关键词: 改进归一化水指数, Landsat影像, 三峡工程, 转移矩阵

Abstract: The Anqing-Wuhu mainstem segment in the middle and lower reaches of the Yangtze River serves as a critical habitat for diverse species, where the ecological quality of floodplain wetlands directly governs the stability of the entire ecosystem. Utilizing 30-meter resolution Landsat satellite imagery from 1994 to 2022, we classified the floodplain wetlands in the Anqing-Wuhu mainstem segment in the middle and lower reaches of the Yangtze River using fractional vegetation coverage (FVC). Through dynamic degree analysis and transition matrices method, we quantified vegetation cover transitions across different FVC tiers and analyzed their spatiotemporal variations. The results showed that vegetation coverage of the floodplain was mainly at high and medium-high levels of FVC, with an average annual FVC value of 0.6188. The average annual FVC showed an “increase-decrease-increase” trend. During 1994-2004, high-FVC areas decreased by 25.7 km², while medium and medium-low FVC zones expanded at annual rates of 3.0%·a^-1 and 2.7%·a^-1, respectively. After the operation of the Three Gorges Reservoir (2004-2015), floodplain dynamics were dominated by the outflow of water, as well as the inflow of high and medium-high FVC, with both comprehensive FVC dynamic degree and single dynamic degree of low FVC reaching peak during this period. During 2015-2022, FVC exhibited gradual recovery, primarily through medium-high to high FVC transitions, accounting for 15% of total transferred areas. Key drivers of FVC change in the study area included anthropogenic reclamation, Three Gorges flow regulation, riparian shelterbelt construction of Yangtze River, and implementation of the Yangtze River conservation strategy.

Key words: modified normalized difference water index, Landsat image, Three Gorges Project, transition matrix