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Impact of 2019 mid-west flood on CO2 and CH4 using yearly WRF-GHG simulations over the contiguous United States
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  • Xiao-Ming Hu,
  • Ming Xue,
  • Lan Gao,
  • Sean Crowell
Xiao-Ming Hu
University of Oklahoma Norman Campus

Corresponding Author:[email protected]

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Ming Xue
Univ Oklahoma
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Lan Gao
University of Oklahoma Norman Campus
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Sean Crowell
University of Oklahoma
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Sources and sinks of the two most important greenhouse gases CO2 and CH4 at regional to continental scales remain poorly understood. In our previous work, the WRF-VPRM, a weather-biosphere-online-coupled model in which the biogenic CO2 fluxes are handled by the Vegetation Photosynthesis and Respiration Model (VPRM), was further developed by coupling with the CarbonTracker global CO2 simulation and incorporating optimized terrestrial CO2 flux parameterization (Hu et al., 2021; Hu et al., 2020). In this work, an enhanced version of WRF-VPRM by including CH4 (referred to as WRF-GHG hereafter) is further developed by coupling with the Copernicus Atmosphere Monitoring Service (CAMS) CH4 global simulation for the initial and boundary conditions and the WetCHARTs wetland CH4 emissions and NEI2017 anthropogenic CH4 emissions, which dominate emissions over the contiguous United States (CONUS). Yearly WRF-GHG simulations are conducted for year 2018 and 2019 over CONUS at a horizontal grid spacing of 12 km to examine the impact of 2019 abnormal mid-west precipitation on CO2 and CH4 fluxes and atmospheric concentrations, with the simulation for 2018 serving as a baseline for comparison, similarly to Yin et al (2020). Simulated CO2 and CH4 are evaluated using remotely sensed data from Total Carbon Column Observing Network (TCCON), OCO-2, TROPOMI, and in-situ measurements from the GLOBALVIEW obspack data. WRF-GHG has been shown to capture the monthly variation of column-averaged CO2 concentrations (XCO2) and episodic variations associated with frontal passages. In this work, we will show that TCCON XCH4 shows mild seasonal variation and more prominent episodic variations, which are captured by WRF-GHG. As a case study, the 2019 May flood delayed growing season in mid-west and the typical spring and summer drawdown of atmospheric CO2 by 1-3 weeks. Obspack and TROPOMI data indicate higher CH4 in the mid-west in July and August, in 2019 relative to 2018, which we hypothesize is related to the abnormal precipitation in 2019 in the region that induces more wetland CH4 emissions. The WRF-GHG model significantly underestimates CH4 concentration in mid-west in summer 2019 when the WetCHARTs wetland CH4 emissions are driven by ERA-Interim reanalysis precipitation, which is known to be underestimated. An updated WetCHARTs wetland CH4 emissions driven by the PRISM precipitation data are currently being produced at JPL, which are expected to reduce the WRF-GHG CH4 bias, as wetland fluxes are highly sensitive to inundation from precipitation.