Search

Extreme climate events are becoming more frequent, with poorly understood implications for carbon sequestration by terrestrial ecosystems. A better understanding will critically depend on accurate and precise quantification of ecosystems responses to these events. Taking the 2019 US Midwest floods as a case study, we investigate current capabilities for tracking regional flux anomalies with “top‐down” inversion analyses that assimilate atmospheric CO2observations. For this analysis, we develop a regionally nested version of the NASA Carbon Monitoring System‐Flux system for North America (CMS‐Flux‐NA) that allows high resolution atmospheric transport (0.5° × 0.625°). Relative to a 2018 baseline, we find the 2019 US Midwest growing season net carbon uptake is reduced by 11–57 TgC (3%–16%, range across assimilated CO2data sets). These estimates are found to be consistent with independent “bottom‐up” estimates of carbon uptake based on vegetation remote sensing (15–78 TgC). We then investigate current limitations in tracking regional carbon budgets using “top‐down” methods. In a set of observing system simulation experiments, we show that the ability of atmospheric CO2inversions to capture regional carbon flux anomalies is still limited by observational coverage gaps for both in situ and satellite observations. Future space‐based missions that allow for daily observational coverage across North America would largely mitigate these observational gaps, allowing for improved top‐down estimates of ecosystem responses to extreme climate events. Extreme climate events, such as floods or heatwaves, can have major impacts on the carbon cycle. For example, widespread flooding in the US Midwest during 2019 delayed the planting of crops leading to reduced plant growth and carbon uptake relative to 2018. Here, we test how well this reduction in carbon uptake can be inferred from measurements of atmospheric CO2. We find that these data can identify reduced net carbon uptake to the US Midwest during the 2019 floods, but that sparse observational coverage limits our ability to quantify the anomaly in net carbon uptake. We show that expanded space‐based observations of CO2would fill these gaps, allowing for improved estimates of interannual variations in the US CO2budget. Bottom‐up and top‐down methods capture reduced 2019 US Midwest carbon uptake relative to 2018Gaps in atmospheric CO2observations drive uncertainties in top‐down estimatesNested inversion better localizes US Midwest ΔNEE relative to coarse global model Bottom‐up and top‐down methods capture reduced 2019 US Midwest carbon uptake relative to 2018 Gaps in atmospheric CO2observations drive uncertainties in top‐down estimates Nested inversion better localizes US Midwest ΔNEE relative to coarse global model