ENSO or the Atlantic: Which Actually Governs the Hydrological Vulnerability of the Caatinga?

ABSTRACT Global semi‐arid regions act as critical sentinels of the climate crisis, where water variability determines the resilience of ecosystems and societies. In the Caatinga biome, precipitation governance has been historically attributed to the El Niño–Southern Oscillation (ENSO) phenomenon; however, this study challenges this paradigm by demonstrating that the Atlantic Ocean exerts a statistically dominant influence on regional water vulnerability modulation. Using high‐resolution CHIRPS data processed via Google Earth Engine and a robust statistical approach with the Seasonal ARX/HAC model, we regionalised the biome into six distinct rainfall districts to isolate oceanic signals. The results reveal a climatic hierarchy where the Atlantic Interhemispheric Variability (PC2) controls drought thresholds more intensely than ENSO (PC1). Quantitatively, PC2 explained a precipitation deficit up to 77% higher than PC1 in the northern districts, acting as the primary driver for the Intertropical Convergence Zone (ITCZ) positioning.