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# Changing Spring Phenology Dates in the Three-Rivers Headwater Region of the Tibetan Plateau during 1960-2013

• The variation of the vegetation growing season in the Three-Rivers Headwater Region of the Tibetan Plateau has recently become a controversial topic. One issue is that the estimated local trend in the start of the vegetation growing season (SOS) based on remote sensing data is easily affected by outliers because this data series is short. In this study, we determine that the spring minimum temperature is the most influential factor for SOS. The significant negative linear relationship between the two variables in the region is evaluated using Moderate Resolution Imaging Spectroradiometer-Normalized Difference Vegetation Index data for 2000-13. We then reconstruct the SOS time series based on the temperature data for 1960-2013. The regional mean SOS shows an advancing trend of 1.42 d (10 yr)-1 during 1960-2013, with the SOS occurring on the 160th and 151st days in 1960 and 2013, respectively. The advancing trend enhances to 6.04 d (10 yr)-1 during the past 14 years. The spatiotemporal variations of the reconstructed SOS data are similar to those deduced from remote sensing data during the past 14 years. The latter exhibit an even larger regional mean trend of SOS [7.98 d (10 yr-1)] during 2000-13. The Arctic Oscillation is found to have significantly influenced the changing SOS, especially for the eastern part of the region, during 2000-13.
摘要: 近年来, 三江源植被春季物候期变化趋势的研究存在争议. 遥感数据的长度过短, 在反演植被生长季开始日（SOS）变化趋势时, 研究结果容易受到个别年份极端值的影响. 本文采用2000-2013年的MODIS-NDVI时序数列提取生长季开始日（SOS）, 并建立SOS与春季温度间的相关关系；再利用1960-2013年春季温度数据重建过去近五十年SOS的时间序列. 在五十年大背景下讨论SOS 近十年的变化, 结果表明：（1）春季最低温度是与三江源SOS相关性最高的气象因子. 1960-2013年间, 研究地区的SOS呈现显著提前趋势, 从1960年的160日提前到2013年的151日, 增长速率为1.42d/10a;（2）2000-2013年间, SOS提前速率加快, 增长至6.04 d/10a. 遥感反演结果与温度重建结果基本一致, 提前速率为7.98 d/10a;（3）北极涛动对三江源地区的SOS有显著影响, 尤其是在研究地区的东部.

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## Manuscript History

Manuscript revised: 09 June 2017
Manuscript accepted: 14 August 2017
###### 通讯作者: 陈斌, bchen63@163.com
• 1.

沈阳化工大学材料科学与工程学院 沈阳 110142

## Changing Spring Phenology Dates in the Three-Rivers Headwater Region of the Tibetan Plateau during 1960-2013

• 1. Key Laboratory of Regional Climate-Environment for East Asia, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
• 2. Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100107, China
• 3. University of Chinese Academy of Sciences, Beijing 100049, China

Abstract: The variation of the vegetation growing season in the Three-Rivers Headwater Region of the Tibetan Plateau has recently become a controversial topic. One issue is that the estimated local trend in the start of the vegetation growing season (SOS) based on remote sensing data is easily affected by outliers because this data series is short. In this study, we determine that the spring minimum temperature is the most influential factor for SOS. The significant negative linear relationship between the two variables in the region is evaluated using Moderate Resolution Imaging Spectroradiometer-Normalized Difference Vegetation Index data for 2000-13. We then reconstruct the SOS time series based on the temperature data for 1960-2013. The regional mean SOS shows an advancing trend of 1.42 d (10 yr)-1 during 1960-2013, with the SOS occurring on the 160th and 151st days in 1960 and 2013, respectively. The advancing trend enhances to 6.04 d (10 yr)-1 during the past 14 years. The spatiotemporal variations of the reconstructed SOS data are similar to those deduced from remote sensing data during the past 14 years. The latter exhibit an even larger regional mean trend of SOS [7.98 d (10 yr-1)] during 2000-13. The Arctic Oscillation is found to have significantly influenced the changing SOS, especially for the eastern part of the region, during 2000-13.

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