Current theories of saturation-excess and infiltration-excess runoff fail to comprehensively and accurately elucidate the intricate runoff generation process in the Loess Plateau. It is imperative to examine the impact of preferred flow and plug flow on river runoff dynamics. This study elucidated the structural composition of runoff components by examining the literature on runoff formation mechanisms in the Loess Plateau. Subsequently, the runoff components of the Malian River Basin were accurately identified utilizing the Delayed-Flow Index (DFI). By integrating these mechanisms, the response components of preferred flow and plug flow were preliminarily delineated, their contributions across various regions were quantified, and their spatiotemporal heterogeneity was investigated. The findings indicate that during the generation of river runoff on the Loess Plateau, a complex interplay exists among precipitation, infiltration, groundwater flow, and surface runoff. River runoff is fundamentally the combination and accumulation of surface runoff, inter-soil flow, and groundwater runoff characterized by preferred flow and plug flow across varying temporal scales. The runoff in the Malian River Basin comprises four distinct components, ranked by contribution as follows: baseline-delayed flow (DB) > short-delayed flow (DS) > intermediate-delayed flow (DI) > long-delayed flow (DL). Furthermore, dual-axis response and ternary plot analyses confirm a significant “geomorphological control effect” on runoff patterns. As the landscape evolves from fragmented loess ridges and mounds (upstream) to intact tablelands (downstream), the runoff mechanism undergoes a fundamental shift from “fracture-led preferred flow” to “matrix-driven plug flow,” exhibiting a distinct linear migration trajectory in ternary space. During this transition, surface quick flow (34%–52%) remains relatively stable as a “basal support” for runoff composition, while the shift in subsurface flow regimes drives the non-stationary evolution of the runoff structure. This discovery quantitatively reveals the “hereditary” control of geomorphological evolutionary stages on groundwater recharge paths in the Loess Plateau, where increased topographic fragmentation facilitates preferred flow, while geomorphological integrity favors plug flow dominance.
Tong et al. (Wed,) studied this question.