EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regional modeling of urban climate: the impact of physical process representation

Peter Huszár1, Jan Karlický1, jana Ďoubalová1,2, Tereza Nováková1, Filip Švábik1, Michal Belda1, and Tomáš Halenka1
Peter Huszár et al.
  • 1Charles University, Faculty of Mathematics and Physics, Dept. of Atmospheric Physics, 18200, Prague 8, Czechia (
  • 2Czech Hydrometeorological Institue, Na Šabatce 2050/17, 143 06 Prague 4, Czechia

The urban heat island (UHI) is a relaively old concept and has been widely studied using both observational and modeling approches. However, urban canopies impact the meteorological conditions in the planetary boundary layer (PBL) and above in many other ways, e.g. urban breeze circulation can form, enhanced drag causes intensification of the turbulent diffusion leading to elevated PBL height, reduced evaporation results in decreased absolute humidity, changes in cloudiness etc.
A well established regional model representation of these phenomena is crucial for both mitigation and adaptation in areas affected by intense urbanization and climate change. There are however large uncertainities how the underlying physical processes are represented in numerical models, i.e. what models are used along with which parameterizations and parameters.

Here we perform a regional multi-model analysis over central Europe using the Regional Climate Model (RegCM4) and Weather Research and Forecast (WRF) regional models with different configurations representing different PBL treatment, convection parameterization, surface layer physics, microphysics and urban canopy models. Model results are extensively compared to surface measurements as well as satellite observation of surface temperatures. We analyse the model results mainly in terms of the urban-rural contrast which is a measure of the difference between the urban core value and the vicitinity (with respect to the particular city) for selected meteorological parameters. Our results show substantial impact of the choice of the model as well as the choice of parameterization on the intensity of UHI and other meteorological effects. The urban-rural difference of PBL height and average wind speed between urban areas and their vicinity is affected the most, controlled by the boundary layer physics parameterization.
Our simulations confirm the large uncertainity in how models resolve the meteorological features specific to urbanized areas and this has to be taken into account when designing different strategies for urban planning and multimodel approaches should be preferred.

How to cite: Huszár, P., Karlický, J., Ďoubalová, J., Nováková, T., Švábik, F., Belda, M., and Halenka, T.: Regional modeling of urban climate: the impact of physical process representation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7001,, 2020

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Presentation version 1 – uploaded on 01 May 2020
  • CC1: Comment on EGU2020-7001, Gaby Langendijk, 04 May 2020

    Hello Peter,

    1. Which Urban schemes were used in WRF / REGCM for the simulations you have analysed?
    2. How did your results compare with observations?
    3. Did it show the peak of the UHI at night or day time?
    4. Can you explain the difference between the UHI intensity between the two models? 

    Glad to discuss.

    The figures are a bit small, sorry if I missed something.

    • AC1: Reply to CC1, Peter Huszar, 04 May 2020

      Dear Gaby,

      thanks for the time dedicated to our poster:

      1. Which Urban schemes were used in WRF / REGCM for the simulations you have analysed?
      In WRF it was the mutlilayer BEP+BEM, singlelayer SLUCM and the BULK approach. In RegCM, we used the urban module of the CLM4.5 LSM. (see the table with different settings - use zoom please)
      2. How did your results compare with observations?
      We did a troughout comparison with urban measurements (not presented here) and found that models well reproduce the urban-rural contrast qualitatively but large differences exist between individual settings.
      3. Did it show the peak of the UHI at night or day time?
      Definitelly during night.
      4. Can you explain the difference between the UHI intensity between the two models? 
      This have probably multiple sources, but mainly the vertical transport of heat from the urban canopy  layer and the different landuse representation which is dominant in WRF and fractional in RegCM so the urban effects are, in general, stronger in WRF.

      if you would like to know any further information, do not hesitate to ask. 

      ps: for looking at details, please use zoom. The poster has a high dpi (data-per-inch), so all the detailes will appear if zoomed.

      • CC3: Reply to AC1, Gaby Langendijk, 04 May 2020

        Many thanks! Very clear answers.

  • CC2: Comment on EGU2020-7001, Steven C. Chan, 04 May 2020

    Do you by chance (if it is possible) to look at urban-rural contrast for precipitation?

    • AC2: Reply to CC2, Peter Huszar, 04 May 2020

      We did look at it, but could not include all the results in this poster due to space limits.
      We found statistically significant increases of summer convective precipiation, mainly for early evening hours.  

      • CC4: Reply to AC2, Steven C. Chan, 04 May 2020

        Thank you very much for the reply.

        Do you mean the increase of convective precipitation is for the urban areas?


        • AC3: Reply to CC4, Peter Huszar, 04 May 2020

          Yes, as a long term average and averaged over the whole urban and suburban areas.
          What I mean, that there is slightly more convective precipiation modelled by models for the areas of selected cities compared to their rural sourroundings. There were many cities included in the analysis so this results is considered as robust, at least for the region of interest ("larger" central Europe).