Historical Groundwater Memory Predicts Site‐Specific Persistence Horizons Across Germany

Abstract Groundwater levels retain memory of antecedent hydrologic conditions, but whether this memory defines a persistent timescale of later groundwater behavior remains unclear. We analyzed weekly records from 3207 wells across Germany, estimating groundwater memory during 1991–2005 and persistence during 2013–2022. Historical autocorrelation‐implied timescales strongly predicted later persistence horizons (Spearman = 0.851; 95% confidence interval, 0.819–0.877), with a median absolute difference of 2 weeks. A well's own historical memory was much more closely related to later persistence than memory reassigned among hydrogeologically and spatially similar wells, indicating strong site specificity. Historical hydroclimatic–groundwater coupling was also associated with departures from the autocorrelation‐based expectation, and this relation persisted after removal of seasonal and trend components. These site‐specific timescales inform persistence‐based forecasting and provide a temporal perspective for groundwater resilience assessment and climate adaptation planning.