Spatial-temporal Changes Of Vegetation In Hebei Province Based On MODIS/NDVI And Its Affecting Factors

The research of vegetation index is an important part of research on vegetation coverage.Analysis of different vegetation type dynamic change and its relationship with the ecological factors is significant to the study of ecological environment change.Based on the technology of 3S and various mathematical methods,the author used MODIS/NDVI data and land-cover data of 2001-2010 time series in Hebei province,analyzed the spatial distribution and dynamic change characteristics of vegetation index.Calculate a decade of MODIS/NDVI data by tendency analysis method,anomaly vegetation index analysis,and partial correlation analysis.The average vegetation condition in the spatial distribution can be reflected from the average level of the vegetation index for many years.Besides,the time-space dynamic characteristics of vegetation index are studied in different regions,different elevation gradient and different vegetation types.The results showed that:(1)During the past 10 years,the annual change of the vegetation was slowly increasing in Hebei province,grew by 0.2%/10 a.The vegetation index in Jidong Region,Jizhong Region,Jibei Region and Jinan Region all had an increased trend,but the growth rate in Jizhong Region is lower than the growth rate in other partitions.There are significant spatial differences of vegetation index.The frequency of NDVI showed a unimodal structure.The area of vegetation increased was 74.41%,the area of vegetation decreased was 35.94% of the total area.There were large regional disparities in the vegetation growth,with the north and west doing well but the south and east deeply depressed,and the growth in Zhangjiakou and Cangzhou is better than other areas.The values of NDVI in different vegetation types are in the following sequence: broadleaf mixed forest > needle forest > shrub > farmland >grassland.The annual average trend of coniferous forest and wetlands changed significantly.(2)The analyzed results show that temperature was decreased in Hebei province in the last 10 years.The temperature in the Bashang region of Zhangjiakou and Chengde is low,and the temperature on Hebei plain is relatively high.The temperature in the east of Zhangjiakou,much of Tangshan and much of Chengde changed significantly,and trended down.The precipitation change was stable in Hebei province,and increased slowly.The climate in theBashang region of Zhangjiakou and Chengde was semiarid,and it is relatively humid in Qinhuangdao,Tangshan and the south of Hebei province.The precipitation in the Bashang region of Zhangjiakou and Chengde changed significantly,and trended down slowly.There is positive or negative partial correlation coefficient between NDVI and temperature in the 10 years.However,the relationship of partial correlation between NDVI and precipitation is positive.(3)The result suggested that the distribution of vegetation type certain correlated with the terrain,especially the height.Affected by the overall elevation in Hebei province,the correlation is not obvious.The vegetation index of broad-leaved forest,needle-leaved forest and farmland has certain negative correlation with the altitude,and the correlation is small.But there is a positive relativity between the vegetation index of Coniferous forest,shrubs and grass with the altitude.Apart from the effect by climate and topography,vegetation index dynamic change is subject to the interference from artificial disturbance.And the effect of implementing the environmental protection project would further complicate the research of vegetation coverage dynamic change.