1982~2011年北半球中纬度秋季植被绿度变化的主要模态

doi:10.13249/j.cnki.sgs.2014.010.1226

摘要/Abstract

摘要：

利用系统聚类方法和经验正交函数分解（EOF分析）2种方法,分别提取了北半球中纬度地区1982~2011年秋季（9~11月）归一化差值植被指数（NDVI）变化的主要模态,辨识了植被绿度变化的区域差异;并采用奇异值分解（SVD）的方法,综合时间和空间2个维度上的变异信息,揭示了植被绿度变化的气候背景。结果表明,北半球中纬度秋季植被绿度变化有2种基本模态,一种是持续增加模态（模态I）,该模态广泛分布于北美大陆、亚欧大陆的北半部（大约在55^oN以北）和东西两端,NDVI平均增速为0.014/10a;另一种是趋势转折模态（模态II）,NDVI先增加,后减少,转折点大致出现在1994年,该模态主要出现在亚欧大陆中部,NDVI变化的平均速率分别是0.027/10a和-0.017/10a,其中以40^oE~80^oE最为典型。植被绿度变化与温度变化的时空特征基本一致。模态I区域的温度变化以持续性升高为主要特征,模态II区域的温度变化则以先增加后降低为主要特征,转折年份与NDVI变化的转折年份基本一致。SVD分析的第一模态NDVI与温度的时间系数相关系数为0.82,第二模态为0.92。由此表明,植被绿度变化主导模态可能由温度变化模态所致,在区域-大洲尺度上,温度变化的区域差异导致了秋季植被绿度变化的区域差异。

关键词: 北半球, 植被绿度, 气候变化, 区域差异, 秋季

Abstract:

：To understand response of terrestrial ecosystem to climate changes, it is important to study variations in vegetation greenness (VG) under the changing climate. We firstly extend the Advanced Very High Resolution Radiameter (AVHRR)-based Normalized Difference Vegetation Index (NDVI) from 2006 to 2011 by calibrating the Moderate Resolution Imaging Spectroradiometer-based NDVI. Using hierarchical clustering and empirical orthogonal function (EOF) analysis, this study picked out main models of variations of autumn VG (September to November) which was indicate by NDVI from 1982 to 2011. Then, by using Singular Value Decomposition (SVD), we integrated temporal variations and spatial variations of NDVI and temperature to reveal climate background of variations in VG. We found that the MODIS-NDVI captures the main variations of VG as the AVHRR-NDVI; therefore, it is reliable to extend the AVHRR-NDVI with the MODIS-NDVI. Both of cluster analysis and EOF analysis show the variations in autumn VG had two main models. One (model I) was featured by an increasing trend of VG from 1982 to 2011. This model spreads across the North America land, northern part and (west, east) two ends of Eurasia. The mean rate of increase in NDVI was ~0.014 per decade. The other model (model II) was featured by turn of NDVI variations. This model mostly spread in the center area of Eurasia. The turn point of NDVI variations was about 1994. From 1982 to 1994, the NDVI increased at the rate of 0.027 per decade; while, from 1995 to 2011, the NDVI decreased at the rate of 0.017 per decade. EOF analysis as well as illustrates that above two models could explain 21.1% and 8.1% of total variations of NDVI, respectively. The SVD analysis illustrated that variations in NDVI matched well with variations in temperature. In the Model I area, the temperature changes were featured by an increasing trend. The time coefficients of NDVI and temperature had a strong correlation (R=0.82). In the model II area, the temperature changes were featured by a turn point. Before the turn point, temperature increased; after the turn point, temperature decreased. The time coefficients of NDVI and temperature also had a strong correlation (R=0.92). These results suggest that the persisting greening in the Model I area occurred in the climate warming background and conversion from greening to browning in the Model II area co-occurred with the climate changes from warming to cooling. These findings demonstrate that the main models of variations in VG might result from temperature variations. In the continental scale, the spatial heterogeneity of temperature variations resulted in spatial heterogeneity of VG variations.

Key words: North Hemisphere, vegetation greenness, climate changes, regional differences, autumn

中图分类号:

Q948

张学珍. 1982~2011年北半球中纬度秋季植被绿度变化的主要模态[J]. 地理科学, 2014, 34(10): 1226-1232.

Xue-zhen ZHANG. Main Models of Variations of Autumn Vegetation Greenness in the Mid-latitude of North Hemisphere in 1982-2011[J]. SCIENTIA GEOGRAPHICA SINICA, 2014, 34(10): 1226-1232.

图/表 4

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