Considerable uncertainties in simulating land carbon sinks induced by different precipitation products

Precipitation, a key determinant of soil moisture variations, plays an important role in regulating terrestrial carbon fluxes on multiple time-scales. It is a critical meteorological forcing to drive terrestrial biosphere model (TBM), however, with a large uncertainty itself. We here investigated to what extent precipitation alone can cause uncertainties of model-simulated carbon flux from terrestrial ecosystems to atmosphere (F_TA), based on 8 precipitation products and a TBM, VEGAS. We find that the pattern of uncertainties in simulated F_TA obviously differs from the pattern of discrepancies in precipitation, owing to divergent water sensitivities of vegetation over different regions. Globally, the uncertainty in F_TA can be up to approximately 40.73% of the uncertainty in TRENDYv6 multi-model simulated F_TA which is caused by model structural and parameter uncertainty. A good linear relationship emerges between global area-averaged land climatological annual precipitation and simulated total F_TA with the slope of −0.0040 PgC yr⁻¹ per mm yr⁻¹ ( = 0.03; negative for carbon sink), where 70% is explained by the sensitivity over extra-tropical northern hemisphere (NH). For seasonal cycle, compared to nearly constant inter-precipitation spreads over tropics plus extra-tropical southern hemisphere (Trop+SH), uncertainties in corresponding simulated F_TA show obvious seasonal differences with the relatively larger uncertainties in March-April-May (MAM) and August-September-October (ASO). For interannual variability, uncertainties in simulated total F_TA are, albeit smaller, nonnegligible, which are 40.61% (global), 38.17% (Trop+SH), and 29.63% (NH) of the TRENDYv6 inter-model uncertainty, respectively. Therefore, generating better global precipitation product is important for reducing the uncertainty in simulating terrestrial carbon sinks.