Nonlinear Responses Between Watershed Hydrological Functional Connectivity and Rainfall‐Runoff‐Sediment

Abstract Hydrological connectivity plays a critical role in influencing the runoff‐sediment process within watershed, while its behavior under varying rainfall conditions remains unclear. In this study, total 221 rainfall events were classified into three types: I (long‐duration light rainfall), II (short‐duration storm rainfall), and III (long‐duration heavy rainfall). The end‐member mixing analysis was employed to assess the characteristics of runoff sources the hydrological functional connectivity index (IHC) of rainfall event was calculated. The results indicated that, type III generated significantly greater runoff and sediment yields compared to II and I. Regarding the composition of runoff sources, pre‐event water was the dominant contributor for types I and II, accounting for 73.09% and 71.84%, respectively. Conversely, event water constituted the primary source for III, contributing 54.33%. The IHC for type III was 1.19, which was notably higher than that of II and I. There were significant nonlinear relationship and threshold (IHC mean = 0.53) between IHC and the runoff‐sediment, which could be used to identify key areas for soil and water conservation and to implement timely management measures. When the IHC mean was below 0.53, events were mainly type I and II, governed by a low‐connectivity pattern dominated by subsurface flow, exhibiting limited sediment transport capacity. Conversely, events were mainly type III, governed by a high‐connectivity pattern driven by the coupling of surface and subsurface flows, resulting in stronger sediment transport potential. These results offer novel insights into watershed soil loss managing strategies through the lens of hydrological connectivity.