Dynamics Of Vegetation Cover And Desertification In Shiyang River Basin

Shiyang river is an inland river located in hexi corridor area of gansu province.Developing dynamic monitoring of desertification is of great importance to formulate reasonable protection policies and effective implementation of control measures in shiyang river basin.Based on the Landsat TM/OLI remote sensing image from 1995 to 2015,the desertification difference index was calculated based on normalized vegetation index and surface albedo.The image element binary model was used to calculate the FVC of each watershed.The vegetation difference index of different time periods in the watershed was calculated based on the normalized vegetation index of phase 3.The spatial distribution of different desertification degrees and the change of area transfer in the shiyang river basin were studied.The spatial distribution of different FVC and the change of area transfer in the whole watershed were studied.Whether vegetation degenerates or improves in different areas every 10 years during the monitoring period was studied,and the area of degraded or improved areas was statistically analyzed.The research results are as follows:From 1995 to 2015,the desertification area and distribution area of shiyang river basin were changing.There are also large areas of extreme desertification.In 1995,its distribution was mainly in the middle and lower reaches of the basin,the oasis desertification transition zone and the desert area.In 2005,its main distribution area decreased.In 2015,its distribution scope was significantly reduced,especially in the downstream areas of civil service.Severe desertification distribution range in 1995 are mainly distributed in the north and the west,until 2005,expanded its distribution range of the south,and in 2015 its distribution range gradually shrinking,mainly distributed in the north.In 1995,moderate desertification was mainly distributed in the oasis area and the low mountain area and the oasis desert transition zone,which decreased in 2005 and gradually spread to the south in 2015.Mild desertification was mainly concentrated in the southern mountainous areas and the northern oasis in 1995.In 2005,it increased to the northwest and the northern oasis in 2015.In general,the area of desertification in the shiyang river basin was 89.05 percent in 1995,85.77 percent in 2005 and 86.85 percent in 2015,indicating that the total area of desertification in the basin tended to decrease in 20 years.In the shiyang river basin,the distribution area and range of vegetation coverage are also changing in the past 20 years.In 1995,low and medium FVC were mainly distributed in the middle and north of the basin.By 2005,the range of medium and low vegetation coverage was reduced,and the main change was to low vegetation coverage.In 2015,the low vegetation coverage was largely reduced,mainly in the lower reaches,and mainly changed to the low and medium vegetation coverage.The medium vegetation coverage is mainly in the middle and northern oasis desert transition zone,and the distribution range has not changed much in 20 years.High vegetation coverage in 1995,mainly distributed in the southern mountainous area in northern and central oasis distribution have small amplitude decreases,and in 2005 and in 2015 continued to spread in north central,southern shrink.The high vegetation coverage was mainly distributed in the southern and northern oases in 1995.By 2005,the distribution had a trend of extending to the northwest,northeast and north,and the original distribution had a small decrease in 2015.In 20 years,the low vegetation coverage first increased and then decreased.The low and medium vegetation coverage first decreases and then increases.The FVC of medium and high vegetation first decreases and then increases.High vegetation coverage first increases and then decreases.The sheyang river basin experienced the most extensive vegetation improvement from 1995 to 2005.Among them,severe vegetation degradation areas were distributed in a small amount in the central and western regions and southeast regions of the study area in the first 10 years,and in the southern region in the later 10 years,they tended to spread to the north and northwest.Areas with moderate vegetation degradation were mainly distributed in the central,central,western and northern part of the basin in the first 10 years,while oasis distribution in the middle and north decreased in the later 10 years.The areas with slight vegetation degradation were mainly distributed in the northeast,central and western regions,south and northwestregions in the first 10 years,while the areas with significant vegetation degradation in the latter 10 years.The slight vegetation improvement areas were distributed in the central,southeast and northern areas of the basin in the first 10 years,and the oasis desert transition areas in the middle and north of the basin in the latter 10 years,with a significantly enlarged scope.The areas with moderate vegetation improvement were mainly distributed in the transition zone and the periphery of the northern oasis in the central oasis mountain area in the first 10 years,but decreased in the middle and southern regions in the later 10 years.Vegetation in extremely improve the regional distribution in the first 10 years in northern northern qilian mountain and oasis interior,and after 10 years in the south of the original distribution and southeastern mountainous area and the northern minqin oasis has decreased.From 1995 to 2005,the ratio of vegetation degeneration in the whole basin was48.44 %,and that of vegetation improvement was 50.56 %.From 2005 to 2015,the proportion of vegetation degraded was 48.73 %,and the proportion of vegetation improved was 51.28 %.