Meteorologische Zeitschrift (Feb 2022)
Estimation of mean radiant temperature in cities using an urban parameterization and building energy model within a mesoscale atmospheric model
Abstract
During daylight hours, the mean radiant temperature Tmrt$T_{\text{mrt}}$ is one of the most important meteorological parameters to analyse heat stress for humans. This study conducts a spatio-temporal analysis of Tmrt$T_{\text{mrt}}$ for a summer period in 2018 for the city of Berlin, Germany. To this end, the mesoscale climate model COSMO-CLM (CCLM) is coupled with the urban Double Canyon Effect Parameterization scheme with a building energy model (DCEP–BEM) to derive Tmrt$T_{\text{mrt}}$. This coupled model system CCLM/DCEP–BEM enables a dynamic calculation of Tmrt$T_{\text{mrt}}$ for the microscale urban street canyons using a mesoscale model. To bring a more accurate comparison, a two-step approach is applied to assess the radiative fluxes and Tmrt$T_{\text{mrt}}$ from CCLM/DCEP–BEM. The radiation model SOLWEIG is first validated against measurement and then used to evaluate the DCEP–BEM model. Overall good agreement in Tmrt$T_{\text{mrt}}$ is found between CCLM/DCEP–BEM and SOLWEIG (R2=0.96$\text{R}^2 =\nobreak 0.96$). Nighttime Tmrt$T_{\text{mrt}}$ simulated with CCLM/DCEP–BEM is higher than that with SOLWEIG (MBE=2.9K$\text{MBE}=\nobreak 2.9\,\text{K}$), yet closer to measurements. Tmrt$T_{\text{mrt}}$ during the afternoon hours modeled with CCLM/DCEP–BEM is underestimated compared to SOLWEIG (MBE=-3.1K$\text{MBE}=\nobreak -3.1\,\text{K}$). Further, excluding vegetation, higher values for nighttime Tmrt$T_{\text{mrt}}$ are found in the densely built-up city center than in the suburbs with more open structures, while the city center has lower values for Tmrt$T_{\text{mrt}}$ during midday. This study provides a reliable representation of Tmrt$T_{\text{mrt}}$ in a mesoscale model and would be beneficial for future implementation of human-biometeorological variables such as the Universal Thermal Climate Index or Physiological Equivalent Temperature. These quantities are calculated using Tmrt$T_{\text{mrt}}$.
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