## 2 Datasets and Pre-Processing Steps
### XCO\({}_{2}\) from Model Simulations  
We also compared the results from CarbonTracker 2016. CarbonTracker is a model-data assimilation system and annual updates provide atmospheric CO\({}_{2}\) mixing ratio distributions and \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Data** & **Source** & **Space Res.** & **Time Res.** & **Reference** \\ \hline GM-XCO\({}_{2}\) & Mapping data from ACOS GOSAT v7.3 & 1.0 \(\times\) 1.0 de. & 3 days & \
\begin{tabular}{c} [PERSON] et al. [33] \\ [PERSON] et al. [28] \\ \end{tabular} \\ \hline CT-XCO\({}_{2}\) & CarbonTracker 2016 & 2.0 \(\times\) 3.0 de. & 3 h & [PERSON] et al. [50] \\ \hline GEOS-XCO\({}_{2}\) & GEOS-Chem v11.1 & 2.0 \(\times\) 2.5 de. & 3 h & [PERSON] et al. [51] \\ \hline SiB3 CO\({}_{2}\) flux & Simple Biosphere Model, version 3 & 1.0 \(\times\) 1.25 de & 3 h & [PERSON] et al. [52] \\ \hline Temp & AIRSX3 STM v6.0, produced with AIRS and AMBU & 1.0 \(\times\) 1.0 de. & monthly & [PERSON] et al. [53] \\ \hline scPDSI & CRU TS 3.25 & 0.5 \(\times\) 0.5 de. & monthly & [PERSON] et al. [54] \\ \hline BA & GFED v4.0 & 0.25 \(\times\) 0.25 de. & monthly & [PERSON] et al. [55] \\ \hline GPP & MODI7A2 v5 & 1.0 \(\times\) 1.0 km & monthly &
\begin{tabular}{c} [PERSON] et al. [56]; \\ [PERSON] et al. [57] \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of the datasets used in this study. XCO\({}_{2}\) from global mapping of satellite observations (GM-XCO\({}_{2}\)) and model simulation (CarbonTracker: CT-XCO\({}_{2}\) and GEOS-Chem (described in Section 2.2)): GEOS-XCO\({}_{2}\)), biospheric CO\({}_{2}\) fluxes from SiB3 used in GEOS-Chem, environmental parameters including surface skin temperature (Temp), self-calibrating Palmer drought severity index (scPDSI), burned area (BA), and gross primary production (GPP). The spatial and temporal resolution of the observations or model products are indicated as well as a reference describing the products in more detail. inferred surface fluxes [50]. CarbonTracker uses the Carnegie-Ames-Stanford Approach (CASA) land surface model to estimate priors and Transport Model 5 (TM5) to represent atmospheric circulation [58]. CarbonTracker version 2016 provide atmospheric CO\({}_{2}\) concentration from 1 January 2009 to 31 December 2015 [59]. We calculated the XCO\({}_{2}\) from the CarbonTracker atmospheric distribution of CO\({}_{2}\) (CT-XCO\({}_{2}\)), with spatial resolution of 2 \(\times\) 3 degrees and time resolution of 3 days, using the CO\({}_{2}\) profile data within the local time around 13:00, with the pressure-averaged method described in [PERSON] et al. [60]. After that, CT-XCO\({}_{2}\) was downscaled to be 1 \(\times\) 1 degrees using the nearest neighbor. We tested the sensitivity of XCO\({}_{2}\) to changes in surface fluxes using a collection of surface flux estimates and the GEOS-Chem global chemical transport model (CTM) assimilated with meteorological fields from the National Aeronautics and Space Administration (NASA) Goddard Earth Observing System (GEOS) [51; 61]. Surface CO\({}_{2}\) fluxes used in GEOS-Chem include fossil fuel emission from Open-source Data Inventory for Anthropogenic CO\({}_{2}\) (ODIAC); biomass burning from the Global Fire Emission Database (GFED3); ocean exchange from [PERSON] et al. [62] and annual biofuel fluxes from Yevich and Logan [63]. Biospheric CO\({}_{2}\) fluxes used for this simulation were from the SiB3 [52]. The biospheric fluxes from SiB3 were not available for our entire study period (only 2006 through 2010), therefore, we only use them as a way to test the influence of atmospheric transport on extreme XCO\({}_{2}\) detection. In order to calculate the extreme XCO\({}_{2}\) detection from the GEOS-Chem sensitivity test, we did need to use biospheric flux estimates for the entire record. For this purpose, we used only 2009 flux repeated from 2010 to 2015. This was important for determining the Z score (described in Section 3.2) of the GEOS-Chem simulation.