Study On The Change Of Vegetation And Snow Cover In Wenchuan County Based On RS And GIS

Study on the change of vegetation and snow cover in Wenchuan County by usingthe technologies of remote sensing and geographic information system is of great significance to the protection and construction of the ecological environment in Wenchuan County.First of all,the multi-periods remote sensing data(Landsat 5 TM,Landsat 7 ETM+,Landsat8 OLI),terrain data and administrative boundary data were collocted.Multi-periods remote sensing data were processed.All data were projected into the same projection under the same coordinate system.Secondly,Models for extracting vegetation and snow cover were formulated by spectral analysis.The multi-periods vegetation and snow cover data were obtained by using the models,and the multi-periods vegetation coverage was estimated.Thirdly,the temporal and spatial variation of vegetation cover between 2007 and 2008 was analyzed.The distribution of the disappeared vegetation region between 2007 and 2008 along terrain was also analyzed.The temporal and spatial change of vegetation cover between 2008 and 2014 was analyzed.The distribution of the appeared vegetation region between 2008 and 2014 along terrain was also analyzed.The vegetation coverage of the appeared vegetation region in 2014 was discovered.Finally,the intra annual changes of snow cover were respectively analyzed in 2009 and 2016.The interannual changes of snow cover on March(between2009 and 2016),September(1993,2007),November(2008,2016)were analyzed.The snow cover along with the terrain was also analyzed.The study shows that: The region with vegetation in 2007 and without vegetation in 2008(i.e.,the disappeared vegetation region)accounted for 4.95% of the County area,which was mainly caused by the large earthquake on May 12,2008 and its secondary disasters.The region without vegetation in 2008 and with vegetation in 2014(i.e.the appeared vegetation region)accounted for 3.60%,which was mainly caused by artificial and natural vegetation restoration.The vegetation coverage of the disappeared vegetation region in 2007 was mainly the high coverage,which accounted for 85.88% of the disappeared vegetation region.The vegetation coverage of the appeared vegetation region in 2014 was mainly the high coverage,which accounted for 46.80% of the appeared vegetation region.area.The disappeared vegetation region mainly distributed in the elevation zone between 1000 m and 3500 m,and distributed in semi shady aspect more than other aspect types.The appeared vegetation region mainly distributed in the elevation zone between 1000 m and 3500 m,and distributed in semi shady aspect more than other aspect types.The study also shows that: the snow cover area in 2009 and in August was less than that in March.In 2016,the largest snow cover area in March,followed by November,and the smallest in July.The area of snow cover in March,2009 was less than that in March,2016.The area of snow cover in September,1993 was less than that in September,2007.The area of snow cover in November,2008 was more than that in November,2016.The snow cover in 2016 mainly distributed above 5000 m,and snow cover area in shady aspect was more than that in other aspect types.The results are important to the restoration and protection of vegetation and the scientific utilization of snow resources in Wenchuan County,and provide the relevant scientific and technological support for the construction of ecological civilization in Wenchuan County.