| In this paper, it selected multi-source remote sensing image data before and after Wenchuan Earthquake on May12th,2008in Beichuan County. The landslides, collapses and mudslides were interpreted from Formosat-2image which took after Wenchuan Earthquake. And the interpreted result was validated with GPS receiver. The images before and after the earthquake was obtained to extract vegetation covering information using normalization difference vegetation index(NDVI),and used NDVI to estimate vegetation coverage. Then defining the vegetation damage degree index (VDDI) of the vegetation which was the difference of the normalized difference vegetation index before and after earthquake. The vegetation cover and damage were calculated, and studied the spatial distribution characteristics. Analysising the vegetation coverage level trends from2009to2013in Beichuan County, and using Markov model to predict the vegetation cover level position to2020. The results showed that:(1) Before the earthquake in Beichuan County high vegetation cover and medium to high vegetation covering the area occupied by two level accounted for95.84%of the total area of the study, dropped to87.67%after the earthquake, the earthquake in Beichuan County made vegetation damage significantly.The area of vegetation damage are mainly concentrated in Beichuan-Yingxiu fault zone surrounding area, and in mild improvement area of this level,969.88km2, accounting for the the study total area of33.86%. Slight damage and moderate damage after the earthquake in the main, the total area of vegetation destruction of850.34km2, accounting for29.68%of the total area of the study.(2) The three disasters region before the earthquake mainly to high and high vegetation cover, respectively, representing57.76%,80.24%and69.74%of the area of damage to vegetation, respectively, in low-level and low vegetation coverage area share minimum for13.04%,0.12%and0.15%. After the earthquake, medium and low and medium vegetation coverage area accounted for80.33%,95.29%and98.14%of the area of damage to vegetation, high vegetation coverage level of the area occupied by smaller, accounted for5.58%,0.03%and0.69%of the area of damage to vegetation.In the study area severe damage area of the total proportion of the disaster area, reached62.23%, three different types of disasters on the degree of destruction of vegetation in descending order of mudslides> collapse> landslide. The destruction of vegetation the regional distribution affected by the terrain, destruction of vegetation are closely related to elevation, slope, mainly at range of an altitude of800to2000m, and slope25°to45°, and weakly related to the aspect type.Destruction of vegetation area located by the water system the more obvious effects. The number of points of damage to vegetation increases tended to decrease with the distance between river from the water system, the largest number less than the destruction of vegetation point distribution within200m, accounting for29.82%of the total number of vegetation damage,70.86%destruction of vegetation point distribution from the river0-600m range.(3)The vegetation recovery after the Wenchuan earthquake in Beichuan County was good. There was a significant reduction in low-level vegetation coverage area every year from2009to2013, covering an area of transformation to high-grade vegetation, and the high-grade vegetationcoverage area had a significant increase year after year. Using Markov model to predict that in2020year, the area of high and medium to high vegetation will be increased to2828.70km, accounting for98.75%of the total area of the county. It means that the vegetation restoration measures being taken in Beichuan County is effected, and it need to countinue to hold in the future, so that the county environment has been further improved. |
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