We used wavelet coherence analysis to investigate the effects of precipitation (P) and groundwater dynamics (total water storage anomaly, TWSA) on evapotranspiration (ET) at kilometer, sub-basin, and whole basin scales in the Amazon basin. The Amazon-scale averaged ET, P, and TWSA have about the same annual periodicity. The phase lag between ET and P (Φ_ET-P) is ~1 to ~3 months, and between ET and TWSA (Φ_ET-TWSA) is ~3 to ~7 months. The phase patterns have a south-north divide due to significant variation in climatic conditions. The correlation between Φ_ET-P and Φ_ET-TWSAis affected by the aridity index (the ratio between potential ET (PET) and P, PET / P), of each sub-basin, as determined using the Budyko framework at the sub-basin level. The spatial structure of Φ_ET-P is negatively correlated with the spatial structure of annual ET. At Amazon-scale during a drought year (e.g., 2010), both phases decreased, while in the subsequent years, Φ_ET-TWSA increased, indicating strong groundwater effects on ETimmediately following dry years Amazon-wide.