LAUSR

At subannual timescales, terrestrial water storage (TWS) plays a critical role in the partitioning of precipitation into runoff and evapotranspiration, and Amazonia stands out due to the great amplitude of the annual cycles. In this study, we analyse the monthly variation of the water balance and extreme hydrological events using GRACE data for a watershed situated in the “arc‐of‐deforestation” in the Eastern Brazilian Legal Amazon. The existence of a correlation and lag time response between the monthly sea surface temperatures in the Pacific and North Atlantic and the variables of the water balance were also investigated. The results showed a weak seasonal cycle of evapotranspiration, with higher water intercepted by the vegetation canopy in the rainy season and higher potential evapotranspiration supplied by TWS in the dry season. The lowest value of water storage was reached in December 2015 during the strongest El Niño event observed in the analysed period (2002–2016). This value impacted the streamflow for at least the entire rainy season. The correlation analysis showed that positive anomalies of the Niño 3.4 index from October to March caused a significant decrease in precipitation in the following March to May and in November, a significant increase in the reference evapotranspiration in April and May, and longer lasting effects on the streamflow and TWS. Although the underlying mechanisms contributing to the time delays remain incompletely understood, the results indicate that consideration of the ENSO influence on the water balance and of the TWS influence on streamflow would improve flood and drought forecasts with benefits for water management.