基于SPOT—VGT的黄河流域植被覆盖时空演变

植被是土地覆盖中的最主要部分，是连接土壤、大气和生物等要素的自然“纽带”。植被覆盖动态变化对全球能量循环和物质循环具有重要影响，是全球变化研究的重要内容之一。黄河流域作为我国重要的粮食生产基地，其环境变化直接影响到流域经济的可持续发展。为了快速准确地提取地表植被状况，了解黄河流域生态环境，利用1998—2011年的SPOT-VGT遥感数据，结合地理信息技术，采用均值法和趋势分析法对黄河流域植被NDVI时空分布特征和变化趋势进行了动态监测。结果表明，（1）黄河流域14年NDVI均值的空间分布整体特征是东南部平原、盆地和西部山地植被状况要好于北部地区。其次，黄河流域属于干旱半干旱地区，植被发育主要依赖于水文条件，所以沿黄河干流和支流区域也具有较高的植被NDVI值。（2）黄河流域植被NDVl年均值近14年间整体呈缓慢增长趋势，1998--2000年呈现急剧减少态势，2001--2003年出现了较为快速的增长，2004--2011年又出现了较长时间的连续增长过程。（3）黄河流域植被NDVI基本不变的区域约占研究区总面积的71．13％；植被NDVI轻微改善的区域约占流域总面积的27．30％，且主要分布于流域东南部的盆地、平原和西部的山地、丘陵地区，植被NDVI退化的区域面积约占流域总面积的0．98％。黄河流域自1998年以来，植被NDVI整体在不断提高，生态环境在不断改善。

Spatio-temporal variation of vegetation cover based on SPOT-VGT in Yellow River Basin

Vegetation is one of the most important land covers on the earth, which is a bond of the soil, atmosphere and moisture. Vegetation dynamic change is a fundamental process that impacts on many parts of the environment and plays an important role on the study of ecology and environmental dynamics, so it is one of the core issues in global change research. Yellow River basin is an important grain production base in China and environmental change can affect the sustainable development of the basin economy. In order to understand the changes in vegetation coverage in Yellow River basin during 1998 and 2008, a combination of ancillary data and SPOT-VGT imagery data were interpreted to construct spatio-temporal distribution and change trend of vegetation cover in Yellow River basin from 1998 to 2011. Average method and slope of the linear regression were used to unravel spatial and temporal changes. The results show： （1） The region in southeastern part of Yellow River basin and western mountain has the higher NDVI of vegetation than northern region, and the surrounding region of main streams and tributaries of the Yellow River has also a higher NDVI values. （2） Vegetation Cover has a trend of slow increase in Yellow River Basin from 1998 to 2011, and prompted a rapid reduction of NDVI annual average from 1998 to 2000, rapid increase from 2001 to 2003, continuous growth from 2004 to 2011 respectively. （3） NDVI of vegetation overall presents the increasing tendency in Yellow River Basin between 1998 and 2011. Stable area with no change of vegetation accounts for about 71.13% of the study area; Area with minor improved of vegetation accounts for about 27.30% of the Yellow River Basin, and mainly distributes at basin, plain in southeast Yellow River basin and mountain, hills area in western part of the study area. Degraded area accounts for 0.98% of the total area. In short, vegetation was continually increasing, and environmental quality is improved in the Yellow River basin since 1998.