Spatiotemporal changes in vegetation coverage and its driving factors in the Three-River Headwaters Region during 2000–2011简

The Three-River Headwaters Region （TRHR）, which is the source area of the Yangtze River, Yellow River, and Lancang River, is of key importance to the ecological secu- rity of China. Because of climate changes and human activities, ecological degradation oc- curred in this region. Therefore, ＂The nature reserve of Three-River Sou,＇ce Regions＂ was established, and ＂The project of ecological protection and construction for the Three-River Headwaters Nature Reserve＂ was implemented by the Chinese government. This study, based on MODIS-NDVI and climate data, aims to analyze the spatiotemporal changes in vegetation coverage and its driving factors in the TRHR between 2000 and 2011, from three dimensions. Linear regression, Hurst index analysis, and partial correlation analysis were employed. The results showed the following： （1） In the past 12 years （2000-2011）, the NDVI of the study area increased, with a linear tendency being 1.2%/10a, of which the Yangtze and Yellow River source regions presented an increasing trend, while the Lancang River source region showed a decreasing trend. （2） Vegetation coverage presented an obvious spatial difference in the TRHR, and the NDVI frequency was featured by a bimodal structure. （3） The area with improved vegetation coverage was larger than the degraded area, being 64.06% and 35.94%, respectively during the study period, and presented an increasing trend in the north and a decreasing trend in the south. （4） The reverse characteristics of vegetation cov- erage change are significant. In the future, degradation trends will be mainly found in the Yangtze River Basin and to the north of the Yellow River, while areas with improving trends are mainly distributed in the Lancang River Basin. （5） The response of vegetation coverage to precipitation and potential evapotranspiration has a time lag, while there is no such lag in the case of temperature. （6） The increased vegetation coverage is mainly attributed to the warm-wet climate change and the implementation of the ecological protection project.     

2000-2011 年三江源区植被覆盖时空变化特征

基于MODIS-NDVI 数据,辅以线性趋势分析、Hurst 指数及偏相关系数等方法,本文从三个尺度分析了近12 年三江源区植被覆盖时空变化特征、未来趋势及其驱动因素。结果表明:(1) 近12 年三江源区植被覆盖呈现增加趋势,增速为1.2%/10a,其中长江源区、黄河源区植被均呈增加趋势,而澜沧江源区植被呈下降趋势。(2) 三江源区植被覆盖具有显著的区域差异,且NDVI频度呈现“双峰”结构。(3) 近12 年三江源区植被覆盖呈增加趋势和减少趋势的面积分别占64.06%和35.94%,且表现为源区北部增加、南部减少的空间格局。(4) 三江源区植被变化的反向特征显著,植被变化由改善趋势转为退化趋势的区域主要分布在长江源区和黄河源区的北部,而由退化趋势转为改善趋势的区域主要分布在澜沧江源区。(5) 三江源区植被对降水和潜在蒸散的响应存在时滞现象,而对气温的响应不存在时滞现象。(6) 三江源区植被覆盖的增加主要归因于气候暖湿化以及生态保护工程的实施。     

三江源气候变化及其对径流的驱动分析

以1965-2004 年三江源地区12 个气象台站的降水和气温资料以及长江源区直门达、黄河源区唐乃亥和澜沧江源区昌都水文站的径流资料为基础,分析三江源地区的降水、气温和径流的变化趋势,并采用Mann-Kendall-Sneyers 方法进行趋势显著性检验;采用Makkink 公式计算三江源区12 个气象站点的潜在蒸发,建立三江源区降水和潜在蒸发对径流的驱动模型,并对气候变化(降水和气温的变化) 对径流的驱动进行情景分析。研究表明：1965-2004 年三江源区气温升高,径流减少,并且气温和径流都在1994 年发生突变,但降水的变化趋势不明显。降水和潜在蒸发对径流深的驱动模型表明三江源区降水对径流起正向的驱动作用,潜在蒸发对径流起负向的驱动作用,具体来说,澜沧江源区潜在蒸发对径流的驱动力最大,长江源区次之,黄河源区最小。借助驱动模型对三江源气候变化(降水和气温的变化) 对径流的影响进行情景分析,结果显示,降水和气温对径流的驱动在总体上虽然分别是正、负方向上的驱动,但在具体情景下其各自的驱动作用又呈现出波动的特征。     

Climatic Changes Dominant Interannual Trend in Net Primary Productivity of Alpine Vulnerable Ecosystems

The Three-River Headwaters (TRH), which is the source area of Yangtze River, Yellow River and Lancang River, is vulnerable and sensitive, and its alpine ecosystem is considered an important barrier for China’s ecological security. Understanding the impact of climate changes is essential for determining suitable measures for ecological environmental protection and restoration against the background of global climatic changes. However, different explanations of the interannual trends in complex alpine ecosystems have been proposed due to limited availability of reliable data and the uncertainty of the model itself. In this study, the remote sensing-process coupled model (GLOPEM-CEVSA) was used to estimate the net primary productivity (NPP) of vegetation in the TRH region from 2000 to 2012. The estimated NPP significantly and linearly correlated with the above-ground biomass sampled in the field (the multiple correlative coefficient R² = 0.45, significant level P < 0.01) and showed better performance than the MODIS productivity product, i.e. MOD17A3, (R² = 0.21). The climate of TRH became warmer and wetter during 1990-2012, and the years 2000 to 2012 were warmer and wetter than the years1990-2000. Responding to the warmer and wetter climate, the NPP had an increasing trend of 13.7 g m^-2 (10 yr)^-1 with a statistical confidence of 86% (P = 0.14). Among the three basins, the NPP of the Yellow River basin increased at the fastest rate of 17.44 g m^-2 (10 yr)^-1 (P = 0.158), followed by the Yangtze River basin, and the Lancang River, which was the slowest with a rate of 12.2 g m^-2 (10 yr)^-1 and a statistical confidence level of only 67%. A multivariate linear regression with temperature and precipitation as the independent variables and NPP as the dependent variable at the pixel level was used to analyze the impacts of climatic changes on the trend of NPP. Both temperature and precipitation can explain the interannual variability of 83% in grassland NPP in the whole region, and can explain high, medium and low coverage of 78%, 84% and 83%, respectively, for grassland in the whole region. The results indicate that climate changes play a dominant role in the interannual trend of vegetation productivity in the alpine ecosystems on Qinghai-Tibetan Plateau. This has important implications for the formulation of ecological protection and restoration policies for vulnerable ecosystems against the background of global climate changes.     

The 30m-NDVI-based Alpine Grassland Changes and Climate Impacts in the Three-River Headwaters Region on the Qinghai-Tibet Plateau from 1990 to 2018

The response of long-term vegetation changes and climate change has been a hot topic in recent research. Previously, a Landsat-based fusion model was developed and used to produce a dataset of normalized vegetation index (NDVI) for the Three-River Headwater region on the Qinghai-Tibet Plateau with a spatial resolution of 30 m and the time spanning the nearly 30 years from 1990 to 2018. In this study, the NDVI was applied to an analysis of the spatial and temporal changes in the alpine grassland and the impacts from climate change using the Theil-Sen Median method and linear regression. The results showed that: (1) The regional mean NDVI was 0.39 and showed a spatial pattern of decreasing from the southeast to the northwest in the recent three decades. Among the three parks, the Lancang River Park had the highest NDVI (0.43), followed by the Yellow River Park (0.38) and Yangtze River Park (0.23). (2) An upward trending was found in the NDVI time series at a rate of 0.0031 yr^-1 (R² =0.62, P < 0.01) over the whole period of 1990-2018. The increasing rate (0.00649 yr^-1, R² =0.71, P < 0.01) in the latter period of 2005-2018 was nearly 2.3 times of that (0.00284 yr^-1, R² =0.31, P < 0.01) in the previous period of 1990-2005. In the latest periods, the three parks experienced rates that were 2.3 to 63 times the corresponding values in the early period. (3) The NDVI is correlated more positively with temperature than precipitation. The impacts of climate change decreased along with the coverage fraction from the higher, median and then lower levels. The climate change can explain 34% of the variability in the NDVI time series of the areas with a higher fraction of grassland coverage, while it was 31% for the median fraction and 20% for the lower fraction. This study is the first to use the 30 m NDVI dataset spanning nearly 30 years to analyze the spatial and temporal variability and climate impacts in the alpine grasslands of the Three-River Headwater region of the Qinghai-Tibet Plateau. The results provide a basis for assessments on the ecological management effects and ecological quality based on long-term baseline data with a higher spatial resolution.     

生态保护工程和气候变化对长江源区植被变化的影响量化

分析长江源区生态保护工程和气候变化对植被变化的影响程度,对于长江源区生态工程的生态效益评估,以及区域植被适应性生态管理政策的制定具有重要意义。因此,本文基于1982-2015年的归一化植被指数数据（Normalized Difference Vegetation Index, NDVI）和气象数据,分析长江源区植被NDVI的时空变化规律,构建预测植被NDVI对气候因子响应的人工神经网络模型,在此基础上,在年和季节尺度上量化气候变化和生态保护工程对长江源区植被变化的影响程度。结果表明：① 在长江源区气候条件变化和生态保护工程影响下,长江源区植被退化得到遏制,植被生长呈好转趋势;② 海拔相对较低的通天河附近植被NDVI增加幅度较大,高海拔的沱沱河和当曲流域的植被NDVI增加幅度相对较小;③ 长江源区植被NDVI对气候因子响应存在1~2月的滞后性。构建的人工神经网络模型的拟合优度参数人工神经网模型具有较高的预测精度,可以用来模拟植被NDVI对气候因子的响应;④ 年尺度的植被NDVI增加受到生态保护工程的影响程度（58.5%）大于气候变化的影响程度（41.5%）。生长季生态保护工程对NDVI的影响程度（63.3%）大于气候变化对NDVI的影响程度（36.7%）,而非生长季气候变化是影响长江源区植被生长的关键要素（52.8%）。研究结果有助于为长江源区植被生态系统恢复、管理和利用战略的科学制定提供决策依据。     

三江源地区植被指数下降趋势的空间特征 及其地理背景

利用8km分辨率的Pathfinder NOAA/AVHRR-NDVI数据,结合1km分辨率的DEM,1 ∶ 250000道路、居民点、水系数据以及野外调查数据,分析了植被指数变化总体态势、植被指数变化与海拔及与距道路、水源和居民点距离之间的关系,探讨了三江源区1981~2001年间植被指数变化趋势和空间分异特征。结果表明:①三江源地区植被指数变化以下降趋势为主,下降区域占源区总面积的18.92%,增加区域占13.99%;②不同植被和冻土类型下的植被指数下降特征:灌丛区和森林区下降率最高,下降率与各类型区的居民点密度、生计方式有关;植被指数下降程度与冻土类型关系不明显;③植被指数下降的区域差异明显:下降率各区域分别为长江源区13.56%、黄河源区32.51%和澜沧江源区18.1%;④植被指数下降率随着距道路、河流的距离增加而逐渐减小;下降率在距居民点18~24km的缓冲带上达到最高后随着距离增大而下降;植被指数下降率随着海拔高程的升高呈"低－高－低－高"态势,下降率与居民点的分布高度相关。     

江河源区NDVI时空变化及其与气候因子的关系(英文)

The source regions of the Yangtze and Yellow rivers are important water conservation areas of China. In recent years, ecological deterioration trend of the source regions caused by global climate change and unreasonable resource development increased gradually. In this paper, the spatial distribution and dynamic change of vegetation cover in the source regions of the Yangtze and Yellow rivers are analyzed in recent 10 years based on 1-km resolution multitemporal SPOTVGT-DN data from 1998 to 2007. Meanwhile, the correlation relationships between air temperature, precipitation, shallow ground temperature and NDVI, which is 3×3 pixel at the center of Wudaoliang, Tuotuohe, Qumalai, Maduo, and Dari meteorological stations were analyzed. The results show that the NDVI values in these two source regions are increasing in recent 10 years. Spatial distribution of NDVI which was consistent with hydrothermal condition decreased from southeast to northwest of the source regions. NDVI with a value over 0.54 was mainly distributed in the southeastern source region of the Yellow River, and most NDVI values in the northwestern source region of the Yangtze River were less than 0.22. Spatial changing trend of NDVI has great difference and most parts in the source regions of the Yangtze and Yellow rivers witnessed indistinct change. The regions with marked increasing trend were mainly distributed on the south side of the Tongtian River, some part of Keqianqu, Tongtian, Chumaer, and Tuotuo rivers in the source region of the Yangtze River and Xingsuhai, and southern Dari county in the source region of the Yellow River. The regions with very marked increasing tendency were mainly distributed on the south side of Tongtian Rriver and sporadically distributed in hinterland of the source region of the Yangtze River. The north side of Tangula Range in the source region of the Yangtze River and Dari and Maduo counties in the source region of the Yellow River were areas in which NDVI changed with marked decreasing tendency. The NDVI change was980 Journal of Geographical Sciences positively correlated with average temperature, precipitation and shallow ground temperature. Shallow ground temperature had the greatest effect on NDVI change, and the second greatest factor influencing NDVI was average temperature. The correlation between NDVI and shallow ground temperature in the source regions of the Yangtze and Yellow rivers increased significantly with the depth of soil layer.     

2000-2012年祁连山植被覆盖变化及其与气候因子的相关性

研究祁连山地区植被覆盖变化及其与气候因子的响应关系对这一地区土地利用总体特征以及对区域及全球气候和环境变化都将产生深远的意义。利用2000-2012年美国国家航空航天局提供的MODIS NDVI数据并结合相应的气候资料,通过对逐像元信息的提取和分析,运用均值法、斜率分析法、相关分析法,研究了2000-2012年不同季节祁连山植被覆盖的时空变化及其与气候因子的相关性。结果表明:13 a来祁连山植被覆盖整体上呈增加趋势,其中春季植被改善最为明显,秋季次之;植被覆盖变化在不同季节都存在明显的空间差异;不同季节植被与气温、降水的时滞效应不尽相同;祁连山春季大部分地区NDVI与气温呈显著正相关,夏季NDVI与降水呈显著正相关,秋、冬季NDVI与降水、气温的相关性不明显。     

三江源地区气候变化及其对径流的驱动分析(英文)

Based on the precipitation and temperature data of the 12 meteorological stations in the "Three-River Headwaters" region and the observed runoff data of Zhimenda in the headwater sub-region of the Yangtze River, Tangnaihai in the headwater sub-region of the Yellow River and Changdu in the headwater sub-region of the Lancang River during the period 1965-2004, this paper analyses the trends of precipitation, temperature, runoff depth and carries out significance tests by means of Mann-Kendall-Sneyers sequential trend test. Makkink model is applied to calculate the potential evaporation. The runoff model driven by precipitation and potential evaporation is developed and the influence on runoff by climate change is simulated under different scenarios. Results show that during the period 1965-2004 the temperature of the "Three-River Headwaters" region is increasing, the runoff of the three hydrological stations is decreasing and both of them had abrupt changes in 1994, while no significant trend changes happen to the precipitation. The runoff model suggests that the precipitation has a positive effect on the runoff depth, while the potential evaporation plays a negative role. The influence of the potential evaporation on the runoff depth of the Lancang River is found to be the significant in the three rivers; and that of the Yellow River is the least. The result of the scenarios analysis indicates that although the precipitation and the potential evaporation have positive and negative effects on runoff relatively, fluctuated characteristics of individual effect on the runoff depth in specific situations are represented.     

近20年来黄河流域植被覆盖变化分析

利用1982～1999年AVHRR-NDVI数据和对应年份黄河流域气象观测数据，通过计算、分析春季、夏汛及伏秋黄河流域NDVI距平值和湿润指数距平值的年际变化，得出了20世纪80年代至90年代初黄河流域气候相对湿润，90年代中后期相对干旱，植被覆盖状况总体一直处于上升趋势的结论，并评估了黄河流域近20年来生态保护和建设工作成效。     

近30 年来青海三江源地区草地退化的时空特征

在20 世纪70 年代中后期MSS 图像、90 年代初期TM 图像和2004 年TM/ETM 图像支 持下, 通过三期遥感影像的直接对比分析, 获得了三江源地区草地退化空间数据集, 并在此 基础上分析了70 年代以来青海三江源地区草地退化的主要时空特征。结果表明: 三江源地区 草地退化是一个在空间格局上影响范围大, 在时间过程上持续时间长的连续变化过程。研究 发现, 三江源草地退化的格局在70 年代中后期已基本形成, 70 年代中后期至今, 草地的退 化过程一直在继续发生, 总体上不存在90 年代至今的草地退化急剧加强现象。草地退化的过 程在不同区域和地带有明显不同的表现, 如在湿润半湿润地带的草甸类草地上, 发生着草地 破碎化先导, 随后发生覆盖度持续降低, 最后形成黑土滩的退化过程; 在干旱、半干旱地带 的草原类草地上, 发生着覆盖度持续降低, 最后形成沙地和荒漠化草地的退化过程。三江源 地区草地退化具有明显的区域差异, 草地退化可以分为7 个区, 各区草地退化在类型、程度、 范围与时间过程方面具有明显不同的特点。     

黄河流域NDVI时空变化及其与降水/径流关系

NDVI是表征区域植被覆盖的重要指标。本文把黄河流域划分为 16个区域 ,利用Pathfinder (探路者 )的AVHRR NDVI资料 ,得到各区域 1982～ 1998年NDVI统计序列 ,详细分析了各区域NDVI时空变化特征。研究表明 ,17年来黄河流域各分区年平均NDVI都呈增加趋势 ,说明植被覆盖增加 ,生态环境好转 ,但是 8月份龙羊峡以上和兰河干流区间NDVI则有所下降 ,生态环境有局部恶化趋势。最后研究各区域NDVI与降水、径流和径流系数的年内、年际相关关系 ,结果表明 :从年内变化看 ,黄河流域各区域NDVI变化与降水、径流变化呈明显的正相关 ;从年际变化看 ,黄河流域各区域NDVI波动趋势与降水具有一定的相关性 ,但与径流、径流系数变化的关系相对复杂 ,不具有明显的相关性     

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。     

植被恢复工程对黄河中游12个典型流域水热平衡的影响研究

中国已成为全球植被迅速变绿贡献最大的国家,但植被变绿对水量平衡和能量收支平衡影响的相关研究有待加强。本文以植被恢复典型区域黄河中游12个流域为例,利用遥感植被指数NDVI和常规气象数据,基于布迪克假设和水热平衡指数（Water-Energy Ratio, WER）,分析了植被变绿的时空变化格局及其对水热平衡的影响。结果表明：① 傅抱璞模型中反映流域属性的参数w在12个流域的平均值为2.9,略大于模型的缺省值2.6。参数w与NDVI拟合的Pearson相关系数介于0.31~0.75,拟合性能较好。② 1982—2016年NDVI在12个流域均呈现显著增加趋势,尤其以植被恢复工程实施后更为显著（p<0.001）。相对1982—1999年,2000—2016年NDVI相对变化率在9.1%~17.5%之间,均值为12.9%,显著植被变绿已导致水热平衡向可利用水分减少、可利用能量增加方向转化。③ NDVI对WER变化的绝对贡献率达到77.5%,植被变绿已经成为黄河中游12个流域水热平衡变化的主导因素,其次为气候要素。植被的持续变绿带来了一些不利影响,植被恢复工程的生态效应研究有待进一步深入研究。     

宁夏植被覆盖动态变化及与气候因子的关系

利用1999-2009年的SPOT-VGT NDVI数据,计算出宁夏近11 a来的植被覆盖度,对其变化特征进行了研究,结合同期气象观测资料,从空间上分析了植被覆盖度与区域气候因子之间的关系。结果表明,南部六盘山区和北部引黄灌区植被覆盖度高,而中部干旱带等地区的植被覆盖度较低,但中部干旱带却有较高的绝对变化率;从时间变化来看,近11 a来宁夏大部分地区的植被覆盖度在逐年增加。植被覆盖度的变化与气候因子有关,除引黄灌区和六盘山林区外,中部干旱带等地的植被覆盖度与降水呈正相关,区域气候的干湿波动,影响了植被覆盖度的高低;在有灌溉保障条件的农业垦殖区,植被覆盖度还与气温呈正相关,即有效积温的增加,会促进农作物生长,从而导致区域植被的覆盖度提高。     

黄河流域植被覆盖度动态变化与降水的关系

利用8km分辨率Pathfinder NOAA-NDVI数据，对黄河流域1982－1999年地表植被覆盖的空间分布及时间序列变化进行了分析，并通过计算不同时段降水量与年最大NDVI之间的相关系数分析了降水对流域植被覆盖的影响。结果发现近20年来黄河流域平均植被覆盖度有增加趋势，但青藏高原上有所减小；汛期降水量的多少对地表植被覆盖度的年际变化起主要作用，其中草原地区影响最显著，而在森林植被区及部分灌溉农作区，降水的年际变化对地表覆盖的影响比较小。     

2001—2020年黄河流域植被覆盖变化及其影响因素

基于MODIS NDVI植被指数和气象数据集,以集合经验模态分解、趋势分析和随机森林回归分析等方法,分析了黄河流域2001—2020年植被覆盖时空变化特征,并对其气候驱动因素进行探讨。结果表明：（1）2001—2020年黄河流域植被覆盖整体呈显著增长趋势,增速为0.055/10a （P<0.05）,2010年之前增速（0.067/10a）大于2010年之后的增速（0.051/10a）。（2）空间上,植被覆盖增加区域主要分布在陕北黄土高原、甘肃省东南部、内蒙古自治区河套平原等退耕还林还草生态工程实施区域,而植被覆盖显著下降区域则集中在关中平原城市群、黄淮海平原以及青藏高原等区域。（3）气温、降水和CO₂浓度等对黄河流域植被生长起到正向促进作用,且绝对敏感性依次降低,而大气饱和水汽压差、太阳辐射等对植被生长起到抑制作用。本研究结果可为评估气候变化对黄河流域植被覆盖变化的综合影响提供参考依据。     

黄河头道拐—潼关区间植被恢复及其对水沙过程影响

黄河头道拐—潼关区间是黄河泥沙的主要来源区,也是中国植被恢复最快的地区。植被的快速恢复对径流和输沙过程产生了深远影响。本文基于250 m分辨率的归一化植被指数数据（MOD13Q1 NDVI）,使用统计分析和趋势分析技术,分析了头道拐—潼关区间不同景观单元植被恢复特点、影响因素以及其对水沙过程的影响,并对头道拐—潼关区间植被未来发展趋势进行了预测。研究结果显示：头道拐—潼关区间82.87%区域的植被呈显著增加趋势（p < 0.05）,且植被恢复速度最快的区域为半湿润的黄土丘陵沟壑区,坡度和降水量在不同景观单元下对植被恢复的影响不同。随着降水量的增加,头道拐—潼关区间NDVI和年降水量的相关性降低。在植被恢复背景下,黄河中游主要河流径流的主要影响因素仍然是降水量,输沙量同时受到降水量和植被恢复的影响,含沙量与NDVI呈现出较强的负相关关系,而与降水量的相关性较弱。随着植被覆盖度的增加,流域土壤侵蚀量降低,河流输沙量也呈降低趋势,土壤侵蚀量对河流输沙量的贡献率变化于39%~88%之间。基于植被恢复潜力和恢复速度,本文预测头道拐—潼关区间2020年、2030年、2040年以及2050年的NDVI平均值将分别达到0.68、0.75、0.79以及0.80。     

30年来青海三江源生态系统格局和空间结构动态变化

在多期遥感图像支持下,通过对生态系统类型进行辨识,获得了三江源地区生态系统类型空间分布数据集,并在此基础上分析了20世纪70年代中后期以来青海三江源地区生态系统格局和空间结构的动态变化。结果表明:30年来三江源地区生态系统格局稳定少动,生态系统类型变化相对缓慢,农田、森林、草地、水体与湿地和荒漠生态系统的年变化速率均小于0.5%,是长江、黄河流域乃至全国各区域生态系统转类变幅最小的稳定少动区。20世纪70年代中后期以来三江源地区生态系统类型的转变主要发生在草地和水体与湿地生态系统上,草地生态系统的变化主要发生在中部和东部地区,水体与湿地生态系统的变化主要发生在广大西部和北部地区。