Background The Loess Plateau, one of the most severe soil erosive areas in the world, is discharging large amounts of sediment to the Yellow River, resulting in serious sedimentation of the downstream channel. Assessing the relationships between rainfall, runoff, and sediment in the watershed may provide critical insights for understanding hydrological and soil erosion processes which are vital to sustainable management of watershed. This study attempts to analyze characteristics of runoff and sediment yield and their relationship with different rainfall patterns in the Yangjiagou watershed on the tableland-gully region of the Loess Plateau.

Methods This study applied the K-means clustering method and discriminant analysis method, and the rainfall events were classified using the runoff and sediment load data of the 184 rainfall events in the Yangjiagou watershed during 1981-2010. The power function was used to analyze the relationship of runoff and sediment.

Results Annual runoff and sediment load demonstrated significant decreasing trend (P < 0.01). Average annual value of the runoff and sediment load decreased by 50.32% and 55.64% in 1990-2010 compared to those during 1981-1989, respectively. The rainfall events were divided into three patterns. Pattern A was characterized by low rainfall amount (13.30-29.20 mm), medium duration (4.00-12.63 h) and medium rainfall intensity (1.80-5.00 mm/h). It included 149 rainfall events, accounting for 81% of the total rainfall events. Pattern B comprised of 32 rainfall events, accounting for 17%, which were characterized by high rainfall amount (48.73-75.05 mm), long duration (24.38-38.31 h) and low rainfall intensity (1.32-2.73 mm/h). Only 3 rainfall events belonged to pattern C, accounting for 2% of the total, and was characterized by medium rainfall amount (15.45-60.85 mm), short duration (0.57-4.40 h) and heavy rain intensity (27.65-38.60 mm/h). Pattern A was major rainfall pattern in the studied watershed, pattern B was similar to pattern A, and pattern C was extreme rainfall events. The proportions of the accumulated rainfall, runoff and sediment load among different rainfall patterns followed the order: pattern A>pattern B>pattern C. The runoff and sediment yield were mainly contributed by pattern A. The relationship of runoff and sediment transport modulus was well fitted by the power function with the best fit of pattern.

Conclusions The results reveal the basic characteristics of runoff and sediment yield for different rainfall patterns. Different rainfall patterns cause strong impact on runoff and sediment yield, and there was the strongest runoff and sediment yield capacity in pattern C, followed by pattern A and B. Decreased rainfall and increased vegetation cover result in the reduction of runoff and sediment yield in the studied watershed. The rainfall amount, duration and intensity significantly affect runoff and sediment yield.