青藏高原中东部水热条件与NDVI的空间分布格局

Spatial variation of water/thermal elements and NDVI with altitudes in central and eastern Tibetan Plateau

青藏高原受大气环流和地势格局的共同作用，水热条件及植被空间分布呈现独特的三维地带性特征。但是青藏高原范围广、地势起伏大，水热条件及植被空间分布具有明显区域差异。本文利用青藏高原中东部100个气象站1982-2000年的降水、气温资料以及同期NO—AAAVHRR植被指数产品（NDVI），分析水热条件及植被的空间分布特征。首先，设置经向、纬向海拔渐变样带，考察海拔对水热条件及NDVI空间分布的影响；然后，按500米海拔间隔进行站点分组，分析约束了海拔高差后的经纬位置对水热条件及NDVI空间分布的影响。研究表明：在青藏高原中东部由于海拔高差大，热量条件分布首先受海拔递减规律控制，其次才表现出因太阳辐射差异的纬度地带性；而降水分布则主要受水汽通道位置和方向的影响，北上水汽和东部偏南走向山脉是研究区降水经向特征的主要成因；指示植被状况的年均NDVI，则受水热组合的控制，其分布格局是二者的叠加与综合。

Under joint effect of atmospheric circulation and topography, the distribution of water/thermal elements and vegetation bears a three-dimensional zonal characteristic in Tibetan Plateau. As we know, within the vast expanse of the Tibetan Plateau with undulating terrain, the spatial distribution of water/thermal elements and vegetation has strong local impressions, which are different in one location from the other. This paper aims to explore such a spatial pattern in central and eastern Tibetan Plateau, with ground collected data of air temperature and precipitation from 100 meteorological stations and remotely sensed NDVI data by NOAA AVHRR during 1982-2000. Firstly, latitudinal and longitudinal transects are designed to analyze the role of altitude in spatial distribution of water/ thermal elements. Secondly, to focus on roles of latitude and longitude in the above-mentioned spatial pattern,these 100 stations are divided into 5 groups with altitudes restricted nearly within a range of 500 m so as to restrain the influence of altitude. The study shows that 1） because of sharp altitudinal variation, the thermal element in the central and eastern Tibetan Plateau firstly follows the adiabatic lapse rate of air temperature while solar radiation variation over latitudes is the second thermal control factor; 2） the spatial distribution pattern of precipitation is relatively complex, which is dominated by the distance to and the accessibility of vapor sources; and 3）finally the annual mean NDVI, the indicator of general vegetation condition, is governed jointly by precipitation and accumulated air temperature, so its spatial variation is the combination of those of the two climate elements.