Antecedent state and the temporal organization of soil moisture response to episodic rainfall

Standard ecohydrological analyses typically frame soil moisture dynamics as direct responses to discrete rainfall episodes. However, this “forcing-first” perspective implicitly assumes that subsurface response timescales are synchronized with atmospheric intermittency—an assumption that breaks down when soil moisture dynamics bridge multiple storms or when storage depletion occurs within shorter timescales.  Here, we demonstrate that relying on meteorological event definitions leads to a fundamental mischaracterization of the temporal organization of soil storage. By applying an anomaly-based signal analysis to multi-year, profile-resolved field observations, we decoupled subsurface storage dynamics from rainfall timing to isolate observable patterns of soil response.  The analysis reveals two critical dynamics that event-based logic obscures. First, antecedent wetness is associated with a distinct regime-dependent transition in response structure: broadly distributed, multi-day storage anomalies in dry conditions contract into rapid, sub-day drainage pulses in wet conditions. This effectively decouples the subsurface response duration from the rainfall duration. Second, soil moisture dynamics frequently integrate multiple distinct precipitation episodes into single, coherent observed storage trajectories, particularly in deeper layers. These findings show that the temporal organization of soil moisture is governed by the interplay of forcing and antecedent state, not merely by rainfall timing. We conclude that forcing-based definitions are insufficient for capturing effective system memory, and that accurately characterizing ecohydrological function requires defining events by their subsurface response rather than their atmospheric input.