Processed Global Groundwater Level (GWL) Observations in Europe

This dataset provides processed, quality-controlled, and gap-filled monthly groundwater level (GWL) observations across Europe, derived from in-situ measurements available through the Global Groundwater Monitoring Network (GGMN). The dataset was developed to support large-scale groundwater analysis, model evaluation, and satellite–model integration studies.
The original GWL observations were obtained from the GGMN portal and comprise heterogeneous station records with varying temporal coverage and data completeness. To ensure data reliability and representativeness at the continental scale, only monitoring stations with at least 40% temporal coverage over the study period were retained. Stations with shorter, highly fragmented, or insufficiently documented records were excluded.
To improve temporal continuity while preserving observed variability, missing values in the retained time series were reconstructed using a hybrid statistical gap-filling approach that combines Least Squares Principal Component Analysis (LS-PCA) and Iterative PCA (IPCA). This method exploits both spatial and temporal correlations among groundwater monitoring stations, enabling robust estimation of missing observations while minimizing reconstruction error and avoiding over-smoothing of groundwater dynamics.
The resulting dataset provides spatially distributed, temporally consistent monthly groundwater level time series suitable for validating large-scale groundwater storage products, assessing hydro-climatic variability, and supporting hydrological and data assimilation studies. Groundwater levels are reported relative to local station reference datums; therefore, the dataset is most appropriate for analyzing temporal variability, anomalies, and trends, rather than absolute hydraulic head comparisons across stations.