the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Urban Weather Modeling using WRF: Linking Physical Assumptions, Code Implementation, and Observational Needs
Abstract. The Weather Research and Forecasting (WRF) model includes urban schemes that simulate the influence of urban surfaces on the atmosphere using parameterizations for flux, and radiative exchanges. Three core schemes – the Bulk urban parameterization, Single-Layer Urban Canopy Model (SLUCM), and Multi-Layer Urban Canopy Model (MLUCM) – represent increasing levels of complexity. Although the parameterizations within these urban schemes are described in the literature, their specific implementation remains poorly documented, thus slowing down model development efforts.
This manuscript provides a roadmap to the three urban schemes in WRF version 4.5.2, presenting equations using the same symbols as in the model code, along with references to code lines, and including graphics and explanations that connect the code to its physical foundations. Our thorough review of the urban parameterizations implemented in WRF version 4.5.2 highlighted a handful of parameters that may introduce discontinuities in simulations: (i) in the SLUCM, a 1 mm/hr rain rate threshold is employed to switch between two minimum moisture availability parameterizations, thus impacting latent heat flux calculations; (ii) in the SLUCM a threshold is used to partition shortwave radiation into direct and diffuse components; (iii) in all three urban schemes, the bulk Richardson number is employed to select the similarity function, which influences the vertical distribution of heat and momentum. We also identified a highly simplified treatment of the radiative balance on roof surfaces. The implications of these simplifications can be assessed through targeted observations across relevant conditions, including varying precipitation rates, cloud cover, and transitions between stability regimes. Furthermore, the widespread application of the Monin-Obukhov similarity theory in these urban schemes warrants model evaluation under highly stable and unstable conditions and in heterogeneous urban settings with variable land cover and building heights on scales finer than model resolution. To address these challenges, we offer guidance on observational strategies, emphasizing the need for multi-parametric measurements to capture potential compensating biases and multi-height measurements that align with the levels where quantities are diagnostic and prognosed in the model (i.e., the lowest atmospheric level of the WRF model). Finally, our inspection of the code revealed implementation bugs that have now been corrected in WRF versions 4.6.0 and 4.6.1. Sensitivity tests over the Atlanta urban area show that these corrections affect surface temperatures, underscoring the importance of performing rigorous documentation and verification of the implementation of parameterizations in model code.
Competing interests: One of the authors is a member of the editorial board of Geoscientific Model Development. The authors declare that they have no other competing interests.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: closed
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RC1: 'Comment on egusphere-2025-1751', Anonymous Referee #1, 23 Jun 2025
- AC1: 'Reply on RC1', Parag Joshi, 01 Aug 2025
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RC2: 'Comment on egusphere-2025-1751', Lucas Harris, 01 Jul 2025
This manuscript is a rare example of both a useful technical reference comparing actual implemented schemes in a numerical model, getting down to the individual symbols defined in the code, and informed scientific commentary and recommendations. I have a number of minor concerns, but otherwise the paper should be published. See my attached report.
- AC2: 'Reply on RC2', Parag Joshi, 01 Aug 2025
Status: closed
-
RC1: 'Comment on egusphere-2025-1751', Anonymous Referee #1, 23 Jun 2025
- AC1: 'Reply on RC1', Parag Joshi, 01 Aug 2025
-
RC2: 'Comment on egusphere-2025-1751', Lucas Harris, 01 Jul 2025
This manuscript is a rare example of both a useful technical reference comparing actual implemented schemes in a numerical model, getting down to the individual symbols defined in the code, and informed scientific commentary and recommendations. I have a number of minor concerns, but otherwise the paper should be published. See my attached report.
- AC2: 'Reply on RC2', Parag Joshi, 01 Aug 2025
Data sets
ERA5 Reanalysis (0.25 Degree Latitude-Longitude Grid) European Centre for Medium-Range Weather Forecasts https://doi.org/10.5065/BH6N-5N20
WRF urban canopy models simulations dataset Tzu-Shun Lin et al. https://doi.org/10.5281/zenodo.15191965
Model code and software
A Description of the Advanced Research WRF Model Version 4.3 W. C. Skamarock et al. https://github.com/wrf-model/WRF/releases
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