Abstract: Surface roughness is an important factor affecting sediment yield. Previous studies are focused on the effect of roughness on runoff and sediment characteristics rather than the relationship between microtopography changes and soil erosion and sediment yield process under different roughness conditions. In this study, the effects of rainfall intensity and land surface roughness on microtopography and runoff and sediment yield are studied by artificial rainfall experiments and Photoscan technique. Results reveal that in the experiment condition, four microtopographic factors, inclusive of surface roughness, relief amplitude, surface incision, and depression storage) decrease on both smooth and rough slopes after rainfall, and the decreasing trend aggravates with the further increasing of rainfall intensity. Under the same rainfall intensity and rainfall duration, microtopographic factors of rough slope change more dramatically than those of smooth slope.There is a significant positive correlation between the variation of topographic factors and the runoff and sediment yield parameters (runoff rate, sediment rate, accumulative runoff volume, and accumulative sediment yield), but the correlation is only based on the condition of the same initial slope treatment; under different slope treatments, the variation of microtopographic factors on the slope does not correspond with the amount of soil erosion.Compared with the smooth surface, the rough surface could effectively reduce runoff yield in the early stage of rainfall, and the yield on both slopes tends to be consistent with the elongation of rainfall duration.Under four rain intensities in the experiment, the runoff rates of rough slope and smooth slope both increase at first and then tend to be stable; the sediment yield and runoff rate of rough slope display the same trend; but on smooth slope, sediment yield increases rapidly at the early stage of runoff yield, and then decreases and finally tends to be stable. The research results provide reference for studying soil erosion mechanism and establishing hillslope erosion and sediment yield model.

Key words: rainfall intensity, roughness, microtopography factors, runoff yield, sediment yield