黄土高原植被覆盖时空变化分析

Analysis of Spatiotemporal Variation of Vegetation Coveron the Loess Plateau

黄土高原是我国生态脆弱区之一,了解该地区植被覆盖时空变化对其生态恢复具有重要意义。本文基于MOD13A2数据集,利用Whittaker平滑法、Sen+Mann-Kendall检验的趋势分析方法及Hurst指数,对植被指数数据进行时序平滑以消除其不规则变化,并分析2001~2017年间黄土高原归一化植被指数数据序列的时空变化趋势及其稳定性特征,再进一步分析植被未来变化情况。结果显示:①研究区植被空间分布呈“东南高,西北低”特点,秦巴山区植被覆盖均值最高;年际间整体呈增加趋势,增速0.0086/a,黄土高原农业与草原生态区、燕山-太行山地区的植被增速较快。②从变化趋势看,植被变化呈现增加和减小趋势的像元占比分别为97.67%和2.33%,说明研究区植被覆盖在不断改善,降低趋势地区集中分布于汾渭盆地、秦巴山地地区。③研究区Hurst整体均值0.286,黄土高原整体及各生态区均以反向变化特征(Hurst<0.5)为主,持续性特征地区主要分布于黄土高原西北及南部两侧。④结合趋势分析及Hurst指数,研究区及各生态区植被未来将由改善趋势转变为退化趋势(89.78%),内蒙古高原中部荒漠区植被持续改善趋势面积占比较高,汾渭盆地和秦巴山区的持续退化特征较明显。

The Loess Plateau is one of the ecologically fragile areas in China,and it is of great significance to understand the temporal and spatial changes of vegetation cover in this area for its ecological restoration.Based on the MOD13A2 dataset,this paper used the Whittaker smoothing method,the trend analysis method of Sen+Mann-Kendall test and the Hurst index to smooth the vegetation index data to eliminate its irregular changes,and analyzed the temporal and spatial variation trends and stability characteristics of the normalized vegetation index data series on the Loess Plateau during 2001~2017,and then further analyzed the future changes of vegetation.The results showed that:(1)The spatial distribution of vegetation in the study area was"high in the southeast and low in the northwest",and the average vegetation cover in the Qinba Mountains was the highest.The overall inter-annual growth rate was 0.0086/a,and the vegetation growth rate in the agricultural and grassland ecological region of the Loess Plateau and the Yanshan-Taihang Mountains was relatively fast.(2)From the perspective of change trend,the proportion of pixels showing an increasing and decreasing trend of vegetation change was 97.67%and 2.33%,respectively,indicating that the vegetation cover in the study area was continuously improving,and the decreasing trend areas were concentrated in the Fenwei Basin and Qinba Mountains.(3)The overall mean value of Hurst in the study area was 0.286,and the overall and ecological regions of the Loess Plateau were dominated by the reverse change characteristics(Hurst<0.5),and the persistent characteristics were mainly distributed in the northwest and south of the Loess Plateau.(4)Combined with the trend analysis and Hurst index,the vegetation in the study area and each ecological region will change from an improvement trend to a degradation trend in the future(89.78%),and the area of vegetation continuous improvement trend in the desert area of the central Inner Mongolia Plateau is relatively high,and the continuous degradation characteristics of the Fenwei Basin and Qinba Mountains are more obvious.