Submitted as: model evaluation paper
09 Feb 2023
Submitted as: model evaluation paper |  | 09 Feb 2023
Status: this preprint is currently under review for the journal GMD.

Simulating heat and CO2 fluxes in Beijing using SUEWS V2020b: Sensitivity to vegetation phenology and maximum conductance

Yingqi Zheng, Minttu Havu, Huizhi Liu, Xueling Cheng, Yifan Wen, Hei Shing Lee, Joyson Ahongshangbam, and Leena Järvi

Abstract. The Surface Urban Energy and Water Balance Scheme (SUEWS) has recently been introduced to include a bottomup approach to modelling carbon dioxide (CO2) emissions and sink in urban areas. In this study, SUEWS is evaluated against radiation flux observations and eddy covariance (EC) measured turbulent fluxes of sensible heat (QH), latent heat (QE), and CO2 (FC) at a densely built neighborhood in Beijing. The model sensitivity to maximum conductance (gmax) and leaf area index (LAI) is examined. Site-specific gmax is obtained from observations over local vegetation species, and LAI parameters by optimization with remotely sensed LAI obtained from a MODIS/Terra data product. For simulation of anthropogenic CO2 components, local traffic and population data are collected. In model evaluation, the mismatch between the measurement source area and simulation domain is also considered.

Using the optimized gmax and LAI, the modelling of heat fluxes is noticeably improved, showing higher correlation with observations, lower bias, and more realistic seasonal dynamics of QE and QH. In comparison to heat fluxes, the FC module shows lower sensitivity to the choice of gmax and LAI. This can be explained by the low relative contribution of vegetation to net FC in the modelled area. SUEWS successfully reproduces the average diurnal cycle of FC and annual cumulative sums. Depending on the size of the simulation domain, the modelled annual accumulated FC ranges from 7.2 to 8.5 kg C m−2 yr−1, when compared to 7.5 kg C m−2 yr−1 observed by EC. Traffic is the dominant CO2 source, contributing 63–73 % to the annual total CO2 emissions, followed by human metabolism (14–18 %), respiration released by vegetation and soil (6–11 %) and building heating (6–9 %). Vegetation photosynthesis offsets only 4–8 % of the total CO2 emissions. We highlight the importance of choosing optimal LAI parameters and gmax when SUEWS is used to model surface fluxes. The FC module of SUEWS is a promising tool in quantifying urban CO2 emissions at the local scale, and therefore assisting to mitigate urban CO2 emissions.

Yingqi Zheng et al.

Status: open (until 01 May 2023)

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  • RC1: 'Comment on gmd-2022-305', Anonymous Referee #1, 15 Mar 2023 reply

Yingqi Zheng et al.

Data sets

Datasets for simulating heat and CO2 fluxes in Beijing using SUEWS V2020b Yingqi Zheng, Huizhi Liu, and Xueling Cheng

Yingqi Zheng et al.


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Short summary
The performance of Surface Urban Energy and Water Balance Scheme (SUEWS) is evaluated against the observed surface exchanges (fluxes) of heat and carbon dioxide in Beijing. The heat flux modelling is noticeably improved by using observed maximum conductance and by optimizing vegetation phenology modelling. SUEWS also performs well in simulating carbon dioxide flux. We believe that this study provides new insights into improving urban surface flux modelling.