Partitioning Climatic Controls on Global Land Carbon Sink Variability: Temperature vs. Moisture Constraints Across Biomes

Terrestrial carbon sink has exhibited significant interannual variability (IAV) over the past five decades. However, the dominant regions and factors controlling the IAV of global land carbon sink remain controversial. Using six TRENDY models, we quantified regional contributions to the IAV of global land carbon sink from 1981 to 2017 and identified the dominant factors across different ecosystems and the globe. Results indicated that forests and savannas contributed most to global net biome productivity (NBP) IAV (27% and 29%, respectively). Further analyses revealed that root zone soil moisture (RZSM) and vapor pressure deficit (VPD) played a dominant role at the local and global scales, particularly in regions between 20° S and 40° S and 40° N–60° N. Across different ecosystems, the dominant drivers of NBP IAV varied greatly. More precisely, in tropical forests, NBP IAV was dominated by temperature variability, whereas in extra-tropical forests and croplands, VPD variability played a dominant role. Furthermore, in shrublands and grasslands, RZSM and VPD have comparable effects on NBP anomalies. Our findings provided robust evidence for an important joint control of RZSM and VPD in the IAV of land carbon sink, and reduced some of the uncertainty around the dominant drivers of temporal variability in NBP.