The Study On NDVI Temporal And Spatial Change And Driving Factors In Yulin

In this paper, Yulin as the research object, 2000-2011 years of MODIS NDVI images whose spatial resolution is 250 m. we need to make the projection transformation and extract the normalized difference vegetation index(NDVI),then take band operation, maximize synthesis, time series analysis, linear regression analysis to study change difference of NDVI from different dimension of Yulin region. we select DEM data of 30 meters resolution and precipitation and evaporation data of 27 meteorological station of counties(districts) and surrounding of Yulin,then make quantitative analysis between elevation, slope, climatic factors(precipitation and evaporation) and NDVI.we can draw the following conclusions:1.From the time point of view, in the past 15 years vegetation grew well in Yulin, normalized difference vegetation index(NDVI) increased significantly, which is also consistent with the timeliness of national policy of returning farmland to forest since 1999.(1) from the perspective on the season, the change of vegetation index(NDVI) of four seasons were obvious, vegetation index rank can reflect: summer > autumn > spring > winter;(2) from the point of years change, the fluctuation rules of vegetation NDVI of Yulin show an unimodal type curve that changing with the seasons changes, through the process of first rise after the fall.(3)Interannual variability : 2000-2002 largest rise in NDVI, 2002-2004 and 2006-2012 is the stable growth phase, 20012-2014, NDVI growth is slowing but still keep growing.2.From the space point of view, yulin vegetation NDVI significantly increased from 2000 to 2014, and has obvious regional differences.on the whole, it shows the trend of "east high west low, south high north low", largely to desertification line(the ancient Great Wall) as the boundary, can be shown as: the loess gully area > sand savanes.3.Yulin counties(districts) of vegetation index(NDVI) is characterized by obvious space difference: the eastern counties(districts)(Wubao, Qingjian, Suide, Zizhou, Mizhi) were significantly higher than those in the west counties(districts)(Shenmu, Yuyang, Hengshan,Dingbian and so on).Yulin vegetation NDVI increased significantly in 2000-2014,which reflects the vegetation recovery and growth in good condition.Yulin vegetation, in general, give priority to improve whose total area of 39216.9588 km2, accounting for 90.7165% of the yulin.Degraded regions were less but still exist, which mainly distributed in basin of Kuye River, Wuding River and Lu River.4.Changing differences of NDVI in different land use types from 2000 to 2014 Yulin region to some extent reflects the growth conditions of different vegetation types. In general,the various land use types of vegetation has a good improvement,according to average annual growth rate,the rank of NDVI can be shown: Grassland>Cultivated land>Forest land>Sand>Bare land>Saline-alkali land.Significant sort of vegetation changes are as follows:Sand area>Forest land>Grassland>Bare land>saline-alkali land>Cultivated land.5.The correlation between NDVI and DEM(elevation and slope) is not obvious,and there is a certain correlation between the climatic factors(precipitation and evaporation)and NDVI.