青藏高原典型草地NDVI时空演变的季节差异及其气候驱动

基于全球库存建模和制图研究(GIMMS)第三代归一化植被指数(NDVI3g)产品和气象数据，利用一元线性回归模型、偏相关分析和显著性T检验，分析了1982—2015年青藏高原高寒草甸和高寒草原春、夏、秋季NDVI时空演变的差异特征及其与气候因子的关系。研究表明：(1)高寒草甸春、夏、秋季NDVI整体均无明显变化趋势，高寒草原春季和夏季NDVI均显著增加，变化速率均为0.0002/a(P<0.05),而秋季NDVI变化趋势不明显。(2)空间上，高寒草甸春季NDVI显著增加面积占比31.95%,集中分布在祁连山区和三江源区，夏季NDVI显著增加的面积占比32.12%,主要分布在祁连山区、三江源地区和一江两河流域；秋季NDVI显著增加的比例为24.59%,集中分布于祁连山区和一江两河流域。高寒草原春、夏、秋季NDVI显著增加的区域均集中分布于西藏自治区北部和柴达木盆地南缘地区，分别占比44.20%、43.09%和37.99%。(3)高寒草甸春季和秋季NDVI均与气温显著正相关，偏相关系数达0.41(P<0.05)和0.23(P<0.05),夏季NDVI与气温、降水量和太阳辐...

Different spatiotemporal variations in seasonal NDVI and their climatic driving forces of a typical grassland on the Qinghai-Tibetan Plateau

Based on the third-generation normalized difference vegetation index (NDVI3g) of GIMMS and meteorological datasets, this study analyzed different spatiotemporal variations in NDVI and corresponding relationships to climate factors during spring, summer, and autumn in alpine meadow and alpine steppe biomes on the Qinghai-Tibetan Plateau in 1982-2015, combining a unary linear regression model with partial correlation analysis and a significance t-test. Results are as follows:(1) Generally, the NDVI of the alpine meadow biome exhibited no significant changing trends during spring, summer, and autumn; however, the NDVI of the alpine steppe biome increased significantly during spring and summer at a rate of 0.0002/a (P<0.05), while no obvious trends were observed during autumn. (2) Spatially, 31.95% of NDVI in the alpine meadow biome exhibited significant increasing trends during spring, mainly in areas distributed throughout the Qilian Mountains and the Three River Nature Reserve, and 32.12% during summer, mainly in areas distributed throughout the Qilian Mountains, the Three River Nature Reserve, and the Yarlung Zangbo River as well as the basins of its two tributaries, and 24.59% during autumn, mainly in areas distributed throughout the Qilian Mountains and the Yarlung Zangbo River as well as the basins of its two tributaries. The alpine steppe biome exhibited significantly increasing NDVI trends during spring (44.20%), summer (43.09%), and autumn (37.99%), mainly in areas distributed throughout the northern Tibet Autonomous Region and southern margin of the Qaidam Basin. (3) For the alpine meadow biome, the area-averaged NDVI exhibited a significantly positive correlation to temperature during spring and autumn, with partial correlation coefficients of 0.41 (P<0.05) and 0.23 (P<0.05), respectively. During summer, the NDVI of alpine meadow areas significantly correlated to temperature, precipitation, and solar radiation, for which partial correlation coefficients were 0.35 (P<0.01), 0.56 (P<0.01), and -0.57 (P<0.01), respectively. For the alpine steppe biome, we observed a significantly positive correlation between NDVI and temperature and precipitation during spring, with a higher partial correlation coefficient of 0.31 with precipitation (P<0.05). Significant correlations were also observed between the NDVI and temperature, precipitation, and solar radiation during summer, with a higher partial correlation coefficient of 0.46 with precipitation (P<0.01). Moreover, a significantly positive correlation between NDVI and solar radiation was observed during autumn. (4) Spatially, proportions of positive correlations between NDVI and temperature during spring and autumn in the alpine meadow biome were 76.50% and 67.86%, respectively, mainly distributed in areas within the Qilian Mountains and the Three Rivers Nature Reserve. Although 58.42% of alpine meadow areas exhibited positive correlations between NDVI and precipitation during summer, only 53.69% exhibited negative correlations between NDVI and solar radiation during autumn, both situated within the Qilian Mountains, headwaters of the Three Rivers Nature Reserve, and the Yarlung Zangbo River as well as the basins of its two tributaries. For the alpine steppe biome, proportions of positive correlations between NDVI and precipitation during spring and summer were 63.02% and 67.62%, respectively, primarily distributed within the western Tibet Autonomous Region and southern margin of the Qaidam Basin. This study provides a scientific basis for the protection of grassland resources and the management of plant-based carbon pools in alpine ecosystems, while also promoting a long-term increase in ecologically-based carbon sinks on the Qinghai-Tibetan Platea.