Terrestrial CO₂ Fluxes, Concentrations, Sources and Budget in Northeast China: Observational and Modeling Studies

Abstract

CO2 fluxes and concentrations are not well understood in Northeast China, where dominant land surface types are mixed forest and cropland. Here, we analyzed the CO2 fluxes and concentrations using observations and the Weather Research and Forecasting model coupled with the Vegetation Photosynthesis and Respiration Model (WRF‐VPRM). We also used WRF‐VPRM outputs to examine CO2 transport/dispersion and budgets. Finally, we investigated the uncertainties of simulating CO2 fluxes related to four VPRM parameters (including maximum light use efficiency, photosynthetically active radiation half‐saturation value, and two respiration parameters) using off‐line ensemble simulations. The results indicated that mixed forests acted as a larger CO2 source and sink than rice paddies in 2016 due to a longer growth period and stronger ecosystem respiration, although measured minimum daily mean net ecosystem exchange (NEE) was smaller at rice paddy (−10 μmol·m‐2·s‐1) than at mixed forest (−6.5 μmol·m‐2·s‐1) during the growing season (May–September). The monthly fluctuation of column‐averaged CO2 concentrations (XCO2) exceeded 10 ppm in Northeast China during 2016. The large summertime biogenic sinks offset about 70% of anthropogenic contribution of XCO2 in this region. WRF‐VPRM modeling successfully captured seasonal and episodic variations of NEE and CO2 concentrations; however, NEE in mixed forest was overestimated during daytime, mainly due to the uncertainties of VPRM parameters, especially maximum light use efficiency. These findings suggest that the WRF‐VPRM modeling framework will provide greater understanding of the natural and anthropogenic contributions to the carbon cycle in China, especially after calibration of parameters that control biogenic fluxes.

Implementation of Improved Parameterization of Terrestrial Flux in WRF‐VPRM Improves the Simulation of Nighttime CO2 Peaks and a Daytime CO2 Band Ahead of a Cold Front

“…Afternoon minimum CO 2 shows a prominent seasonal cycle with minimum in July-August at WBI crop site and in June-September at LEF, AMT mixed forest sites (Figure 3), consistent with previous studies (Bakwin et al, 1998;Parazoo et al, 2008), indicating active terrestrial uptake in growing season during daytime. Note that mixed forest typically has a longer growing season than crop (Li et al, 2020 (Hu, Crowell, Wang, Zhang, et al, 2020), both of which only have daytime observations. Relatively less-reported is the seasonal variation of nighttime CO 2 peaks/spikes (e.g., Bakwin et al, 1998;Davis et al, 2003), which increase significantly during growing seasons (Figure 3).…”

Multisensor and Multimodel Monitoring and Investigation of a Wintertime Air Pollution Event Ahead of a Cold Front Over Eastern China

“…The WRF-CO 2 simulation conducted in this work follows a similar configuration used by our previous studies (Hu et al, 2020;, but applying over a different domain configuration in this study (a 20-km grid spacing in the first domain and a 4-km grid spacing in the second domain, Figure 1, same as WRF-Chem). Different from the WRF-Chem simulation, which spans for the selected pollution episode, the WRF-CO 2 simulation is only a segment of a yearly downscaling simulation that uses spectral nudging to maintain the large scale forcing in the simulation domain (see Hu et al (2020) and Li et al (2020) for details). Thus, the CO 2 simulation for the selected December 9 episode has been spun-up for 11 months.…”

Daily Model of Xco2 Based on Orbital Observations for the State of São Paulo – Brazil

“…Several studies con rm that photosynthesis is the main regulator of atmospheric carbon sinks [10,24,25,26]. However, photosynthesis is a process sensitive to climatic variations such as relative humidity [27], precipitation [28], evapotranspiration [29], and incident solar irradiance [30].…”