Runoff and soil loss in a typical subtropical evergreen forest stricken by the Wenchuan earthquake: Their relationships with rainfall, slope inclination, and vegetation cover

Abstract

Earthquakes cause serious environmental problems for restoration and reconstruction of the area. Previous studies evaluated the consequences of soil loss and runoff from earthquakes. Some studies estimated soil loss and runoff amount precisely, but empirical studies on in situ and high geomorphic variability are lacking. This study was carried out in Xiaoyudong Township of Pengzhou County, China, in a typical subtropical, moist climate zone, with the vegetation of a subtropical, evergreen forest where the most destructive earthquake, named the Wenchuan earthquake occurred in May 12, 2008. This severe earthquake was followed by more than 30,000 aftershocks causing devastating landslides, soil erosion, runoff, and vegetation loss, which make the fault zone in the Longmen Mountains of Sichuan Province a perfect study area. The broad objective of this study was to estimate the sediment amount generated by the Wenchuan earthquake. The results show that (1) more runoff and soil loss occurred in landslides than at forested sites after the earthquake; (2) runoff and soil loss have positive linear correlations with rainfall amount and slope gradient, but there is a negative exponential correlation between vegetation cover and runoff, as well as soil loss; and (3) classification grades of soil erosion intensity reveals that total soil loss of very severe grade was 14.3% at the landslides sites. Moreover, 4.72 × 10⁶ t (4.65 × 10⁶ tn) of soil was still strikingly lost from landslides two years after the earthquake.