Effects of Rainstorm Patterns on Runoff and Sediment Yield Processes

Varying rainfall intensity during rainfall events is a common phenomenon, but little information is available concerning its effects on soil erosion processes. Five simulated rainstorm patterns (even, rising, falling, rising-falling, and falling-rising patterns), each with a different rainfall intensity pattern but with the same average rainfall intensity and total rainfall amount, were designed to quantify how rainstorm patterns affect runoff and sediment yield processes. The five rainstorm patterns were subjected to two slope gradients (5 degrees and 10 degrees) and two surface treatments that entailed the presence or absence of raindrop impact, in which the absence was simulated by placing nylon nets over soil pans. Results showed not only the total runoff but also each stage of runoff rate for a given rainfall intensity exhibited no significant differences among rainstorm patterns. However, soil loss from varying-intensity rainstorms was 1.13 to 5.17 times greater than that from even-intensity rainstorm, and the rising pattern was associated with the greatest soil loss. Moreover, each stage of soil loss by unit runoff for a given rainfall intensity was significantly different among rainstorm patterns. The variation in sediment regime and runoff hydraulic characteristic explained those. For sediment regime, in the presence of raindrop impact, for the rising pattern, soil detachment capacity was the dominant factor controlling soil loss, and for the other four patterns, runoff transport capacity was an important control on soil transfer, but it played different roles in soil loss under different patterns; in the absence of raindrop impact, the differences in sediment regime mainly reflected in transport capacity among storm patterns. With respect to flow hydraulic characteristics, the key hydraulic parameter (the parameter that had the greatest influence on soil loss) from varying-intensity rainstorms increased on average by 4.70% to 70.53% relative to those from even-intensity rainstorms.