少的贡献率分别为85.27%、20.70%,其它影响因素对蒸发量减少的贡献率为-5.97%;而2001-2012年风速和日照时数的减少对蒸发量减少的贡献率分别为52.32%和39.91%,其它影响因素的贡献率为7.77%。     

1998—2012年黄河流域植被覆盖变化时空分析

利用黄河流域1998—2012年SPOT-NDVI数据及同期119个气象站的降水数据,计算每个像元的NDVI变化趋势,并结合植被降水利用效率来分析近15年来黄河流域植被覆盖的时空变化特征。结果表明：（1） 多年平均的植被指数有明显的空间差异性,随着纬度的增加,NDVI平均值呈降低趋势;（2） 从时间序列来看,黄河流域的植被覆盖呈逐年增加趋势,其中黄河上游NDVI值增长最为缓慢,中游保持稳定增长,下游增长最快;（3） 近15年来黄河流域植被覆盖的改善区域面积大于退化区域,植被恢复明显。最后,结合NDVI变化趋势和植被降水利用效率对上述结果进行了验证。     

京津冀地区不透水表面覆盖率的时空演变及其对植被的影响

基于不透水表面和MODIS增强型植被指数（EVI）数据,辅以分段线性回归、趋势分析等方法,定量分析2000—2018年京津冀不透水表面覆盖率（ISP）的时空演变及其对植被的影响。结果表明：① 京津冀ISP呈显著增加的趋势,增速为0.024%/a（P<0.01）。分阶段来看,2000—2010年和2011—2018年ISP均呈显著增加趋势,增速分别为0.019%/a（P<0.01）和0.037%/a（P<0.01）,后一阶段的增速快于前一阶段;② 空间上,ISP快速增加的区域主要位于城市和近郊,缓慢增加和增加的区域主要位于主城区和农村;③ 从不同ISP区域ΔEVI的时间变化趋势来看,城区、近郊和远郊的ΔEVI均呈显著下降趋势（P<0.05）的地市分别有6个、6个和3个。主城区的ΔEVI呈显著增加趋势的地市有3个（P<0.05）。从EVI的空间变化趋势来看,显著增加的区域主要位于北京、天津等市的主城区,显著减少的区域主要位于北京、天津、石家庄等地市的近郊和远郊;④ 从EVI随ISP的空间变化趋势看,所有地市EVI随ISP的增加均呈显著减小的趋势（P<0.01）。减小趋势最大和最小的地市分别为秦皇岛和张家口,其下降速率为-0.0081/a和-0.0043/a。从时间变化来看,京津冀的EVI与ISP呈显著负相关,其相关系数为-0.4912。研究结果可为中国城市快速扩张过程中的植被变化提供理论参考和科学实践。     

青海省都兰县察汗乌苏绿洲植被覆盖度变化研究

为研究青海省都兰县察汗乌苏绿洲植被覆盖度变化,利用归一化植被指数NDVI提取察汗乌苏绿洲不同时期的植被覆盖度等级图,定量分析评价植被覆盖度的多年变化。结果表明,近16 a来,察汗乌苏绿洲植被覆盖度总体呈现波动增长趋势,2001—2006年期间各植被覆盖等级变化幅度明显高于1990—2001年期间的变化幅度,1990—2001年植被整体向好的方向发展,有50 017.50 hm2的极低覆盖度植被转变为更高覆盖度植被,2001—2006年增加了6 026.85 hm2的极低覆盖度植被,并有4 048.47 hm2的高覆盖度植被减少,说明仍存在局部退化。影响都兰县察汗乌苏绿洲植被覆盖度变化的主要因子是生态工程措施、气候因素和水资源因素。研究结果可以为该区域植被恢复和荒漠化防治提供理论支撑。     

The dynamic response of forest vegetation to hydrothermal conditions in the Funiu Mountains of western Henan Province

This paper uses HJ-1 satellite multi-spectral and multi-temporal data to extract forest vegetation information in the Funiu Mountain region. The S-G filtering algorithm was employed to reconstruct the MODIS EVI (Enhanced Vegetation Index) time-series data for the period of 2000–2013, and these data were correlated with air temperature and precipitation data to explore the responses of forest vegetation to hydrothermal conditions. The results showed that: (1) the Funiu Mountain region has relatively high and increasing forest coverage with an average EVI of 0.48 over the study period, and the EVI first shows a decreasing trend with increased elevation below 200 m, then an increasing trend from 200–1700 m, and finally a decreasing trend above 1700 m. However, obvious differences could be identified in the responses of different forest vegetation types to climate change. Broad-leaf deciduous forest, being the dominant forest type in the region, had the most significant EVI increase. (2) Temperature in the region showed an increasing trend over the 14 years of the study with an anomaly increasing rate of 0.27°C/10a; a fluctuating yet increasing trend could be identified for the precipitation anomaly percentage. (3) Among all vegetation types, the evergreen broad-leaf forest has the closest EVI-temperature correlation, whereas the mixed evergreen and deciduous forest has the weakest. Almost all forest types showed a weak negative EVI-precipitation correlation, except the mixed evergreen and deciduous forest with a weak positive correlation. (4) There is a slight delay in forest vegetation responses to air temperature and precipitation, with half a month only for limited areas of the mixed evergreen and deciduous forest.     

21世纪以来青藏高寒草地的变化特征及其对气候的响应

利用遥感数据和气象观测资料探索气候因子对区域植被变化的驱动作用具有重要意义。以1980-2012年气象数据和2000-2012年MODIS-NDVI数据为数据源,借助线性回归和相关分析分别分析了青海和西藏两个地区21世纪以来气候变化对青藏高寒草地的影响机制。结果表明：（1）1980-2012年,青海和西藏地区均呈暖湿化的发展趋势。但21世纪以来,西藏地区降水呈不显著的减少趋势;整个青藏高原中部和西部地区增温趋势明显（>0.05 ℃·a-1）。（2）在年际尺度（2000- 2012年）上,青海地区NDVI呈显著增加的趋势,增长率为0.003·a-1（P<0.05）;西藏地区NDVI无变化趋势,区域尺度统计中植被退化与改善相互抵消。在空间上,青藏高原东北部地区NDVI呈良性趋势,部分区域增长斜率超过0.01·a-1。青藏高原南部地区NDVI呈变差趋势,变化斜率为0.008·a-1。（3）区域上的相关分析显示,在青海地区,降水量的增加和温度的升高共同促进了该区域植被的良性发展趋势;在西藏地区,降水量的减少和温度的升高可能是南部地区植被变差的重要原因。     

Effect of Land Use and Land Cover Change on the Changes in Net Primary Productivity in Karst Areas of Southwest China: A Case Study of Huanjiang Maonan Autonomous County

Karst areas in southwest China have experienced significant land cover and land use change (LUCC) due to utilization for human activity and a comprehensive rocky desertification control project (RDCP) since 2008. It is important to quantify the effect of LUCC on ecosystem productivity in this region for assessing the overall benefit of this ecological restoration project. In this study, we used using MODIS land cover and NPP products to investigate the relative contribution of LUCC to the change in net primary productivity (NPP) during 2008-2013 in Huanjiang County, one of first one hundred pilot counties to implement RDCP. Our results show that NPP increased in 95.53% of the county, and the average growth of NPP in non-rocky desertification area was higher than in rocky desertification or potential rocky desertification areas. LUCC has an important contribution (25.23%) to the NPP increase in the county, especially in the LUCC area (70.97%), which increased the average NPP by 3.9% and 10.5%, respectively. Across the six RDCP regions in the county, the average increase in NPP for the vegetation restoration measure of governed karst area is significantly greater than in the ungoverned karst area, and the positive change in NPP increased with the increasing implementation area of the vegetation restoration measure.     

2000-2012年青海湖流域NPP时空分布特征

利用青海湖流域及周边地区气象资料和MODIS遥感影像等数据,结合地理信息系统技术和植被净初级生产力(NPP)估算模型(CASA模型),确定了2000-2012年青海湖流域NPP值,并评价了其时空分布特征。结果表明:2000-2012年青海湖流域年均NPP为4.77×10¹² g,空间分布以青海湖为中心,由低到高呈环带状,并呈由东南向西北递减趋势,在青海湖北侧河流中游地区年均NPP达到最高,为374.19 g·m^-2。2000-2012年NPP呈波动中逐渐增长趋势,年均增加4.81×10¹⁰ g;NPP年内变化显著,7月NPP达到全年最高值,占全年的28.77%。13年间流域内大部分地区NPP呈增长趋势,显著增长区主要分布在共和县江西沟乡、石乃亥乡和天峻县周围;青海湖北侧哈尔盖河上游、沙柳河中游地区则是主要减少区。多元回归分析表明归一化植被指数(NDVI)和降水是青海湖流域NPP的主要影响因素。     

1971-2010年三江源地区干湿状况变化的空间特征

 依据1971-2010年地面观测气象数据,计算了三江源地区湿润指数。利用经验正交函数分解（EOF）和偏相关系数,对近40 a三江源地区干湿状况变化的时空特征及其影响因素进行了分析。结果表明:三江源地区干湿状况的变化在其北部与南部、东部与西部间存在明显反相位变化特征。北部和东部的部分区域分别在20世纪90年代和21世纪后表现出气候湿润化趋势,其余大部地区的持续干旱化趋势始于20世纪80年代初,其中南部与西部变干趋势显著,其湿润指数线性趋势率达到-8%/10 a。虽然三江源地区干湿状况主要决定于降水量和相对湿度的变化,但20世纪90年代中期后气温的显著上升,使得气温也成为关键的影响因子之一,即使在降水明显增加的背景下,也引起三江源主体区域湿润指数的明显下降。气候变暖情景下,北部和东部地区在近十几年暖湿化趋势明显,其余大部地区表现为不同程度的暖干化趋势。     

退耕还林还草工程对黄土高原植被总初级生产力的影响

采用Landsat解译的2000年和2015年土地利用/覆盖数据和VPM模型（Vegetation Photosynthesis Model）模拟的2000~2016年总初级生产力（Gross Primary Productivity, GPP）数据,识别出了近16 a黄土高原退耕还林还草的空间范围,并估算了GPP的年际变化趋势。在此基础上,对比分析了退耕区和未退耕区GPP年际变化的差异,从而揭示退耕还林还草工程对GPP年际变化的影响。结果显示,2000~2015年,黄土高原退耕还林还草面积约3.5万km ²,占2000年耕地面积的16.8%。期间,GPP呈增加趋势,GPP显著上升区域占全区面积的67.3%,平均增速24.1 g/(m ²?a)（以C计,下同）。虽然退耕区多年平均GPP低于未退耕区,但退耕区GPP年际增速和相对变化率明显高于未退耕区,分别提高了5.9 g/(m ²?a)和1.5%。     

三江平原NDVI时空变化及其对气候变化的响应

基于2000—2014年生长季MODIS NDVI数据和同期降水、平均气温的格点数据，采用趋势分析法、SPEI指数、相关分析法，对三江平原NDVI时空变化特征和对气候变化的响应进行了分析。结果表明：近15年三江平原区生长季的NDVI以0.017/10a的速率呈缓慢上升趋势。其中NDVI显著增加和极显著增加的面积占比分别为13.43%和12.55%，NDVI变化趋势轻度改善的面积较大，占比为25.52%；三江平原地区生长季的多年平均气温总体呈下降趋势，降水量呈上升趋势，总体上生长季标准化降水蒸散指数（SPEI）数值呈上升趋势，干旱化逐年减弱，中等干旱状况得到缓解，渐渐过渡到轻微湿润状态，对植被覆盖面积的增加有促进作用，也为该区域的生态环境恢复提供了有利条件；三江平原地区生长季NDVI与生长季气温、降水量及SPEI主要呈正相关，与降水呈正相关面积占72.64%，与SPEI呈正相关的面积占70.51%，与气温呈正相关的面积占56.73%。NDVI与降水的相关性最高，说明降水是三江平原植被生长的主导气候因子。     

气候变化与人类活动对玛曲地区生态环境的影响

根据玛曲1971—2005年的气温、降水、大风、沙尘暴等资料的变化及其对该地区生态环境的影响作了分析。结果表明：30 a来,玛曲地区的气温在逐渐升高,降水有下降趋势,蒸发量也有下降趋势,年大风、沙尘暴年发生日数也呈下降趋势,干旱程度表现出增加趋势。人类的过度放牧和滥伐乱挖造成玛曲地区植被生产力下降、草原退化、土地沙漠化加剧。气候暖干化和人类不合理的开采活动是造成该地区生态环境恶化的重要原因.