This repository is supplementary to the paper "Sun, Y., Oleson, K. W., & Zheng, Z. (2026). Modeling urban traffic heat flux in Community Earth System Model: Formulation and validation for two test sites. Journal of Advances in Modeling Earth Systems, 18, e2025MS005435. https://doi.org/10.1029/2025MS005435". A related dataset is open access at: https://doi.org/10.6084/m9.figshare.31891603.
The objectives of this project are:
- Modify the CESM source code to incorporate an urban traffic heat flux module for quantifying anthropogenic heat flux (AHF);
- Validate model performance with the new traffic module at two test sites;
- Examine traffic-induced thermal impacts on the urban environment and building energy use.
The standard source code comes from CTSM, with the release tag: ctsm5.3.024. See modified code lines labeled with !YS.
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Create a new module to read time-varying traffic data and provide traffic-related functions:
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Calculate the impervious road width and number of lanes:
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Pass traffic inputs to compute the traffic heat flux:
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Add the module in the model initialization and computation processes:
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Add time-varying input data to the namelists:
We conducted a pair of single-point simulations (CNTL and TRAF) at the Capitole of Toulouse, France (FR-Capitole), and Manchester, UK (UK-Manchester).
- FR-Capitole
- SourceMods: code used at FR-Capitole simulations with additional modifications to use local parameters.
- datm_files: atmospheric forcing data, derived from the Urban-PLUMBER.
- input_files: surface data, derived from the Urban-PLUMBER and UTC19 traffic dataset.
- UK-Manchester
- SourceMods: code used at UK-Manchester simulations.
- datm_files: atmospheric forcing data from bias-corrected ERA5-Land reanalysis data.
- input_files: surface data from the CTSM's default land surface dataset and Transport for Greater Manchester (TfGM)
The scripts listed below are used to visualize two sites with corresponding traffic diurnal cycles.
| Num. | Subject | Data process | Visualization |
|---|---|---|---|
| 3.1 | Metadata at FR-Capitole | Use Export.ipynb to get the diurnal mean vehicle volume | Figure.ipynb |
| 3.2 | Metadata at UK-Manchester | Use Export.ipynb to get the diurnal mean vehicle volume | Figure.ipynb |
The scripts listed below process CNTL (urban_traffic=.false.) and TRAF (urban_traffic=.true.) simulation output and visualization.
| Num. | Subject | Output data process | Visualization |
|---|---|---|---|
| 3.3 | Model validation at FR-Capitole | Use Export.ipynb to get monthly mean and hourly mean variables in comparison with observations | Figure.ipynb |
| 3.4 | Anthropoegnic heat at FR-Capitole | Use Export.ipynb to get monthly mean and hourly mean variables related to AHF | Figure.ipynb |
| 3.5 | Model validation at UK-Manchester | Use Export.ipynb to get monthly mean and hourly mean variables in comparison with observations | Figure.ipynb |
| 3.6 | Heat stress at UK-Manchester | Use Export.ipynb to get heat stress indices | Figure.ipynb |
| 3.7 | Compare temperatures | Use Export.ipynb to get the difference in temperature between TRAF and CNTL simulations | Figure.ipynb |
| 3.8 | Model sensitivity at FR-Capitole | Use Export.ipynb to export Taylor Diagram metrics | Figure.ipynb |
| 3.9 | Model sensitivity at UK-Manchester | Use Export.ipynb to export changes due to traffic parameter perturbation | Figure.ipynb |
The figures listed below are used to illustrate the details of the model workflow and mechanism.
| Subject | Visualization |
|---|---|
| Timeline of incorporating AHF in global simulation | Figure |
| Workflow of incorporating urban traffic modeling in CTSM | Figure |
| Biogeophysical mechanism of traffic-induced thermal effects | Figure |
| Traffic-induced changes in heat flux and temperatures at FR-Capitole | Figure |
| Traffic-induced changes in heat flux and temperatures at UK-Manchester | Figure |
| Community Land Model | Figure |
| Future work | Figure |
The scripts listed below show supplementary information such as input data and simulation results.
| Num. | Subject | Analysis | Visualization |
|---|---|---|---|
| 5.1 | Global number of lanes | Use Export.ipynb to export the global number of traffic lanes | Figure.ipynb |
| 5.2 | Computational cost | Use Export.ipynb to describe computational timing | Figure.ipynb |
Note:
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We also provide [supporting information](./5_supplementary_information/2025ms00543-sup-0001-supporting information si-s01.docx) along with the journal article.
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Based on the model development, future work could be as follows:
- This work was supported by the Natural Environment Research Council [grant number UKRI1294], and the UKRI Harmonised Impact Acceleration Account, funded via the Economic & Social Research Council [grant number ES/X004759/1] and Engineering & Physical Sciences Research Council [grant number EP/X525753/1].
- This work used the ARCHER2 UK National Supercomputing Service and JASMIN, the UK’s collaborative data analysis environment.
- We gratefully acknowledge Transport for Greater Manchester (TfGM) for providing traffic data to support this research.
- We appreciate Dr. Xiaodan Xu from Lawrence Berkeley National Laboratory for her valuable insights.
- Z. Z. appreciates the support provided by the academic start-up funds from the Department of Earth and Environmental Sciences at The University of Manchester.
- Y. S. is supported by Zhonghua Zheng's academic start-up funds.
- Contributions from K. W. O. are based upon work supported by the NSF National Center for Atmospheric Research, which is a major facility sponsored by the U.S. National Science Foundation under Cooperative Agreement No. 1852977.
- The authors declare no conflict of interest.