Multidecadal Changes in Wet Season Precipitation Totals Over the Eastern Amazon.

Instrumental observations indicate that Amazon precipitation and streamflow extremes have increased during the last 40 years, possibly due to anthropogenic changes and natural variability. How unprecedented these changes might be is difficult to determine because some paleoclimatic, instrumental, and climate model simulations suggest that Amazonian precipitation and streamflow may be subject to multidecadal variability with return intervals longer than most direct observations. A new 258‐year long tree‐ring chronology of Cedrela odorata has been developed in the eastern Amazon and has been used to reconstruct wet season precipitation totals from 1759–2016. Reconstructed drought extremes are associated with significant sea surface temperature anomalies over the tropical Pacific and Atlantic Oceans. Strong multidecadal variance is identified in the reconstruction that may reflect a component of natural rainfall variability relevant to forest ecosystem dynamics and suggesting that recent hydroclimate changes over the eastern Amazon may not be unprecedented over the past 258 years. Plain Language Summary: Drought and flood extremes in the Amazon River basin have increased in frequency during the last 40 years, but how unprecedented these recent changes might be is difficult to determine because most instrumental records do not extend before 1950. A new tree‐ring chronology of Cedrela odorata has been developed in the eastern equatorial Amazon, confirming the exact dating and climate signal of the single existing tree‐ring chronology from the region. A tree‐ring reconstruction of wet season precipitation based on this new chronology extends from 1759–2016 and documents strong multidecadal variability that impacted the frequency of reconstruction precipitation extremes over the past 258 years. Key Points: Drought and flood extremes in the Amazon River basin have increased in frequency during the last 40 yearsA new tree‐ring chronology of Cedrela odorata confirms the dating and climate signal of a previous chronology for the eastern AmazonMultidecadal variability of tree‐ring reconstructed rainfall suggests that recent eastern Amazon rainfall extremes may not be unprecedented [ABSTRACT FROM AUTHOR]