近20年来黄河流域植被覆盖变化分析

利用1982～1999年AVHRR-NDVI数据和对应年份黄河流域气象观测数据，通过计算、分析春季、夏汛及伏秋黄河流域NDVI距平值和湿润指数距平值的年际变化，得出了20世纪80年代至90年代初黄河流域气候相对湿润，90年代中后期相对干旱，植被覆盖状况总体一直处于上升趋势的结论，并评估了黄河流域近20年来生态保护和建设工作成效。

The Vegetation Cover over Last 20 Years in Yellow River Basin

Vegetation cover is a major feature for ecological system. The change of vegetation cover in large area is mainly caused by climate and human activities. The Yellow River, the second largest river in China with a basin of 752,443 km2, includes semi-arid and arid environment. Therefore, it is necessary to study the change of vegetation cover in the Yellow River Basin, which will help us understand climate influences and impacts of human activities. In order to understand the change of vegetation cover in the Yellow River Basin and its influencing factors, we use the data of AVHRR-NDVI and the information of 76 meteorological stations in the Yellow River Basin covering 1982-1999 to analyze their spatial distribution and dynamic change in spring, summer and autumn. On the basis of calculating the NDVI mean deviation and Moisture Index (MI) mean deviation, we study the feature of MI mean deviation, the speed of NDVI mean deviation and the correlation between them. Finally, some conclusions are drawn. Firstly, the climate was relatively humid from 1982 to 1992 and relatively dry since 1993. The environment in the Yellow River Basin tended to be desiccated, but the vegetation cover is increasing. Secondly, the correlation between NDVI mean deviation and MI mean deviation demonstrates that the humid climate was helpful for vegetation cover. Thirdly, the average speed of vegetation cover increase was 0.58%. The speed of vegetation cover increase in the loess region and catchment area is 0-3.8%, which shows the achievement of ecological measurements in China. The vegetation cover in desert and riverhead region is decreasing, the speed of which is 0-3.0%, a reflection of the climate change.