Groundwater resources in arid regions like Saudi Arabia face severe threats from over-extraction and climate variability, impacting sustainability and food security. This study quantifies groundwater drought, evaluates spatiotemporal trends, assesses sustainability, and investigates global climate oscillations' influences on groundwater dynamics. GRACE/GRACE-FO-derived Terrestrial Water Storage Anomalies (TWSA), integrated with soil moisture, surface water, and precipitation data, computed Groundwater Storage Anomalies (GWSA). A standardized Groundwater Drought Index (GDI) assessed drought severity. Mann-Kendall tests, Sen's slope analysis, and Reliability, Resiliency, and Vulnerability indicators evaluated trends and sustainability. Spatial Self-Organizing Maps classified hydrological and climatological patterns. Granger-integrated VAR models and wavelet coherence assessed influences of global climate oscillations. Significant depletion occurred (2002-2023), notably in southern/eastern regions (-5.5 cm in 2023). Extreme drought affected over 1.95 million km(2) (2020). Low reliability (0.46), resiliency (0.03), and high vulnerability occurred in Najran and Asir, with strong GDI-ENSO/PDO coherence (2005-2015), emphasizing targeted groundwater management strategies.