Interannual variations in terrestrial carbon uptake are dominated by temperature and the vapor pressure deficit rather than water availability

Abstract

Interannual variations in terrestrial carbon uptake (IVTCU) strongly regulate anthropogenic CO₂ growth rate dynamics, yet their controlling mechanisms remain uncertain. Previous studies disagree on whether precipitation (P) or temperature (T) predominates and whether soil moisture (SM) or vapor pressure deficit (VPD) is the primary driver. Using ground-based meteorological observations and remotely sensed gross carbon uptake data (1982–2016), we reveal that the global IVTCU is controlled by T and VPD, whereas the influences of water availability (P or SM) are relatively weak. Regionally, the VPD exerts dominant control in arid areas and common drought-adapted ecosystems, whereas T predominates in other regions, especially cold areas. In contrast to the prevailing view that water availability constrains carbon uptake in arid systems, our analysis reveals that although P yields greater influences in these regions than elsewhere, the VPD remains the main factor limiting the IVTCU. This highlights the notable inhibitory effect of atmospheric dryness on arid ecosystem carbon uptake. Globally, the sensitivity of the IVTCU to T is greatest between 7 °C and 16 °C and decreases rapidly at higher T, where the VPD gradually becomes the dominant factor. The IVTCU responds less strongly to the VPD than to T, but the VPD maintains a substantial influence, especially below 10 hPa. Both the sensitivity and threshold vary across land cover/climate zones. These findings refine our understanding of the mechanisms driving carbon flux variability, challenge conventional assumptions regarding arid-region controls, and provide critical insights for improving land–atmosphere coupling models under a changing climate.