2000-2015年青藏高原草地归一化植被指数对降水变化的响应

Responses of normalized difference vegetation index( NDVI) to precipitation changes on the grassland of Tibetan Plateau from 2000 to 2015

降水变化是造成青藏高原草地植被生长年际变异的重要因素,降水量、分配方式及发生时间是降水变化的重要特征.利用2000—2015年青藏高原及附近区域145个气象站点的降水资料,以年降水量表征降水整体状况,以改进的降水集度(PCI)表征年内降水的分配状况,以定义的降水重心(PC)表征降水的集中时期,分析青藏高原降水变化的时空特征;并进一步以归一化植被指数最大值(NDVI_(max))表征植被生长状况,探讨了青藏高原草地对降水年际变化的响应.结果表明:青藏高原年降水量和PCI存在明显的梯度特征,PC在西藏南部形成中心.青藏高原灌丛草地NDVI_(max)年际变化对PCI变化响应敏感,降水越均匀越有利于NDVI_(max)的增加,但受到降水量的限制;高寒草甸对降水特征没有表现出显著的相关关系;草原植被NDVI_(max)的年际变化同时受PCI和PC的控制;高寒荒漠植被NDVI_(max)的年际变化主要受降水量的控制.在研究降水变化对青藏高原不同类型植被的影响时,除降水量之外,还需进一步考虑降水的分配格局等特征.

Precipitation change is an important factor in the inter-annual variation of grassland growth on the Tibetan Plateau. The total amount, distribution pattern and concentration time are three basic characteristics of precipitation change. The temporal and spatial characteristics of precipitation change were analyzed based on climate data of 145 meteorological stations on the Tibetan Plateau and nearby areas from 2000 to 2015. The total precipitation amount was characterized by annual precipitation, distribution pattern of precipitation during the year was characterized by improved precipitation concentration index （PCI）, and precipitation centroid （PC） was defined to indicate the change in precipitation concentrated time. To better illustrate the response of grassland to precipitation change, vegetation growth status was characterized by the maximum value of normalized difference vegetation index （NDVImax）. Results indicated that the annual precipitation and PCI had an apparent gradient across the whole plateau and the latest PC occurred in the southern plateau. NDVImax of alpine shrub grassland was significantly correlated with the change of PCI,increased with even distribution of precipitation during growth period, and limited by the total annual precipitation. Alpine meadow did not show significantly correlations with these three indices. The inter-annual variability of NDVImax of steppe was controlled by both PCI and PC. NDVImax of alpine desert grassland was mainly controlled by annual precipitation. In addition to annual total amount of precipitation, the distribution characteristics of precipitation should be further considered when the influence of precipitation change on different types of vegetation on the Qinghai Tibet Plateau was studied.