Impact of Urban Surface Characteristics on Surface Energy Balance and CO2 Flux Based on Eddy Covariance Measurements: A Case Study of Hefei, China

Observations of energy and carbon dioxide fluxes in the urban centres of rapidly developing countries remain limited. In this study, one year of eddy covariance measurements was conducted in the city centre of Hefei to investigate how underlying urban surfaces and human activities influence surface energy and carbon dioxide fluxes. A strong correlation was observed between net radiation and sensible heat flux, with both fluxes being significantly lower in winter. Abundant summer precipitation substantially enhanced latent heat flux. Anthropogenic heat flux and storage heat flux ranged from 30 to 350 W m−2 and from −100 to 350 W m−2, respectively. Improved energy balance closure was generally associated with more unstable atmospheric conditions, while increased urban surface heterogeneity was linked to poorer closure. Traffic was identified as a major contributor to carbon dioxide emissions, with annual emissions reaching 12.73 kg CO2 m−2 yr−1 in the city centre. Carbon dioxide fluxes were significantly higher in winter and slightly lower on weekends compared to weekdays. In addition, the increasing adoption of new energy vehicles (NEVs) has contributed to a reduction in urban CO2 fluxes. Overall, human activity in urban centres substantially enhances anthropogenic heat release and carbon dioxide emissions, thereby intensifying urban heat island effects and carbon emissions.