Combined effects of rainfall types and antecedent soil moisture on runoff generation at a hillslope of red soil region

Abstract

The runoff threshold is one of the important parameters in hillslope hydrology. Information on the combined roles of rainfall types and antecedent soil moisture in the runoff generation threshold is still scarce. Therefore, we linked the runoff generation behaviours of a 150‐m hillslope with rainfall types and antecedent soil moisture conditions during a 4‐year observation period between January 2017 and December 2020 in the red soil region of China. We found that the surface runoff of a hillslope could be modelled with a relatively high accuracy using HYDRUS 1D. Rainfall event types, classified into four types (I, II, III and IV) using a machine learning based k‐means clustering algorithm, significantly affected the modelling accuracy of runoff. The prediction accuracy decreased as the level of rainfall type increased, with R2 decreasing from 0.93 for type I to 0.41 for type IV and RMSE increasing from 0.0082 to 0.025 italiccm3italiccm−3 accordingly. The scope of the runoff threshold, represented by antecedent soil water storage of 0–30 cm and event rainfall amount (ASW+P), ranged between 97 and 139 mm. That is, when ASW+P was lower than the lower limit, no runoff occurred in all of the rainfall events, and runoff would be generated without considering the hydrological conditions if ASW+P was higher than 139 mm. The driving factors of runoff generation were strongly dependent on the classified rainfall types. Hourly maximum rainfall intensity was the main contributor to runoff generation for the relatively slight rainfall events (i.e., types I and II). The rainfall amount, however, played a dominant role for the rainfall types with larger amounts and intensities (i.e., types III and IV). These findings provide insights into the method of determining runoff thresholds as well as the inner mechanisms of runoff generation behaviours at the hillslope scale under regions with similar climatic and hydrological conditions to the present study. Highlights Heavy rainfall events were the main error sources of runoff modelling. The threshold of runoff generation was identified by the combination of antecedent soil moisture and rainfall. Threshold scope of runoff generation ranged between 97 and 139 mm. Rainfall classification is valuable in understanding runoff generation behaviours. Runoff driving factors depended on rainfall types.

The Lag Effect of Riverine Flow-Discharge and Sediment-Load Response to Antecedent Rainfall with Different Cumulative Durations in Red Hilly Area in China

“…Rainfall intensity severely affects flow-discharge lag time, and high-intensity and long-duration rainfall shortens the response time of river runoff [51]. Ordinary rainfall, on the other hand, requires the soil to reach the moist threshold for runoff to occur [14]. Rainfall and rainfall intensity are also important factors in the lag time of riverine flow discharge [52,53].…”

“…Antecedent rainfall increases soil moisture and reduces soil infiltration, so the significance of antecedent rainfall in sediment-load processes cannot be understated. Studies have confirmed that the runoff coefficient can double when the soil is moistened by antecedent rainfall, due to the acceleration of runoff generation with moist soils [14,15]. Antecedent rainfall increases soil moisture, improves runoff conversion efficiency, accelerates riverine runoff discharge [13,16], enhances water erosion, and increases riverine sediment loads.…”

“…Antecedent soil moisture correlates more strongly with riverine flow. Antecedent soil moisture and rainfall are the important factors influencing riverine flow discharge [14,19], and the combination of antecedent rainfall and intra-event rainfall is vital to generate riverine flow discharge and sediment loads [14,20]. Larger floods caused by extreme rainfall respond more strongly to antecedent rainfall [21,22].…”

Soil physics matters for the land–water–food–climate nexus and sustainability

“…They found that the crusted soil pores had a feature of a large number of nearly circular small pores, with the pore number and circularity decreased, while the equivalent diameter increased with the slope, mainly due to differences in the run‐off and sediment process, and crust formation process on slopes with different gradients. Based on a 4‐year field experimental study, Wang, Gao, et al (2022) demonstrated that rainfall strength and antecedent soil moisture conspire to determine the threshold of runoff generation, a key for runoff characterization. Hourly maximum rainfall intensity was the main contributor to runoff generation for the relatively slight rainfall events, while the rainfall amount determined the rainfall type with larger amounts and intensities.…”

Impact of Diverse Rainfall Patterns and Their Interaction on Soil and Water Loss in a Small Watershed within a Typical Low Hilly Region

“…Fubiao [23] studied erosive rainfall and sediment yield traits in the Puxiang River Basin in western Yunnan Province, unveiling distinct impacts of rainfall factors on runoff depth and sediment yield across varied land use types. Wanghe [24] investigated sediment production regularities on exposed slopes in red soil regions under diverse rainfall types, revealing a linearly positive correlation between runoff depth, soil erosion, and rainfall metrics such as precipitation (P), maximum 30 min rainfall intensity (I 30 ), and rainfall kinetic energy (E). Zhao Y [25] conducted various lab experiments examining rainfall effects on runoff and soil erosion, noting significant differences in the hydrograph, sediment graph, soil water content, and infiltration depth.…”