Fig. 2: Partitioning methods underestimate pulse event CO2 fluxes.
From: Widespread underestimation of rain-induced soil carbon emissions from global drylands
a, Contributions of ecosystem respiration (Reco) and NEP during pulse events to annual Reco and NEP. Pulse event contribution (%) at each individual site is calculated as \(\frac{{{\mathrm{sum}}}\left(x\right)}{{{\mathrm{sum}}}\left(\,y\right)}\times 100\), in which x is FluxPulse bias-corrected half-hourly Reco or NEP during pulse events, and y is all available half-hourly bias-corrected Reco or NEP (two sites whose NEP contribution values greater than three times of standard deviation were removed in the boxplots for visualization purposes). b, Performance of partitioning methods on estimating ecosystem respiration (Reco) and GPP during pulse events. The fluxes estimated from four methods were compared with the FluxPulse bias-corrected Reco and GPP, which are the night-time (NT) method, the daytime method (DT), DML and NN (Methods). The flux underestimation is calculated as \(\frac{{{\mathrm{sum}}}\left(x\right)-{{\mathrm{sum}}}(\;y)}{{{\mathrm{sum}}}\left(x\right)}\times 100\), in which x is the FluxPulse half-hourly Reco or GPP and yis the partitioned half-hourly Reco or GPP from different partitioning methods. Thus, the positive yvalues indicate flux underestimations, while negative yvalues indicate flux overestimations. In a and b, 28/34 sites whose FluxPulse significantly reduces biases (P < 0.001) (Extended Data Fig. 6) are included. The boxes represent interquartile range (IQR) marked with 25th, 50th and 75th percentile and whiskers extending to 1.5 times the IQR. The red diamonds represent the mean of the boxplots. In b, all the boxplots have the mean of distribution statistically greater than 0 (one-tailed paired t-test, P < 0.01). c, Half-hourly time series visualization of NEE, ecosystem respiration estimated by the FluxPulse bias-corrected algorithm (FluxPulse Reco) and by the NT method Reco at the Albuera site, Spain (ES-Abr) in 2017. The NEE points corresponding to pulse events are manually labelled in green, while others are labelled in black. The red line represents FluxPulse bias-corrected Reco, and the blue line represents Reco estimated by the NT method. In the lower graph, the black line shows the daytime EF, calculated daily. The blue bars are precipitation downscaled from ERA-Interim reanalysis data products, with half-hourly resolution. A sharp rise in EF and increased precipitation indicates the occurrence of pulse events and net CO2 pulses.
