Subsurface stormflow: Process advancements (1965–1974)

<jats:title>Abstract</jats:title> <jats:p>The International Hydrological Decade (1965–1974) was a crucial period that revolutionized the scientific understanding of subsurface stormflow, elevating it from a contentious hypothesis to a fundamental aspect of modern hillslope hydrology. Initially, doubts were raised, notably in Freeze’s 1974 review, about the significance of subsurface stormflow in storm runoff. However, empirical studies conducted during this era demonstrated that subsurface stormflow predominance is situational, becoming prominent mainly during substantial, rainy antecedent storms, with smaller events being influenced by surface overland flow saturation. Four pivotal process revelations reshaped the conceptual framework of stormflow formation: (1) subsurface boundaries generating perched saturation and lateral flow; (2) saturated wedges expanding uphill during storms; (3) topographic convergence zones, particularly hollows, acting as key sites for subsurface stormflow discharge; and (4) soil pipes and preferred flowpaths clarifying swift subsurface hydrograph responses. Together, these findings established a fluid, spatially diverse perspective on runoff creation—a perspective that continues to guide ongoing investigations into connectivity, thresholds and catchment-scale modeling of subsurface stormflow.</jats:p>