Short Term Effects of 2019 Early Summer Floods on Atmospheric CO2 in the Midwestern and Southern Regions of the United States as Seen from the NASA GEOS Model

Studies show that climate extremes add considerable variability to the global year-to-year increase in atmospheric CO₂ through their influence on terrestrial ecosystems. These extremes are characterized by meteorological phenomena such as droughts, floods, heat waves, frosts, and windstorms. While the impact of droughts on terrestrial ecosystems has received considerable attention in the past, the response to extreme flooding events is poorly understood. To improve upon such understanding, we investigate how the spring/early summer midwestern and southern US flooding events of 2019 affected regional atmospheric CO₂ mole fractions. In our analyses, we simulate CO₂ with NASA's Global Earth Observing System (GEOS) model, where fluxes of CO₂ are typically estimated based on a suite of remote sensing observations including greenness, night lights, and fire radiative power. As a starting point for this investigation of 2019, GEOS simulations make use of flux distributions that use spatial climatology derived from previous years. This type of formulation does not include the year-specific response to flooding, thus allowing us to use available in situ CO₂ observations (including three towers located in Iowa, Mississippi, and Florida and two campaigns, the airborne Atmospheric Carbon and Transport (ACT) - America 2019 and the shipboard Satellite Coastal and Oceanic Atmospheric Pollution Experiment (SCOAPE)), to estimate Net Biome Exchange (NBE) anomalies in the regions of interest by assuming that mismatches between the model and observations can be at least partly attributed to the flooding of 2019. Preliminary results indicate that in the Midwest (mainly consists of crops such as corn and soybeans), flooding contributed to about 20% reduction of NBE in May-June 2019 and to about 10% enhancement of NBE in July 2019, which is consistent with independent reports of changes in agricultural activity. In the south (mainly forests), we hypothesize that the flooding early in the growing season contributed to NBE enhancement in May. These results demonstrate the importance of better understanding the impact of flooding events on terrestrial ecosystems.