Abstract:Longitudinal ridge, as one of the main tillage management, causes severe soil erosion on hillslope scale and makes great contribution to the soil loss in typical black soil region of Northeast China. Rainfall pattern is one of the main factors influencing hillslope erosion. The simulated experimental study was conducted to investigate the effects of rainfall patterns on hillslope erosion with longitudinal ridge in the typical black soil region. According to the erosive rainfall standard and rainfall pattern characteristics of natural rainfalls in the typical black soil region, the experimental design included five patterns of simulated rainfalls with the same total rainfall amount of 87.5 mm, covering intensive-type (rainfall intensity distribution was 50-75-100-125 mm/h), reduced-type (rainfall intensity distribution was 125-100-75-50 mm/h), peak-type (rainfall intensity distribution was 50-75-100-125-100- 75- 50 mm/h), valley-type (rainfall intensity distribution was 100-75-50-75-100 mm/h) and uniform-type (rainfall intensity was 75 mm/h), and the slope gradient was 5° which was the critical slope gradient of changing longitudinal ridge to contour cultivation. The results showed that total runoff volume had little difference among five rainfall patterns, while obvious differences in soil loss were observed. Soil loss of the peak-type treatment was 1.20, 1.63, 1.78 and 1.80 times higher than those of the valley-type, reduced-type, uniform-type and intensive-type treatments, respectively. Occurring frequency of three rainfall patterns (peak-type, valley-type and reduced-type) occupied more than 70% of total natural rainfall events, which could be one of the key reasons caused severe hillslope soil erosion with longitudinal ridge in this region. The time sequences of rainfall intensity in each rainfall pattern had great effects on runoff, soil erosion and their contribution rates to total runoff and soil loss. Except for 125 mm/h rainfall intensity, rainfall intensities occurred at the initial stage of the rainfall pattern had more contributions to total soil loss, compared with the rainfall intensities appeared at the middle stage and the end stage.
