Monitoring vegetation recovery after China's May 2008 Wenchuan earthquake using Landsat TM time‐series data: a case study in Mao County

Abstract

The Wenchuan earthquake (Richter scale 8) on 12 May 2008 in southwestern China caused widespread ecosystem damage in the Longmenshan area. It is important to evaluate natural vegetation recovery processes and provide basic information on ecological aspects of the recovering environment after the earthquake. To circumvent the weather limits of remote sensing in the Wenchuan earthquake-hit areas, and to meet the need for regional observation analyses, three Landsat TM images pre-and post-earthquake in Mao County were used for analysis. Post-earthquake normalized difference vegetation index (NDVI) values were compared to pre-earthquake values with an NDVIbased index differencing method to determine the extent to which the vegetation was damaged in relation to the pre-earthquake pattern, and the rate of recovery was evaluated. The spatial characteristics of vegetation loss and natural recovery patterns were analyzed in relation to elevation, slope and aspect. The results indicated that severely damaged sites occurred mainly in river valleys, within a range of 1,500-2,500 m elevation and on slopes of 25-55°. The distance from rivers, rather than the distance from active faults, controls the damage patterns. After 1 year of natural regeneration, 36 % of the destroyed areas showed a decrease in NDVI value, 28.8 % showed very little change, 19.1 % showed an increase, and 16.1 % also increased with a recovery rate greater than 100 %. Moreover, there is a good correlation between recovery rate and both slope and elevation, but recovery patterns in the damaged area are complicated. Our results indicate that natural recovery in this arid valley is a slow process.

Ash fall impact on vegetation: a remote sensing approach of the Oldoinyo Lengai 2007–08 eruption

“…The NDVI trend analysis was carried out for three time spans: the pre-eruptive period ( Second, different recovery indices were calculated for the different time intervals following the eruption (Table 1). Previous studies proposed vegetation recovery indices based on spatial comparison between undisturbed and deteriorated vegetation within the same scene (e.g., Diaz-Delgado et al 1998;Diaz-Delgado et al 2003;Riaño et al 2002) or through temporal comparison of the vegetation state within each pixel separately (e.g., Gouveia et al 2010;Hope et al 2012;Lu et al 2012). The high vegetation variability within the study area makes it difficult to select unambiguous control sites for spatial comparison.…”

“…The 'Change in NDVI' parameter (T c ) is similar to the 'Lack of greenness' , with opposite sign, but it is normalized by the value of the pre-event NDVI (Lu et al 2012), whereas the 'Stand Regeneration Index' (SRI) is a simple ratio between the post-and pre-event NDVI. The 'Vegetation Recovery Rate' (VRR) is a ratio of the recovery after the eruption and the change in vegetation caused by the eruption: the NDVI value recorded for the month following the end of the eruption (NDVI erup ) is subtracted from the pre-and post-event NDVI values (Chou et al 2009;Lu et al 2012). Finally, we propose the Ash Recovery Index (ARI) which is an adaptation of the VRR index based on Hope et al (2012).…”

Monitoring Earthquake-Damaged Vegetation after the 2008 Wenchuan Earthquake in the Mountainous River Basins, Dujiangyan County

“…Liu et al monitored the early vegetation recovery within two months of the earthquake using MODIS GPP time-series products [12]. Lu et al (2012) used a time series of Landsat TM imagery to quantitatively assess the vegetation damage and monitor the vegetation recovery process after the earthquake and its associated secondary disasters [13]. Jiao et al assessed the spatiotemporal variations in vegetation recovery after the earthquake using the Normalized Difference Vegetation Index (NDVI) based on the Landsat images [14].…”

Monitoring Geologic Hazards and Vegetation Recovery in the Wenchuan Earthquake Region Using Aerial Photography

“…The vegetation recovery mainly occurred in elevations below 3,000 m, accounting for 99.27% and 99.15% of the total debris flow area in 2008 to 2009 and 2009 to 2011, respectively, and the peak occurred between the elevation of 1001-1500 m because of the abundant accumulational soil mass, which was suitable for vegetation growth, produced by the landslides and debris flows. The slope of the surface also have a obvious influence on the progress of vegetation recovery, and more than 60% of the vegetation recovery were concentrated on slopes between 31° and 50°, the peak occurred between the slope of 41-50°, Lin et al [55] and Lu et al [3] also observed similar results, they suggested that grass species that survived during this slope range facilitated the vegetation growth when adequate rainfall was supplied to the area. In addition, the good soil holding and storing water condition for the plants in the hazard sites is also critical to the vegetation recovery.…”

“…Subsequently, the vegetation recovery slowed due to woody plant re-establishment. The recovery patterns in the hazard areas were complex, with factors such as the terrain and soil also affecting the recovery's progress [3] and making vegetation recovery difficult (as with the No. 14 and No.…”