Analysis Of Vegetation Coverage And Its Dynamic Change In The Three Gorges Reservoir Area In Chongqing Based On Remote Sensing

Vegetation is generally considered as the plant communities covered on the surface of the earth. It is an importand part and the foundation of the terrestrial ecosystems, as well as the natural link between soil, atomesphere and water. Vegetation and its change provide important information for hydrology, ecosystems and global changes. Vegetation coverage is a critical indicator for measuring the status of the vegetation, it is also an import parameter for plant communities and ecosystems, and plays an important part in revealing the rules of spatial change and evaluating the eco-environment.The Three Gorges project is a magnificent plan that has drawn the attention of the world, its construction will greatly affect on the economy, ecosystems and environment in the Three Gorges reservoir area. Therefore, getting information on the vegetation and its changes timely and rapidly plays an important role in studying on the land use and land cover change, properly usage of the natural resources and the sustainable development in the Three Gorges reservoir.Remote sensing images (MODIS-NDVI) from 2001 to 2008 were collected and analyzed to investigate the vegetation coverage and its dynamics changes in the Three Gorges reservoir in Chongqing. The parameters were determined by analyzing the physical meanings of dimidiate pixel model and were used to estimate the vegetation coverage of the study site. Then, the dynamics change and controlling factors of the vegation coverage were explored in the current study. The main results obstatined in this work were summaried as follow:(1) Establishment and calculation of the model. The Dimidiate pixel model was elaborately deduced and analyzed, and the impact factors of the parameter NDVIveg and NDVIsoil were discussed to effectively estimate the vegetation coverage. Then the newly mothod improved by the vegetation type and soil type data set was used to calculate the vegetation coverage from 2001 to 2008 in the study area.(2) Yearly changes of the vegetation coverage. There was an obvious rising trend of vegetation coverage from 2001 to 2008. The vegetation coverage in summer showed a generally rising trend in fluctuation with an overall increasing value by 2.44%. The vegetation coverage in spring and autumn showed similar trends with the yearly ratio of 0.37% and 0.38%, respectively. The vegetation coverage in winter showed a similar trend with that in summer but with a higher range.(3) Seasonal changes of the vegetation coverage. Significant seasonal changes of the vegetation coverage were presented in the study area due to the closely relationship between the vegetation coverage and climate and between the vegetation coverage and the phase of the vegetation growth. The vegetation coverage in summer was highest with an average value of 82.99%, and that in the winter was lowest with an average value of 61.53% due to the temperatural restriction to the vegetation growth. The vegetation coverage in spring and autumn were 76% and 74.52%, respectively.(4) Spatial distribution of the vegetation coverage. Significant spatial differences were found in the study area. The vegetation coverage of water body and river was 0. Due to the lack of vegetation, the vegetation coverage of the construction land, especially the urban areas. Lower values of vegetation coverage were also found in Yangtze river and its subrivers of Daning river, Pengxi river, Gundu river, Wujiang river and Chongqing urban areas. On the contray, higher values of vegetation coverage existed in Wuxi, northern part of Kaixian, Fengjie, southern part of Wushan, Shizhu, Fengdu and Wulong counties where there are large area of forest. Meanwhle, the vegetation coverage changed faster in these areas. Significant changes were also found in Jiangjin, Changshou, Zhongxian, Banan where there are large area of cultivated land.(5) Effects of topographic factors.①Elevation. The vegetation coverage increased with the elevation, but rising to the maximum at a critical altitude, then decreased with the elevation increasing. The critical altitude was the lowest in winter about 1100m, but the highest 2700m in summer,1800m and 1700m in spring and autumn, respectively.②Slope. The vegetation coverage obviously increased when slope<15°in the seasons. Vegetation coverage of spring, summer and autumn were slightly increased to the maximum and then slighted decreased to a steady when 1524°.③Aspect. The seasonal difference of vegetation coverage was significant in the same aspect. However, similar regular change and no significant difference existed in vegetation coverage of one season in different aspect. The vegetation coverage increased to the maximum with the aspect increasing from 0 to about 42°, then it reduced to the minimum when aspect was about 177°in winter while about 183°in other seasons.(6) Effects of land use types. Wood land had the highest vegetation coverage in all the land use tyeps,77.79% in spring,86.02% in summer,77.66% in autumn and 62.98% in winter. However, construction land had the lowest vegetation coverage,37.93% in spring,39.92% in summer,36.77% in autumn and 33.11% in winter. Cultivated land had the same vegetation coverage as grass land. The vegetation coverage of all land use types showed upward trend, especially in summer and construction land. Significant seasonal difference existed in different land use types. Mean vegetation coverage in summer was the highest but lowest in winter. The variation of vegetation coverage appeared the period from autumn to winter, and variation were over 10% of all land use except construction land due to human activity.