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.%三江源,即长江、黄河和澜沧江源头区,其高寒生态系统的脆弱性和敏感性使其成为我国生态安全的重要屏障,在我国生态环境保护和建设方面处于重要地位.了解气候变化的影响对于全球气候变化背景下生态环境保护和恢复措施的实施至关重要.由于生态系统过程的复杂性、研究数据的可靠性以及模型本身的不确定性等,使得对高原植被生产力变化的驱动因素存在多种归因解释.本研究利用遥感-过程耦合模型(GLOPEM-CEVSA)估算三江源区2000–2012年植被净初级生产力,基于像元尺度的气温和降水为自变量的多元线性回归方法,分析在全球气候变化背景下,三江源区植被净初级生产力的时空分布格局,探讨气候水热因素对NPP的影响.研究结果表明:(1)模型模拟NPP与野外采样的地上生物量(AGB)显著线性相关,能够解释AGB空间变异的45％,高于MODIS生产力产品(MOD17A3)的解释能力(21％);(2)1990–2012年间三江源区的气候呈暖湿化趋势,较之1990–2000年,近10年气候呈暖湿化加速趋势;(3)在暖湿化气候变化背景下,三江源全区NPP的年际变化呈增加趋势(每10年增加13.7 g m–2),统计置信度为86％(即显著性水平P=0.14);三大流域对比表明,黄河源头NPP增速最快(17.44 g m–2(10 yr)–1,P=0.158),其次是长江源头,澜沧江增速最低(12.2 g m–2(10 yr)–1),统计置信度仅为67％;(4)NPP年际变化的气候因素分析发现,气温和降水能够解释全区草地NPP年际变异的83％,可解释全区高、中、低覆盖度草地NPP年际变异的78％、84％和83％.本研究结果表明气候变化在青藏高原高寒生态系统的植被生产年际变化趋势中起主导作用.这对认识全球气候变化对脆弱生态区的影响机制,及因地制宜地实施生态保护与恢复措施具有重要科学和现实指导意义.
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