ESTIMATING THE CHANGE OF VEGETATION COVERAGE OF THE UPSTREAM OF MINJIANG RIVER BY USING REMOTE-SENSING IMAGES

The upstream of Minjiang River, which was one of the main water sources for Chengdu Plain and the Yangtze River, was selected as the study area in the paper. With a series of cloud-free Landsat TM/OLI images acquired on June 24, 1994 and June 1, 2014, the vegetation coverage of the study area was calculated based on the vegetation index and dimidiate pixel model. The temporal and spatial changes of vegetation coverage were analyzed with digital elevation model and county area. The average vegetation coverage of the study area was decreased from 68.97% in 1994 to 60.39% in 2014. The analysis results showed that vegetation changes were closely related to topographical characteristics. The proportion of vegetation degradation area increased with the elevation increase and vegetation degradation was the most serious at the elevation range from 3500 m to 4500 m. The vegetation degeneration was the most obvious in Wenchuan County and Songpan County. Geological hazards caused by the earthquake and human disturbance were the main cause of the vegetation degradation and the aridity trend in the study area was another important factor.