The vegetation ecosystem of the Qinghai-Tibet Plateau in China, considered to be the ′′natural laboratory′′ of climate change in the world, has undergone profound changes under the stress of global change. Herein, we analyzed and discussed the spatial-temporal change patterns and the driving mechanisms of net primary productivity (NPP) in the Qinghai-Tibet Plateau from 2000 to 2015 based on the gravity center and correlation coefficient models. Subsequently, we quantitatively distinguished the relative effects of climate change (such as precipitation, temperature and evapotranspiration) and human activities (such as grazing and ecological construction) on the NPP changes using scenario analysis and Miami model based on the MOD17A3 and meteorological data. The average annual NPP in the Qinghai-Tibet Plateau showed a decreasing trend from the southeast to the northwest during 2000-2015. With respect to the inter-annual changes, the average annual NPP exhibited a fluctuating upward trend from 2000 to 2015, with a steep increase observed in 2005 and a high fluctuation observed from 2005 to 2015. In the Qinghai-Tibet Plateau, the regions with the increase in NPP (change rate higher than 10%) were mainly concentrated in the Three-River Source Region, the northern Hengduan Mountains, the middle and lower reaches of the Yarlung Zangbo River, and the eastern parts of the North Tibet Plateau, whereas the regions with the decrease in NPP (change rate lower than -10%) were mainly concentrated in the upper reaches of the Yarlung Zangbo River and the Ali Plateau. The gravity center of NPP in the Qinghai-Tibet Plateau has moved southwestward during 2000-2015, indicating that the increment and growth rate of NPP in the southwestern part is greater than those of NPP in the northeastern part. Further, a significant correlation was observed between NPP and climate factors in the Qinghai-Tibet Plateau. The regions exhibiting a significant correlation between NPP and precipitation were mainly located in the central and eastern Qinghai-Tibet Plateau, and the regions exhibiting a significant correlation between NPP and temperature were mainly located in the southern and eastern Qinghai-Tibet Plateau. Furthermore, the relative effects of climate change and human activities on the NPP changes in the Qinghai-Tibet Plateau exhibited significant spatial differences in three types of zones, i.e., the climate change-dominant zone, the human activity-dominant zone, and the climate change and human activity interaction zone. These research results can provide theoretical and methodological supports to reveal the driving mechanisms of the regional ecosystems to the global change in the Qinghai-Tibet Plateau.

植被净初级生产力(net primary productivity, NPP)在全球气候变化及碳循环研究中扮演着重要的角色,精准快速的估算NPP对评估区域生态系统承载力以及合理利用自然资源具有重要的意义。利用2011-2014年甘南地面实测草地地上生物量(aboveground biomass, AGB)数据和根冠比系数计算的草地NPP数据,分别验证了MOD17A3 NPP产品和基于CASA(Carnegie-Ames-Stanford approach)模型估算的草地NPP的精度,分析了2000-2016年甘南地区草地NPP的时空动态变化。结果表明:基于CASA模型模拟的草地NPP精度整体上高于MOD17A3 NPP产品的精度,其均方根误差(root mean square error, RMSE)较MOD17A3 NPP小9.94 g C·m^-2;CASA模型分析的甘南地区草地NPP总体上呈现由西南向东北逐渐减少的趋势;对不同草地类型而言,沼泽类的平均NPP最高(469.07 g C·m^-2),温性草原类最低(324.18 g C·m^-2),而占研究区草地总面积比例较大的高寒草甸类和高寒灌丛草甸类草地的平均NPP分别为449.22和465.27 g C·m^-2;2000-2016年间,甘南地区大部分草地NPP稳定不变,其面积占研究区草地总面积的75.31%,NPP呈增加趋势的区域占草地面积的22.63%,而NPP呈减少趋势的区域占比最小,仅为2.06%。以上研究结果表明CASA模型在高寒地区草地NPP评估、草地资源合理利用与管理方面具有重要的应用价值。

Net primary productivity (NPP) plays an important role in global carbon cycle and is important to understanding drivers of climate changes. Precise and rapid estimation of vegetation NPP is important for evaluating ecological carrying capacity at a regional scale and managing natural resources reasonably. In this study, field-measured grassland above ground biomass (AGB) from 2011 to 2014, MODIS remote sensing data and meteorological data in Gannan prefecture were used. In combination with the ratio of belowground biomass to AGB, we calculate the grassland NPP, and evaluate the accuracy of the MOD17A3 product and Carnegie-Ames-Stanford approach (CASA) model, and analyze the dynamic changes of grassland NPP from 2000 to 2016 using the better method. The results show that the accuracy of grassland NPP predictions from the CASA model (root mean square error (RMSE) = 9.94 g C ·m^-2·yr^-1) is higher than that of MOD17A3 product. The average annual grassland NPP determined by the CASA model shows a decreasing trend from the southwest to northeast between 2000 and 2016 in our study area. Comparing different vegetation types, the annual NPP for marsh grassland (469.07 g C ·m^-2·yr^-1) was the highest, while that of temperate steppe grassland was the lowest (324.18 g C ·m^-2·yr^-1). In addition, the annual NPP of alpine meadow and alpine shrub meadow grasslands (which have relatively large area in Gannan prefecture) was, respectively, 370 and 430 g C ·m^-2·yr^-1. Over the past 17 years, the annual grassland NPP was generally stable in most regions, (75.31% of the total grassland area). Meanwhile, an increasing NPP trend was seen in 22.63%, and a decreasing trend in just 2.06% of the Gannan prefecture area. These results suggest that the CASA model has an important role in grassland NPP estimation and will assist in the sustainable management of grassland resources in alpine areas.

基于2000年以来塔里木河下游生态输水资料、气象数据、土地利用/覆被变化数据等,结合修正的CASA（Carnegie-Ames-Stanford approach）模型和土壤微生物呼吸模型（Heterotrophic respiration,R_H）估算了2001—2019年植被净生态系统生产力（Net ecosysterm productivity,NEP）,分析了植被碳源/汇空间分布变化,探讨了塔里木河下游生态输水对植被碳源/汇变化的影响。结果表明：（1） 随着2000年以来塔里木河下游生态输水,下游退化的生态系统有一定程度的恢复,植被碳汇区域呈现扩大的趋势。2001—2019年NEP以0.541 g C·m^-2·a^-1的速率呈现上升趋势,其中夏季增加速率最大,为0.406 g C·m^-2·a^-1,增加的区域主要位于大西海子水库北部、英苏、博孜库勒湿地、喀尔达依湿地以及台特玛湖。碳汇面积从2001年的71 km²增加至2019年的355 km²,增加了4倍。（2） 在季节变化上,夏季碳汇面积为109 km²,在四季中占比最大,春秋次之,冬季无明显碳汇面积。（3） 塔里木河下游生态系统碳汇面积变化次序为：草地>林地>耕地>未利用地>水域>建设用地。此外,林地和草地年平均变化率最高,分别为2.69 km²·a^-1和3.57 km²·a^-1。生态输水量与碳汇面积有很好的线性关系,碳汇面积变化存在约1 a的滞后效应。

The net ecosystem productivity (NEP) of vegetation in the lower reaches of Tarim River, Xinjiang, China from the year 2000 was estimated using data of ecological water conveyance, meteorology, land use/cover changes combined with the modified Carnegie-Ames-Stanford approach (CASA) mode and soil microbial respiration models (R_H). The spatial distribution of vegetation carbon sources/sinks was analyzed, and the effect of ecological water conveyance on changes in these sources/sinks in the lower reaches of Tarim River was discussed. Results showed that (1) ecological water conveyance to the lower reaches of Tarim River since 2000 has allowed the degraded ecosystem in this area to recover to a certain extent. In addition, the vegetation carbon sinks in the area showed an increasing trend. Specifically, from 2001 to 2019, NEP showed an increase rate of 0.541 g C·m^-2·a^-1. The maximum increase rate, which was 0.406 g C·m^-2·a^-1, was observed in summer. The areas in which the carbon sinks increased were mainly located in northern Daxihaizi Reservoir, Yingsu, Bozikule Wetland, Kaldayi Wetland, and Taitma Lake. The area of vegetation carbon sinks increased by four times from 71 km² in 2001 to 355 km² in 2019. (2) In terms of seasonal variation, the carbon sink area measured 109 km² in summer. Indeed, this season contributed the largest to the total carbon sink area among the four seasons, followed by spring and autumn. No obvious carbon sink areas were noted in winter. (3) Changes in the total carbon sink area of different ecosystems showed the order grassland>woodland>cultivated land>unused land>water area>construction land. The annual average change rates of the carbon sink areas in woodland and grassland, at 2.69 km²·a^-1 and 3.57 km²·a^-1, respectively, were higher than those of any of the other ecosystems. A good linear relationship between ecological water conveyance and carbon sink area was observed, and changes in carbon sink area indicated a lag effect of approximately 1 year.

水是西北地区可持续发展的生命线,中国西北地区占国土总面积35.9%,水资源约占全国水资源总量的5.7%。从水文气象、生态景观与社会经济的演变角度,面向水资源优化配置、生态环境与社会经济协调发展,探索提出西北“水三线”的划分格局,即“胡焕庸线”“阳关线”和“奇策线”。“水三线”是西北水资源合理开发利用的优化配置线、西北生态文明与环境保护的特征分区线、“一带一路”建设的战略制导线和边疆长治久安、社会稳定的国家安全线。针对西北地区水资源开发利用存在的问题、面临的挑战以及西北稳定发展的地理与历史之忧,本文通过对西北调水方案的初步分析,提出了西北“水三线”建设的空间格局与水资源配置方略,即通过建设南水北调大西线这一重大的基础工程,跨越“胡焕庸线”,促进中国东西部地区间适度均衡发展;跨越“阳关线”,促进河西走廊社会经济发展;跨越“奇策线”,增强新疆水资源及环境承载能力,建设和谐美丽、长治久安的西北边疆,形成以西北“水三线”建设为构架的水资源梯度配置格局,支撑西北地区经济社会稳定发展、生态文明建设,促进国土资源、人口分布、产业经济的空间均衡、优化布局、协调发展,为“一带一路”建设提供水资源保障。

中国西北地区长期面临资源组合不匹配、区域发展不平衡的问题,而空间区位又决定了其具备促进区域协调、沟通国际国内、调整经济结构、筑牢生态屏障的战略地位。建设具有引领作用的生态经济枢纽区,将有助于改善西北及全国的生态环境问题、提升全域生态安全水平,同时也对国家经济发展具有推动作用。本文立足中国西北“水三线”空间格局,依据国家战略定位与生态经济功能,基于对研究区人地环境、城市群与城镇发展体系、人口布局与民族构成的全面解析,解读生态经济枢纽区的基本内涵,其可归纳为生态功能区、经济枢纽区、文化融生区、深陆通道区四个方面。进一步,本文综合宏观布局、资源禀赋、生态环境、陆海统筹等视角,阐明了生态经济枢纽区建设的功能定位,构建了西北“水三线”地区极点带动、轴带支撑的总体空间布局。并提出河西、兰西、天山北坡、环塔里木盆地绿洲四大生态经济枢纽区的建设格局与发展途径,探索了生态经济枢纽区与国家战略布局的互动关系。以期助力中国新时期西部大开发形成新格局,为中国“一带一路”的“深陆”研究提供科学依据。

Water shortage, unmatched combination of resources and unbalanced regional development are acute problems in northwest China. This region has a strategic location in promoting coordinated regional development, communicating international and domestic markets, adjusting economic structure and building ecological barriers. Therefore, the construction of eco-economic pivotal zones in northwest China would contribute to relieving the eco-environmental dilemma and improving the level of regional ecological security, which has a positive influence on the national economic development. Based on the analysis of human-environment interaction, urban agglomeration and development system, population distribution and ethnic composition in northwest China under the "Three Water Lines" pattern, this study firstly interprets the basic connotation of the eco-economic pivotal zones in this region. We propose that the eco-economic pivotal zone is a strategic area for national and global man-land coordination, which could be defined from the perspectives of ecological function zone, economic hub zone, cultural integration zone and deep-land passage zone. Based on the needs of national macro-strategic layout and land-sea coordination, we clarify the multi-functional orientations of eco-economic pivotal zones. Furthermore, this paper constructs a comprehensive development pattern in northwest China under "Three Water Lines" strategy, which is composed of 9 urban growth poles, 71 city nodes, 4 development axes and 4 eco-economic pivotal zones. And the construction layout as well as the development paths of Hexi, Lanzhou-Xining, north slope of Tianshan Mountains and circum-Tarim Basin eco-economic pivotal zones are also proposed. Finally, this paper discusses the interactive mode between the eco-economic pivotal zones and China's national development strategy layout, which would help the formation of a new pattern of development in western China, and provide a scientific basis for a better understanding of the Belt and Road Initiative.

该文在综合分析已有光能利用率模型的基础上，构建了一个净初级生产力(NPP)遥感估算模型，该模型体现了3方面的特色：1)将植被覆盖分类引入模型，并考虑植被覆盖分类精度对 NPP 估算的影响，由它们共同决定不同植被覆盖类型的归一化植被指数(NDVI)最大值；2)根据误差最小的原则，利用中国的NPP实测数据，模拟出各植被类型的最大光能利用率，使之更符合中国的实际情况；3)根据区域蒸散模型来模拟水分胁迫因子，与土壤水分子模型相比，这在一定程度上对有关参数实行了简化，使其实际的可操作性得到加强。模拟结果表明，1989～1993年中国陆地植被NPP平均值为3.12 Pg C (1 Pg=10¹⁵ g)，NPP模拟值与观测值比较接近，690个实测点的平均相对误差为4.5%；进一步与其它模型模拟结果以及前人研究结果的比较表明，该文所构建的NPP遥感估算模型具有一定的可靠性，说明在区域及全球尺度上，利用地 理信息系统技术将遥感数据和各种观测数据集成在一起，并对NPP模型进行参数校正， 基本上可以实现全球范围不同生态系统NPP的动态监测。

本文以MOD17A3HGF植被净初级生产力(NPP)数据为基础,结合气温、降水及DEM数据,开展了2000-2020年黄河流域植被NPP时空变化特征及其对水热条件和退耕还林还草工程实施的响应研究。结果表明:①黄河流域植被NPP总体呈显著线性增加趋势 (P25°和<15°区域,反映出退耕还林还草工程的实施对黄河流域中部黄土高原地区的植被改善具有一定的作用。

On the basis of MOD17A3HGF vegetation primary productivity (NPP) data, as well as the air temperature, precipitation and DEM data, the temporal and spatial change characteristics of vegetation NPP in the Yellow River basin from 2000 to 2020 and its response to hydrothermal and grain for green project (GGP) is carried out. The results show that: ① the overall trend of vegetation NPP in the Yellow River basin shows a significant linear increase (P<0.001), and the growth rate of vegetation NPP in the middle reaches is higher than that in the lower reaches, and the lower reaches is higher than the upper reaches. The vegetation NPP in the Yellow River basin increase significantly, accounting for 95.29%, which is concentrate in the middle reaches (the Loess Plateau region), while the significantly decrease areas are mainly concentrated in densely populated urban areas. ② The vegetation NPP in the Yellow River basin is mainly positively correlated with the annual average air temperature and annual precipitation, of which the significant positive correlations account for 11.15% and 42.35%, respectively, and which distribute in east-west and south-north direction, respectively. ③ The growth of vegetation NPP in the slope of [15°,25°] region is the fastest, followed by the >25° and <15° regions. It reflects the vegetation improvement effect of the grain for green project on the Loess Plateau in the middle reaches of the Yellow River basin.

大别山区作为红色革命老区,为秉承绿色发展理念,在大力发展经济的同时,对生态环境的研究尤为重要。以植被净初级生产力(NPP)为研究点,利用2000—2018年间的遥感和气象等数据,利用改进的CASA模型对研究区植被NPP进行估算,并分析讨论植被NPP的变化趋势及其对气候变化的响应。研究结果表明:①2000年以来大别山区整体NPP主要集中在400~600 gC/(m²·a)之间,整体植被NPP缓慢上升,整体涨幅为24.16%;②研究区NPP与气象因子相关,从整体来看气温与NPP相关性最高(R²=0.79,P<0.05),其次为太阳辐射(R²=0.70,P<0.05),降水与NPP相关性最低(R²=0.51,P<0.05);③土地利用/覆盖变化引起的NPP总增加量为6.23×10^-2 TgC,主要是由于耕地转化为林地引起的;④研究区的NPP未来变化趋势主要以持续增加为主。

为研究京津冀植被NPP的时空变化,选用MOD17A3数据,采用一元线性回归分析对京津冀地区2000—2019年植被NPP在20 a间的时空演变进行分析,并对NPP与气候因子的相关关系进行分析。结果表明:京津冀地区植被NPP主要集中在200~400 gC/(m²·a),2000—2019年京津冀植被NPP平均值和最大值在稳定的基础上缓慢上升,其中NPP最大值和平均值的峰值都出现在2016年,分别为908.40 gC/(m²·a)和385.10 gC/(m²·a);2000—2019年京津冀植被NPP增长的区域占整个研究区域的97.12%,NPP降低的区域多出现在城市周围;2000—2019年京津冀地区4种植被覆盖类型按NPP均值从小到大排列依次为:农田、灌丛、草地、森林;从稳定性上看,2000—2019年京津冀NPP的稳定性表现为高低波动并存,并以较低波动为主;京津冀地区NPP与年均气温呈低度相关性,与年降水呈高度相关性。研究成果可为京津冀地区的生态文明建设、生态环境修复及治理保护提供参考依据。

Net primary productivity (NPP) is recognized as an important index of ecosystem conditions and a key variable of the terrestrial carbon cycle. It also represents the comprehensive effects of climate change and anthropogenic activity on terrestrial vegetation. In this study, the temporal-spatial pattern of NPP for the period 2001–2012 was analyzed using a remote sensing-based carbon model (i.e., the Carnegie-Ames-Stanford Approach, CASA) in addition to other methods, such as linear trend analysis, standard deviation, and the Hurst index. Temporally, NPP showed a significant increasing trend for the arid region of Northwest China (ARNC), with an annual increase of 2.327 g C. Maximum and minimum productivity values appeared in July and December, respectively. Spatially, the NPP was relatively stable in the temperate and warm-temperate desert regions of Northwest China, while temporally, it showed an increasing trend. However, some attention should be given to the northwestern warm-temperate desert region, where there is severe continuous degradation and only a slight improvement trend.

中国西北地区MOD17A3 NPP数据产品缺失严重，影响了该区域植被净初级生产力的进一步研究。本研究利用气象数据、高程数据、NDVI和质量好的MOD17A3 NPP，构建BP神经网络模型，模拟2000&mdash;2014年西北地区植被NPP，填补数据缺失区域。利用一元线性回归分析法、R/S分析法、偏相关分析法等，分析了植被NPP的时空变化特征及其与气象要素的关系。结果表明：（1）MODIS NPP产品值与BP神经网络模拟值的决定系数R²、平均绝对误差MAE、平均相对误差MRE、均方根误差RMSE分别在0.833～0.906、25.84～40.10、0.16～0.23和34.57～59.36，满足精度要求，BP神经网络模型适用于模拟西北地区植被NPP。（2）植被年均NPP具有较强的空间差异，呈现出由东南向西北递减，而新疆西北部地区出现&ldquo;条块状&rdquo;高值区特征。（3）2000&mdash;2014年西北地区植被年均NPP在106.64～156.17 g C&middot;m^-2&middot;a^-1，年际变化上呈现波动下降趋势。（4）2000&mdash;2014年西北地区植被NPP变化具有空间异质性，以减少为主，仅10.79%的区域通过了显著性检验。植被NPP变化具有较弱的持续性特征，未来发展方向以不确定为主，有利和不利为辅，其中有利区域面积大于不利区域。（5）植被NPP对气温和降水的响应具有空间差异，总体上与降水关系更密切。

The data production of MOD17A3 NPP in northwest China is seriously deficient, with consequences on further research on vegetation net primary productivity (NPP) in this region. Based on the meteorological data, DEM, NDVI, and MOD17A3 NPP with high quality, the BP neural network model was constructed to simulate vegetation NPP and fill the areas without NPP data in northwest China from 2000 to 2014. Its spatio-temporal variations and relationships with meteorological factors were analyzed using unitary linear regression, R/S analysis, and partial correlation analysis. The results showed that: (1) Coefficients of determination (<em>R</em>²), mean absolute error (MAE), mean relative error (MRE) and root mean square error (RMSE) between MODIS NPP and simulated NPP were 0.833-0.906, 25.84-40.1, 0.16-0.23, 34.57-59.36, respectively, which well met the accuracy requirements. The BP neural network model was suitable for vegetation NPP simulation in northwest China. (2) The annual mean NPP had a strong spatial variation, showing a gradual decline from southeast to northwest and a high-value block area in the northwest of Xinjiang. (3) The annual mean NPP ranged between 106.64 and 156.17 g C&middot;m^-2&middot;a^-1 from 2000 to 2014, with a slightly fluctuating downward trend in the interannual variation. (4) From 2000 to 2014, the change of NPP in northwest China had spatial heterogeneity, which was mainly reduced. Only 10.79% of the areas passed the significance test. NPP change was weakly persistent. The future change trend of NPP is mainly uncertain, supplemented by improved and declined areas, with the improved area being larger than the declined area. (5) Responses of vegetation NPP to temperature and precipitation varied spatially, which were generally more closely related to precipitation.