Spatiotemporal Variation of Vegetation Coverage Index in North China during the Period from 1982 to 2006

In this paper,the spatiotemporal variation of normalized difference vegetation index(NDVI) values in north China was analyzed based on the GIMMS data during the period of 1982-2006.The preliminary results were as follows:(1) The average annual NDVI curves of vegetation were unidomal in north China.The NDVI peaks of vegetation occurred in summer,the NDVI peak in Beijing was the highest,then in Hebei Province,and it was the lowest in Inner Mongolia.The NDVI peak of forests was higher than that of grasslands and farmland;(2) In recent 25 years,the average annual NDVI in north China was increased.The average annual NDVI in Hebei Province was increased significantly,and the trend was the most significant(P0.01).The average annual NDVI in Beijing was also increased significantly.In different land cover types,the highest increase of average annual NDVI occurred over farmland,than over grasslands,and it was the slowest in forests;(3) Based on the spatial trend analysis,the proportion of NDVI increase in the study area was 15.96%,and that of NDVI decrease was 11.86%.In different provinces,the NDVI increase occurred mainly in Hebei Province,and the NDVI decrease occurred mainly in Inner Mongolia.In three land cover types,NDVI in farmland was increased more significantly than that in forests and grasslands;(4) Based on the background of warming and drying climate in north China,human activities were the main causes resulting in the NDVI variation.