Summertime surface energy balance fluxes at two Beijing sites

Abstract

Summertime (June–August 2015) radiative and turbulent heat fluxes were measured concurrently at two sites (urban and suburban) in Beijing. The urban site has slightly lower incoming and outgoing shortwave radiation, lower atmospheric transmissivity and a lower surface albedo than the suburban site. Both sites receive similar incoming longwave radiation. Although the suburban site had larger daytime outgoing longwave radiation (L↑), differences in the daily mean L↑ values are small, as the urban site has higher nocturnal L↑. Overall, both the midday and daily mean net all‐wave radiation (Q*) for the two sites are nearly equal. However, there are significant differences between the sites in the surface energy partitioning. The urban site has smaller turbulent sensible heat (Q H) (21–25% of Q* [midday–daily]) and latent heat (Q E) fluxes (21–45% of Q*). Whereas, the suburban proportions of Q* are Q H 32–32% and Q E 39–66%. The daily (midday) mean Bowen ratio (Q H/Q E) was 0.56 and 0.49 (0.98 and 0.83) for the urban and suburban sites, respectively. These values are low compared with other urban and suburban areas with similar or larger fractions of vegetated cover. Likely, these are caused by the widespread external water use for road cleaning/wetting, greenbelts, and air conditioners. Our suburban site has quite different land cover to most previous suburban studies as crop irrigation supplements rainfall. These results are important in enhancing our understanding of surface–atmosphere energy exchanges in Chinese cities and can aid the development and evaluation of urban climate models and inform urban planning strategies in the context of rapid global urbanization and climate change.