Revisiting the Dunne Diagram: Seasonal Variation and Spatial Pattern of Runoff Components

Abstract The classic Dunne Diagram qualitatively illustrates how atmospheric conditions, soil, and topography shape runoff generation mechanisms under long-term average conditions. This study revisits the diagram using a novel theoretical framework that unifies infiltration excess and saturation excess runoff into a continuous scheme governed by dynamic soil moisture variations across catchments. The framework captures the spatial and temporal transitions between runoff mechanisms. Using observational data from 600 natural catchments across diverse US atmospheric conditions and landscapes, we develop a data-driven, quantitative reinterpretation of the Dunne Diagram based on multiannual catchment behavior, and further examine runoff generation mechanisms at seasonal timescale. At the mean annual scale, saturation excess runoff dominates the West Coast and Eastern United States, infiltration excess runoff prevails in central regions, and baseflow dominates the Western interior and Appalachian areas. In the western United States, both saturation- and infiltration-excess runoff exhibit strong seasonality, closely following the precipitation patterns along the West Coast. Individual catchments show seasonal switching and coexistence of dominant runoff generation mechanisms. The Unified Scheme for Modeling Saturation and Infiltration Excess Runoff (URSSIE) model broadly reproduces the general pattern of the Dunne Diagram and provides quantitative support for the Dunne Diagram. This approach enhances the understanding of runoff processes and improves hydrologic modeling at catchment scales, with important implications for flood forecasting and water resource management in complex or changing hydrologic regimes.