Temporal and Spatial Evolution of Vegetation Coverage in the Mianyuan River Basin Influenced by Strong Earthquake Disturbance

The 2008 Wenchuan earthquake caused significant economic losses and degradation of regional ecosystems, including the terrestrial vegetation. Since the vegetation root system can enhance the soil’s anti-erosion capacity and therefore mitigate the occurrence of slope instabilities, it is beneficial to study the spatial and temporal evolution of vegetation for a long-term assessment of co-seismic secondary disasters. The Mianyuan River Basin, an uninhabited area passing through an active fault located in the earthquake-affected region, was selected as the study area. The Normal Difference Vegetation Index (NDVI) was calculated using remote sensing images from 1994 to 2017 to analyze the process of vegetation growth, loss, fluctuation and recovery. Statistical results suggest that the area in the middle and lower reaches, near the river network, and with a slope of 30 to 40 degrees were variable regions, showing more significant vegetation destruction during the earthquake and faster repair after the seismic event. Besides, vegetation near the fault was damaged more severely after the earthquake, but the active fault did not play an essential role in the vegetation recovery period. In the Mianyuan River Basin, vegetation experienced a volatility period (5 plus or minus one year) before entering the recovery period. In 8 to 9 years after the earthquake, the surficial vegetation could recover to the state before the earthquake.