Understanding the processes controlling the inter-annual variations and long-term trajectory of the tropical carbon balance remains a challenging task, largely due to uncertainties in the integrated carbon cycle responses to ENSO-dominated tropical climate variability. Ultimately, a mechanistic understanding of both climate forcings and legacy effects on ecosystem carbon cycling is needed to understand the net impact of climate variability on the tropical carbon balance. Here we use the CARbon DAta-MOdel fraMework (CARDAMOM) diagnostic model-data fusion approach—constrained by an array of satellite-based carbon cycle observations, including MODIS leaf area, biomass, OCO-2 and GOSAT solar-induced fluorescence, as well as top-down atmospheric inversion estimates of CO2 and CO surface fluxes from the NASA Carbon Monitoring System Flux (CMS-Flux)—to constrain and predict spatially-explicit tropical carbon state variables and net ecosystem carbon fluxes during 2010-2016.
Results/Conclusions
The combined constraints of land surface and atmospheric datasets in CARDAMOM yield key insights on the temperature sensitivity and the principal carbon-water feedbacks throughout the tropics and combustion factors within biomass burning regions. Our terrestrial carbon cycle analysis indicates that a quantitative disentanglement of direct forcing and memory effects is key for understanding the impact of individual ENSO events on the tropical carbon balance, and provides a critical insight on the cumulative impact of ENSO events in future projections of the tropical carbon balance. For the 2015 ENSO event, we found that (a) lagged effects amounted to a substantial component of the observed 2015 NBE anomaly, and (b) lagged effects attributable to both previous ENSO events and nominal years substantially impacted 2015 NBE. Finally, we find that the ingestion of observational constraints on the tropical water balance from satellite-based measurements of terrestrial water storage (GRACE) provide unique mechanistic insights on the trajectory of plant-available water and the role of carbon-water processes and feedbacks on the terrestrial carbon balance.