西藏雅鲁藏布江流域植物物候变化及其海拔效应

Changes in Vegetation Phenology and Its Elevation-Dependent Effects in the Yarlung Zangbo River Valley of Tibet,China

雅鲁藏布江流域位于青藏高原南部,海拔跨度较大,平均海拔4 600 m,是研究高海拔大流域气候变化生态响应的代表性区域。以雅鲁藏布江流域为例,综合运用1999—2013年的SPOT-VGT NDVI旬数据集和SRTM数字高程模型(DEM),利用阈值法提取物候特征,研究雅鲁藏布江流域植物物候变化及其海拔效应。结果表明,流域植物返青期提前的区域占流域总面积的61.3%,推迟的区域占38.7%;植物枯黄期提前的区域占45.3%,推迟的区域占54.7%。雅鲁藏布江流域植物生长季长度存在缩短现象,年变化率的像元平均值为-0.47 d·a-1。自下游至上游,流域植物返青期逐渐推迟,枯黄期逐渐提前,植物生长季长度总体上呈缩短趋势。随着海拔的增加,雅鲁藏布江流域植物生长季长度和年变化率总体上呈减小趋势。

The Yarlung Zangbo River Valley （Y ZR ） ,stretching across the southern part of the Tibetan Plateau from west to east over a wide range of elevation from 147 m to over 7 000 m above sea level （a .s . l .） with an average elevation of 4 600 m, has been regarded as one of the ideal regions for the study on ecological response to climate change in alpine water-shed. Based on the datasets of SPOT-VGT normalized difference vegetation index （NDVI） and SRTM digital elevation model （DEM） ,phonological features of the valley were extracted and elevation-dependent phenological change of the veg-etation of the YZR during 1999-2013 was analyzed. The SPOT-VGT NDVI was first preprocessed with the non-symmetri-cal Gaussian function （ AG） fitting method, and then the start date of growing season （ SOG） , the end date of the growing season （EOG） and the length of the growing season （LOG） of the vegetation was extracted, separately, through the threshold value method. Results show： （1 ） The SOG exhibited an advancing trend in 61. 3% of the YZR,and a delaying trend in 38. 8%,while the EOG did an advancing trend in 45. 3% and a delaying trend in 54. 7%. As a consequence,the LOG in the YZR was shortening,with the annual changing rate per pixel being -0 . 47 d^a 1 ; （2 ） The SOG was gradual-ly delaying, the EOG gradually advancing and the LOG gradually shortening along the river from the downstream up to theupstream. Besides,LOG and its annual changing rate is generally on a declining trend with rising elevation.