Influence of intra-event rainfall variation on surface–subsurface flow generation and soil loss under different surface covers by long-term field observations

Abstract

Abstract. Rainfall is the main driver of runoff generation and soil erosion. The impacts of natural rainfall on water erosion have been extensively studied at an inter-event scale; however, very few studies have explored the intra-event influences and associated responses to different surface cover types. In this study, long-term in situ field observations of surface runoff, subsurface flow, and soil loss characteristics in three surface cover plots (bare land, litter and grass cover) under natural rainfall events were conducted from 2002 to 2012 in the red soil hilly region of southern China. According to the period of most concentrated rainfall, 262 rainfall events were classified into four types of intra-event variation: advanced, intermediate, delayed, and uniform patterns. For bare land, the advanced pattern with the shortest duration and the highest intensity was main rainfall type for surface runoff and soil loss; the contribution rates were 57.24 % and 75.17 % for surface runoff and soil loss, respectively. Sediment yields were more sensitive to intra-event rainfall variation than surface runoff. The highest subsurface flow was found in the delayed pattern with the longest duration and high depth, followed by the uniform, intermediate, and advanced patterns. For all rainfall patterns, compared to the bare land, surface cover significantly reduced surface runoff and soil erosion by 88.01 to 91.69 % and by 97.80 to 97.95 %, respectively, while subsurface flow was increased from 3.55 to 5.92 times. The reduction benefits of litter cover were comparable to those of grass cover. However, the increasing benefit of subsurface flow for litter cover for each rainfall pattern ranged from 1.38 to 2.67 times those of grass cover. Moreover, surface cover weakened the influences of intra-event rainfall variation on surface-subsurface flow and soil loss. The results demonstrated that intra-event rainfall variation had important effects on surface-subsurface flow and soil loss, and provided a basis for optimizing surface cover measures to effectively respond to extreme water erosion and drought caused by global climate change.