A field and modeling study of subsurface stormflow for Huanggou Hillslope

Study region: The Huanggou Hillslope in China Study focus: The study of the threshold behavior and nonlinear characteristics of subsurface stormflow is not only essential for hydrology theory but also for flash flood disaster prevention. However, the formation mechanism and determination method of the thresholds have received little attention. Firstly, this study proposed the three-stage subsurface stormflow mechanism hypothesis. Secondly, based on in-situ observation, this study utilized the piecewise regression method and the soil moisture accounting method to analyze the threshold behavior and verify the three-stage mechanism hypothesis. And found that at the Huanggou Hillslope, the thresholds are related to the soil characteristic water content, and the sum of the thresholds of stratified runoff is approximately equal to the threshold of total runoff. Finally, this study developed the three-stage subsurface stormflow-based model (TSSM) and applied it to the Huanggou Hillslope and the New hydrological insights for the region: The results show that TSSM performed well, with NSEs of 0.82 and 0.67 in the calibration and verification periods of the Huanggou slope, and NSEs of 0.76 and 0.74 in the calibration and verification periods of the Huanggou Watershed, respectively. This study elucidated the three-stage subsurface stormflow mechanism and developed an effective simulation model, which contributes to increasing our understanding of three-stage subsurface stormflow and is beneficial for hydrologists to develop more realistic hydrological models.