青藏高原春季植被变化特征及其对夏季气温的影响

分析1982~2001年NDVI和青藏高原地区台站气温资料,得到结论:近20年来春季高原植被总体呈明显的增加趋势,其中以高原北部、西北部和南部日喀则附近地区的植被增加最明显。高原NDVI与季节同期和滞后的气温以正相关为主。春季NDVI与滞后0~3季气温都表现为正相关,尤以高原春季NDVI与夏季气温的相关更为显著。高原春季NDVI如果处于异常偏小(或偏大) 状态,同时高原的北部和中西部是较明显的NDVI负距平(或正距平)分布时,则高原地区夏季气温具有整体上(或大部分地区)偏低(或偏高)的倾向,平均气温和最高气温在高原西部和北部表现明显,对最低气温的影响的关键区位于高原的中南部和东南部。

Character of Spring Vegetation Change in the Qinghai-Tibet Plateau and Its Influence on Summer Air Temperature

Based on the monthly Normalized Difference Vegetation Index (NDVI) data that is made by GIMMS workgroup of NASA and the monthly air temperature data from 55 stations in the Qinghai-Tibet Plateau for the period of 1982 to 2001, the change characteristic of spring NDVI and the relationship between the spring NDVI anomaly and the summer air temperature have been studied by using the methods of Empirical Orthogonal Function (EOF), correlation analyse and Singular Value Decomposition (SVD). The results are summarized as follows: (1) Spring vegetation presents obviously increased direction over the Qinghai-Tibet Plateau, especially there are more obvious increase in the north and northwest of the plateau and the vicinity of Xigaz?. The mean and maximum air temperature are increased obviously in the north and northwest of the plateau, and the obvious area of minimum air temperature is located in the mid-east of the plateau. (2) The positive correlation between NDVI and air temperature lags 0 to 3 seasons. (3) The correlative coefficient spatial distribution between spring NDVI and summer mean temperature is consistent with its distribution between spring NDVI and maximal temperature. The obvious region of positive correlation is located in the west and northeast of the plateau. The spatial distribution of positive correlative coefficient between spring NDVI and summer minimal temperature is obvious in the northwest and southeast over the plateau. (4) The plateau summer air temperature has a close connection with the preceding spring NDVI. When spring NDVI is abnormally low (or high) over the plateau, and it is obvious negative (or positive) anomaly in the north and the mid-west of plateau, then the summer mean and maximum air temperature are low (or high) in the whole or great part of the plateau, especially obvious in the west and north of the plateau. The influence of spring NDVI on summer minimum air temperature presents consistent positive correlation in whole area, and the key area is located in the mid-south and southeast of the plateau.