[A-AS08] Atmospheric Chemistry

[AAS08-P03] High resolution CO₂ simulation around the Takayama forest in central Japan

*Asaka Hasegawa^1,2, Ryoichi Imasu¹, Yousuke Sato³, Qiao Wang¹, Yutaka Arai¹, Shohei Murayama^2,4, Hiroaki Kondo², Shigeyuki Ishidoya², Takahisa Maeda² (1.Atmosphere and Ocean Research Institute, The University of Tokyo, 2.National Institute of Advanced Industrial Science and Technology, 3.Graduate School of Engineering, The University of Osaka, 4.Dokkyo University)

Keywords:

Carbon dioxide,CO2 flux,Atmospheric transport model,Terrestrial Ecosystem model

Achieving carbon neutrality requires an objective evaluation method of decarbonization technologies and policies. Inverse analysis enables the estimation of CO₂ emissions and uptake by combining an atmospheric transport model with observations. Because this approach relies on observational data, it provides a more objective estimate of CO₂ inventory compared with bottom-up inventories. According to IPCC (2022), CO₂ emissions from urban areas represent approximately 70% of global emissions. A high-resolution atmospheric transport model, capable of simulating at 1km or finer resolution, is required to estimate CO₂ transport and flux within urban areas. When estimating CO₂ fluxes in metropolitan areas such as Tokyo metropolitan region, it is necessary to consider not only anthropogenic emissions but also biogenic fluxes from suburban forests. To estimate anthropogenic CO₂ fluxes in regions where various emission and uptake sources coexist, it is essential to first understand CO₂ fluxes and concentration variations over the area where vegetation is the dominant source of CO₂ exchange. In this study, we focused on biogenic CO₂ fluxes and simulated CO₂ concentration distributions around the forest using a terrestrial ecosystem model and a high-resolution atmospheric transport model. Few studies have evaluated CO₂ distributions around forested areas in Japan using these high-resolution models.
Our target site is Takayama (TKY) in Gifu Prefecture, located in central Japan. At this site, CO₂ fluxes, CO₂ concentrations, and meteorological variables are observed at and around a flux tower (Murayama et al., 2024). We calculated hourly CO₂ concentration variations during the growing season with SCALE-RM-CO₂ (Sato et al., 2025). The calculation resolutions range from 10 km to 1 km using offline nesting. Both anthropogenic and natural fluxes were prepared as at a 1 km resolution, based on EAGrid 2000-Japan (Kannari et al., 2007) and the terrestrial ecosystem model, BEAMS-diurnal (Wang et al., 2021), respectively. This 1 km fluxes dataset was aggregated to match the resolution of each transport calculation. We first evaluated the performance of BEAMS-diurnal in reproducing observed CO₂ fluxes at this site. BEAMS-diurnal captures the diurnal variation of gross primary production satisfactorily, but its amplitudes of ecosystem respiration are larger than those in the observations. SCALE-RM-CO₂ reproduced the seasonal and diurnal variations, as well as the monthly mean CO₂ concentrations, reasonably well at this site. The correlation between the model results and observations was about 0.6 for 1 km resolution for August 2016. In the presentation, we will also show the comparison results between the models and observations for other months, as well as analyses of local CO₂ transport considering the complex terrain around this site.