Strong ENSO Forcing of Wet Season Rainfall Extremes in the Eastern Amazon

Abstract

Recent years have seen strong droughts and floods in the Amazon basin, the largest center of atmospheric convection on land. To assess to what degree these events are extreme in a historical perspective requires accurate and long-term climate data, which are generally lacking for this part of the world. Here, we developed a 131-year oxygen isotope chronology from exactly dated tree rings of Cedrela odorata from the eastern Amazon Basin. The chronology (1885–2016) correlates strongly with observed wet-season rainfall totals (r = −0.71, 1951–2016) and stream discharge over the eastern equatorial Amazon. In contrast to oxygen isotope chronologies further inland that record basin-wide rainfall, our new record provides a good rainfall proxy for the eastern Amazon basin alone and shows that extreme precipitation events are also driven by ENSO.

Plain Language Summary

The Amazon Basin is a crucial ecosystem for global biodiversity and climate, yet recent extreme droughts and floods raise concerns about the hydrological cycle over the Basin. Understanding these climate extremes is limited by the lack of long instrumental observations before 1950. Tree-ring data can provide a valuable proxy for historical climate variability. Oxygen isotope measurements from tree rings of Cedrela odorata were used here to reconstruct wet season rainfall over the eastern Amazon from 1885 to 2016. The reconstruction is very highly correlated with regional rainfall and river discharge, and with indices of the El Niño/Southern Oscillation. The lowest rainfall total observed in the instrumental measurements and in the reconstruction occurred in 1983, during one of the strongest El Niño events in recorded history. The new reconstruction provides a valuable addition to the hydroclimatic record for the late 19th and early 20th century in a data sparse region of the eastern Amazon.