藏北高原植被物候时空动态变化的遥感监测研究

 利用遥感数据提取的植被物候格局及时空变化特征能很好地反映区域尺度上植被对全球变化的响应。目前关于青藏高原地区植被物候的少量报道基本上是基于物候站点的观测记录展开分析的。该文基于非对称高斯拟合算法重建了藏北高原2001–2010年的MODIS EVI (增强型植被指数)时间序列影像, 然后利用动态阈值法提取整个藏北高原2001–2010年植被覆盖的重要物候信息, 包括植被返青期、枯黄期与生长季长度, 分析了植被物候10年间平均状况的空间分异特征以及年际变化情
况, 并结合站点观测记录分析了气温和降水对植被物候变化的影响, 结果表明: (1)藏北高原植被返青期在空间上表现出从东南到西北逐渐推迟的水平地带性与东南高山峡谷区的垂直地带性相结合的特征, 近60%区域的植被返青期提前, 特别是高山地区; (2)植被枯黄期的年际变化不太明显, 大部分地区都表现为自然的年际波动; (3)生长季长度的时空变化特征由植被返青期和枯黄期二者决定, 但主要受返青期提前影响, 大部分地区生长季长度延长; (4)研究区内不同气候区划植被物候的年际变化以那曲高山谷地亚寒带半湿润区和青南高原亚寒带半干旱区的植被返青期提前和生长季延长程度最为明显; (5)基于气象台站数据分析气候变化对物候的影响发现, 返青期提前及生长季延长主要受气温升高的影响, 与降水的关系尚不明确。

Spatio-temporal variation of vegetation phenology in the Northern Tibetan Plateau as detected by MODIS remote sensing

Aim Estimating regional variation in vegetation phenology from time-series remote sensing data is important in global climate change studies. However, there are few studies on vegetation phenology for the Qinghai-Tibet Plateau and most are based on field records of stations.
Methods We utilized the dynamic threshold method to explore vegetation phenological metrics (greenup date, length of season and senescence date) of typical grassland in the Northern Tibetan Plateau. We used time-series TERRA/MODIS EVI data for 2001–2010 reconstructed by the asymmetric Gaussian function fitting method to analyze spatial pattern and differentiation of vegetation phenology and its inter-annual variation and to examine the relationship between phenological variation and climate changes.
Important findings The spatial pattern of date of vegetation greenup was embodied by transition from southeast to northwest and vertical zonation in the mountainous topography of the southeast. The vegetation greenup date in approximately sixty percent of the northern Tibetan Plateau had advanced, especially in high mountains. Interannual variation of vegetation senescence date was not obvious, and most of the region had natural inter-annual fluctuations. The variation of growing season length is influenced by greenup and senescence dates, but was chiefly affected by advanced greenup date lengthening the growing season. Among the four different climatic zones in the study area, the mountain and valley Nagqu sub-arctic and sub-humid zone and the southern Qinghai sub-arctic and semi-arid zone had the most apparent advanced greenup date and prolonged growing season. Based on measured data from weather stations, increased temperature appears to be a critical factor contributing to earlier greenup and prolonged growing season; however, the relationship between precipitation fluctuations and phenological variation was unclear.