Scale-dependent transition in soil moisture memory and its environmental controls in complex mountain terrain

Abstract

Soil moisture memory (SMM)-the persistence of soil moisture anomalies-is a key factor preconditioning hydrological responses and geohazard susceptibility. However, how SMM varies across timescales and the controls governing its persistence in complex terrain remain poorly understood. Here, we quantify SMM dynamics from daily to interannual scales using 20-year (2003–2022) daily soil moisture data from three contrasting watersheds in southwestern China, prone to soil erosion (Dali River Basin), shallow landslides (Anning River Basin), and debris flows (Jiangjia Ravine). Integrating Power Spectrum Analysis (persistence strength), Detrended Fluctuation Analysis (DFA-2; persistence duration), and scale-dependent attribution via Boruta random forest with partial correlation, we identify a pronounced scale-dependent transition in SMM and its drivers. SMM intensity generally weakens with increasing timescale, yet humid catchments exhibit surprisingly strong and persistent memory extending to multi-year scales. Feature importance analysis reveals a critical structural shift around the 5-year scale: short-term memory is dominated by atmospheric forcing and vegetation, whereas long-term persistence is controlled by soil properties and topography. This transition marks a conceptual shift from event-driven fast-response (topography-mediated) to storage-dominated slow-response (soil-buffered) regimes. These findings provide a framework for distinguishing short-term hydraulic preconditioning from long-term background susceptibility, proposing a conceptual framework for incorporating memory timescales into multi-scale geohazard assessment.