Soil thermal memory regulates event-scale precipitation recycling lag in a dryland environment

Abstract. Precipitation events in dryland environments generate sharp but uneven adjustments in surface and atmospheric conditions. While the atmosphere recovers rapidly from rainfall-induced cooling, the soil retains a substantial portion of the cooling anomaly, creating a land-surface memory. Using multi-year, multi-layer observations from five stations in Ningxia, China, and ERA5 reanalysis, this study investigates how this soil thermal memory timescale (τ_rec) modulates the timing of recycled moisture return.

Analysis of 112 events reveals a consistent "cold-humid pulse" with rapid atmospheric recovery but slow soil recovery, whose persistence we quantify as τ_rec (20–80 hours) using an exponential-decay framework. ERA5 diagnostics show the recycled moisture signal peaks 20–40 hours after rainfall, defining a recycling lag (τ_RR). Event-wise analysis of ten long-duration events reveals a systematic positive correlation (R ≈ 0.57) between τ_rec and τ_RR.

Longer soil memory consistently predicts a more delayed recycling peak. We show this relationship is mediated by enhanced moisture-heat feedback (H), where persistent cold soils slow boundary-layer recovery and postpone the reactivation of evaporation. These results identify soil thermal memory as an active regulator; the timing of recycled moisture is not solely an atmospheric process but is partially land-controlled. This work establishes a novel "coupling-memory-recycling" pathway, providing a new mechanism for understanding and modeling dryland precipitation dynamics.