<p>Understanding the causal relationships between large-scale climate oscillations and regional meteorological drought is essential for improving drought prediction. This study applies the Synergistic-Unique-Redundant Decomposition framework to disentangle the causal contributions of four climate indices (Arctic Oscillation, Pacific Decadal Oscillation (PDO), El Niño-Southern Oscillation (ENSO), and Atlantic Multidecadal Oscillation) to meteorological drought variability in the Yangtze River Basin during 1961–2024. Drought variability is characterized using the Standardized Precipitation Evapotranspiration Index and rotated empirical orthogonal function analysis, yielding ten spatially coherent drought modes. Three principal findings are identified. First, unique causal contributions exhibit pronounced spatial heterogeneity, with different climate indices acting as the dominant independent drivers for distinct sub-regions. Second, synergistic interactions among climate indices substantially exceed the sum of individual contributions for several modes; in particular, the ENSO-PDO synergy accounts for 80% of explained causality in the Wujiang-Dongting region. Third, causality leakage reveals clear spatial differentiation. Five modes, distributed from the Yangtze Delta to upstream tributaries, exhibit leakage below 5%, indicating that the four climate indices explain over 95% of drought variability. In contrast, three upper basin modes exhibit leakage exceeding 90%, implying the dominance of local or unobserved factors. Seasonal analysis further reveals divergent temporal behaviors of synergistic effects, with some interactions being seasonally locked while others are strongest in annual analyses. These findings deepen our understanding of how multiple climate indices jointly influence regional drought and provide a quantitative basis for region-specific drought prediction.</p>