Image interpretation and statistical analysis of vegetation damage caused by the Wenchuan earthquake and related secondary disasters

Abstract

Damage to vegetation caused by secondary disasters of the Wenchuan earthquake in severely damaged counties was estimated through the visual comparison of SPOT images acquired before the earthquake and ADS40 aerial images acquired after the earthquake, and a series of spatial analyses. In this paper, we (1) interpret 2-meter resolution aerial images that cover areas severely affected by the earthquake, and obtain statistical information on vegetation damage for the counties of Beichuan, Wenchuan, Maoxian, Lixian, Pingwu, Qingchuan, Anxian and Jiangyou; (2) spatially analyze the relationships between vegetation damage and slope gradient and distance from active faults using ArcGIS software to obtain information on vegetation damage under different geologic and geomorphologic settings; and (3) estimate the area of vegetation damage for the whole region using the above results for the areas covered by imagery. The results indicate that (1) farmland and grassland were less damaged than forestland was since they are mostly located on less steep slopes; (2) Wenchuan was the worst damaged county; and (3) the proportion of damage to vegetation first decreased and then increased with increasing distance from the three main faults of the Longmenshan fault zone owing to the combined effects of the three faults and the effects of regional geology and landforms.