Hydrologic limitations on tropical terrestrial carbon fluxes in a model-data fusion framework

Abstract:

Drought stress plays an important role in tropical terrestrial ecosystems, but its impact on the net CO₂ exchange with the atmosphere is highly uncertain. Here, we use satellite-derived observations of terrestrial water storage (TWS, the integral of the net water flux) from the GRACE mission and net biome exchange (NBE) from the CMS-Flux platform as constraints in a data assimilated model of the tropical land surface from 2001–2018. We find that by including GRACE as a constraint on TWS, we reduce the uncertainty in the modeled hydrologic cycle, and increase the occurrence of water limitations to the carbon cycle. Our observationally constrained reanalysis indicates where, when, and by how much water availability modulates both the mean state and the interannual variability of NBE. Sensitivity of NBE to perturbed hydrologic input suggests how ecosystems could potentially respond to drought stress under changes to climatic conditions. We find that the instantaneous response of plant growth to drought stress reduces the total tropical land carbon sink by 1.22 Pg carbon per year over the study period.