Multiscale Evolution and Climatic Influences on Groundwater Drought in the Huaihe River Basin

Groundwater drought is characterized by delayed responses, long duration, and slow recovery, and its evolution is influenced by both local hydroclimatic processes and large-scale ocean–atmosphere variability. To investigate the spatiotemporal evolution and multiscale responses of groundwater drought, a Groundwater Drought Index (GDI) was constructed for the Huaihe River Basin (HRB) using Gravity Recovery and Climate Experiment (GRACE)/GRACE Follow-On (GRACE-FO) and Global Land Data Assimilation System (GLDAS) data from 2003 to 2025. The Bayesian Estimator of Abrupt change, Seasonality, and Trend (BEAST), Modified Mann–Kendall (MMK)–Hurst analysis, wavelet coherence, and Extreme Gradient Boosting–Shapley Additive Explanations (XGBoost-SHAP) were integrated to characterize trend shifts, persistence, multiscale hydroclimatic relationships, and teleconnection-related contributions. The results showed clear temporal variability and spatial heterogeneity in the GDI, with a basin-wide groundwater drought occurring around 2020. The basin-averaged GDI reached a minimum of −2.23 in June 2020, while the lowest sub-basin value was −3.25. The change points in the Shandong Peninsula and Coastal River systems (SPCR) and Yishu-Si River system (YSR) occurred in April 2018 and August 2019, respectively. The MMK–Hurst results indicated predominantly downward GDI trends across the basin, with persistent drying characteristics in parts of the central and northern HRB. Wavelet analysis revealed clear multiscale relationships between GDI and local hydroclimatic variables. Soil moisture (SM) had the largest proportion of significant coherence area (POSP = 19.47%). Shapley Additive Explanations (SHAP) analysis further identified the Interdecadal Pacific Oscillation (IPO) and Tropical South Atlantic Index (TSA) as the two most important teleconnection predictors, with Mean |SHAP| values of 0.1621 and 0.1314. The proposed framework provides a useful basis for groundwater drought monitoring, risk assessment, and basin-scale water-resource management.