Enhanced carbon flux response to atmospheric aridity and water storage deficit during the 2015-2016 El Niño compromised carbon balance recovery in tropical South America

During the 2015-2016 El Niño, the Amazon basin released almost one gigaton of carbon (GtC) into 52 the atmosphere due to extreme temperatures and drought. The link between the drought impact and 53 recovery of the total carbon pools and its biogeochemical drivers is still unknown. With satellite54 constrained net carbon exchange and its component fluxes including gross primary production and 55 fire emissions, we show that the total carbon loss caused by the 2015-2016 El Niño had not 56 recovered by the end of 2018. Forest ecosystems over the Northeastern (NE) Amazon suffered a 57 cumulative total carbon loss of ~0.6 GtC through December 2018, driven primarily by a suppression 58 of photosynthesis whereas southeastern savannah carbon loss was driven in part by fire. We 59 attribute the slow recovery to the unexpected large carbon loss caused by the severe atmospheric 60 aridity coupled with a water storage deficit during drought. We show the attenuation of carbon 61 uptake is three times higher than expected from the pre-drought sensitivity to atmospheric aridity 62 and ground water supply. Our study fills an important knowledge gap in our understanding of the 63 unexpectedly enhanced response of carbon fluxes to atmospheric aridity and water storage deficit 64 and its impact on regional post-drought recovery as a function of the vegetation types and climate 65 perturbations. Our results suggest that the disproportionate impact of water supply and demand 66 could compromise resiliency of the Amazonian carbon balance to future increasesin extreme events