Analysis of land cover conversion scenarios based on land-valleys-water coupling interface zones in Three Gorges Reservoir

The reservoir water level of the Three Gorges reservoir is gradually raised by means of phase water storage. The rise of water level is bound to direct the expansion of the water area, and then land cover will inevitably be overwhelmed and replaced, with the ultimate result of mountain, valley and water interface change. The research on temporal and spatial pattern of land cover conversion in the Three Gorges Reservoir Area attracts a lot of attention owing to reservoir water level fluctuation. In this study, land use/cover classification system was proposed in view of the continuity of the flooding time and differences in land cover natural features. The characteristics and trajectories of land cover conversion at the different operation phase of the Three Gorges Reservoir were analyzed based on Four-term multi-temporal land use/cover remote sensing data, the water system and DEM data. And thus, the distribution characteristics of main land cover conversion types on land, valleys and water coupling interface zones and in the condition of different terrain factors that need to be studied further also were summarized. The results showed that land cover in the Three Gorges Reservoir Area varied in degrees of conversion, while the overall spatial pattern remained more or less the same. It consisted mainly of seasonal green land cover and evergreen land cover, accounting for more than 96% of the whole reservoir. In addition, land cover conversion was considerably different in direction and scale throughout the operation phase of the Three Gorges Reservoir Area. More notable was that the main ways of land cover conversion at the three operation phases of the Three Gorges Reservoir were basically consistent, that were, the conversions between seasonal green land cover and evergreen land cover, the conversions of seasonal green land cover to gray land cover, and green land cover as well as blue land cover to water. However, the phased differences of spatial distribution and extension of major land cover conversion were remarkable. Furthermore, form the local point of view, there were also sharp phased differences in land cover conversion on land, valleys and water coupling interface zones. It was the conversion between land cover on land-land interface zones that was the main way at the first two phases(1997-2003 and 2003-2006), while land cover conversion on land and valleys interface zones was the most prominent from 2006 to 2009. Moreover, the conversion directions of the same land cover types on land, valleys and water coupling interface zones had changed at different operation phase. Finally, the distribution of land cover conversion was basically in accordance with natural and human activities laws. Altitudes and slope had significant impact on land cover conversion through Three Gorges Reservoir Area, but slope aspect only had an outstanding impact on land cover conversion at flooded area. Overall, these results indicated that the spatial characteristics of local land cover conversion at three operation phase of the Three Gorges Reservoir, and they were helpful for land use planning and ecological environment protection in the reservoir area.