2000—2012年黄土高原植被覆盖的时空变化

Spatial-Temporal Changes of Vegetation Restoration on Loess Plateau from 2000 to 2012

归一化植被指数(NDVI)是综合表征植被覆盖状况的重要指标之一。采用2000—2012年黄土高原1 km×1 km分辨率的MODIS NDVI影像数据,分析了退耕还林(草)工程实施以来黄土高原各省(区)、典型流域和土壤侵蚀类型区植被覆盖的时空变化特征,揭示了黄土高原退耕还林(草)措施的生态成效。结果表明:2000—2012年黄土高原植被覆盖整体呈增大趋势,且在时间和空间上有所差异。从空间尺度上看,黄土高原植被覆盖呈整体改善、局部退化趋势,植被覆盖增加了9.81%,尤以黄土丘陵沟壑区陕西省榆林、延安地区最为显著;从时间尺度上看,年际、春、夏、秋季NDVI呈增大趋势,冬季NDVI呈减小趋势;按省(区)来看,陕西省增幅最大(为0.47%),青海省增幅最小(为0.16%),山西、宁夏、甘肃、内蒙古分别增长0.38%、0.33%、0.31%、0.23%;按黄河中游典型流域来看,延河流域增幅最大(为1.14%),无定河流域次之(为0.59%),渭河流域增幅最小(为0.43%);按黄土高原侵蚀类型分区来看,水力侵蚀区植被覆盖增长率较大,风力侵蚀区则较小。NDVI增加主要发生在春、夏两季。

Normalized Difference Vegetation Index ( NDVI) is one of the important indicators of comprehensive characterization of vegetation coverage. Based on the MODIS NDVI data of Loess Plateau from 2000 to 2012, this study analyzed the spatial-temporal variability of vegetation coverage in the regions of the Loess Plateau, typical watersheds and types of soil erosion areas after the project of returning farmland to forests or grassland to show the effectiveness of ecological building. The results show that during the study period, the vegetation of the Loess Plateau shows an increscent tendency. However, there is an obvious spatial distribution between regions. In recent decade, the vegetation of the Loess Plateau increases to 9. 81%, especially in Yulin and Yan'an areas of Shaanxi in the loess hilly region is significant;the NDVI of inter-annual, spring, summer and autumn shows upward trend and winter's NDVI declines. For provinces, the largest rate with increasing trends of the vegetation accounting to 0. 47% is Shaanxi Province, the smallest accounting to 0. 16% is Qinghai Province. Later for Shanxi, Gansu, Ningxia and Inner Mongolia are 0. 38%, 0. 33%, 0. 31% and 0. 23% respectively. For typical basins, Yanhe River basin is increased the most to 1. 14%, followed by Wuding River with 0. 59%;Weihe River basin is only 0. 43%. Type of soil erosion, the increasing rate of vegetation coverage in water erosion area is faster while wind erosion area is not obvious. Meanwhile, NDVI incensement occurs mainly in spring and summer, accounting for more than 60% of the year.