Vegetation Coverage Change And Its Topographic Differentiation Characteristics In The Haihe River Basin

Based on the SPOT VGT/NDVI dataset from 1998 to 2013,DEM data,with the support of ArcGIS technology,by using geoscience information atlas,the spatial distribution and dynamic changes of vegetation coverage in Haihe River Basin during the past 16 years were analyzed.Then the characteristics of vegetation coverage spectrum in Haihe River Basin were studied.Furthermore,the differences of vegetation coverage mean value and the vegetation coverage spectrum in four topographic factors of elevation,slope,aspect and topographic relief were discussed respectively.Drawed the following main conclusions:(1)On the spatial distribution of vegetation coverage,the proportion of area was as follows:higher>middle>low,and the areas with poor vegetation coverage were mainly concentrated in the Bohai Bay area and around the city of Beijing and Tianjin and the western mountainous area.The dynamic change of vegetation coverage in the study area showed an overall upward trend during 1998-2013.Some improvements were made in the northwestern region in the Haihe River Basin.However,the central and eastern parts of Haihe River Basin and some urban central areas were degraded,and the vegetation coverage grade structure showed the trend of optimization.(2)On Topographic gradient difference of vegetation coverage,at different altitudes,vegetation coverage decreased first and then increased with the elevation of altitude.The low and high vegetation coverage were the most widely distributed on the low elevation of<200m,while the middle vegetation coverage was mainly at 1000-1500m altitude.At different slopes,the vegetation coverage gradually increased with the increase of the slope of the basin,and the vegetation coverage of each grade were mainly distributed in the gentle slope(2-6 degrees).At different aspect,the difference of vegetation coverage was small,and in the sunny slope vegetation growth status than good.At different topographic relief,the vegetation coverage decreased with the increase of topographic relief.The vegetation coverage of all grades was the largest on the low relief of 0-50m.(3)On spectrum characteristics of vegetation coverage change,in 1998-2001 spectrum units mainly were that vegetation coverage grade were bad,and its spatial distribution was relatively concentrated,which was the most prominent in the northwest of the basin.In 2001-2004,the total area of vegetation coverage was reduced,while the vegetation coverage was generally higher.In 2004-2013,the total area of vegetation cover change continued to decrease,and the vegetation coverage was developing in the direction of stability.The spectrum pattern of vegetation coverage change was mainly the stability type,which indicated that the vegetation coverage of Haihe River Basin was higher and more stable.The second was repeated conversion type and late conversion type,which was mainly distributed in the west of the basin,the southwest and the southern part of Tianjin.The vegetation coverage change spectrum pattern were the middle and high vegetation cover conversion.(4)On topographic gradient differences of vegetation coverage change spectrum,at different altitudes,the stability type tended to be V-shaped with the elevation of altitude,but the area of the change pattern was smaller and mainly concentrated at the altitude of 1000-2000m.At different slopes,the stability type increased with the increase of the slope.While the area of the change type pattern was smaller,and mainly concentrated on the flat slope and gentle slope(<6 degrees).At different aspect,the degree of vegetation coverage change from big to small was:shady slope,semi-overcast slope,semi-sunny slope,sunny slope.At different topographic relief,With the increase of terrain undulation,the stability type presented a trend of first decline and then rise,while the area of the change pattern was smaller,and mainly concentrated in the middle low relief area(50-200m).