Validation of the PALM model system 6.0 in real urban environment; case study of Prague-Dejvice, Czech Republic

Abstract

Abstract. The PALM 6.0 model system has been rapidly developed in the recent years with respect to its capability to simulate physical processes within urban environments. In this regard, it includes e.g. energy-balance solvers for building and land surfaces, a radiative transfer model to account for multiple reflections and shading, as well as a plant-canopy model to consider the effects of plants on the (thermo)dynamics of the flow. This study provides a thorough evaluation of modelled meteorological, air chemistry and wall-surface quantities against dedicated in-situ measurements taken in an urban environment in Prague, Dejvice, Czech Republic. Measurements included e.g. monitoring of air quality and meteorology in street canyons, surface temperature scanning with infrared camera and monitoring of wall heat fluxes. Large-eddy simulations (LES) for multiple days within two summer and three winter episodes that are characterized by different atmospheric conditions were performed with the PALM model driven by boundary conditions obtained from a mesoscale model. For the simulated episodes, the resulting temperature, wind speed and concentrations of chemical compounds within street canyons agreed well with the observations, except the LES did not adequately capture nighttime cooling near the surface at certain meteorological conditions. In some situations, less turbulent mixing was modelled resulting in higher near-surface concentrations. At most of the surface evaluation points the simulated wall-surface temperature agreed fairly well with the observed one regarding its absolute value as well as daily amplitude. However, especially for the winter episodes and for modern buildings with multi-layer walls, the heat transfer through the wall is partly not well captured leading to discrepancies between the modelled and observed wall-surface temperature. Furthermore, we show that model results depend on the accuracy of the input data, particularly the temperatures of surfaces affected by nearby trees strongly depend on the spatial distribution of the leaf area density, land-surface temperatures at grass surfaces strongly depend on the initial soil moisture, or wall-surface temperatures depend on the correct prescription of wall material parameters, though these parameters are often not available with sufficient accuracy. Moreover, we also point out current model limitations, here we particularly focus on implications with respect to the discrete representation of topography on a Cartesian grid, complex heterogeneous facades, as well as glass facades that are not well represented in terms of radiative processes. With these findings presented, we aim to validate the representation of physical processes in PALM as well as to point out specific shortcomings. This will help to build a baseline for future developments of the model and for improvements of simulations of physical processes in an urban environment.

Geospatial input data for the PALM model system 6.0: model requirements, data sources and processing

“…In this study, the sensitivity of air and surface temperature, MRT, PET and PM10 within the PALM6.0 as a response to modification of basic surface material parameters as well as to common urbanistic strategies was evaluated. It was found that for this kind of simulations, the albedo and emissivity as well as thermal conductivity of walls and volumetric heat capacity of the materials play an important role (Belda et al, 2020). Figure 16.…”

“…Furthermore, a thorough validation of PALM in a real urban environment against in situ measurements is presented in Resler et al (2020). They especially focus on the representation of surface temperatures in PALM at different types of urban surfaces and also emphasize the need for accurate input data to be in agreement with in situ measurements.…”

High-Resolution Modelling of Thermal Exposure during a Hot Spell: A Case Study Using PALM-4U in Prague, Czech Republic

“…The simulations presented herein were performed for a domain in Prague-Dejvice, Czech Republic. At outset, they were validated against a study by [15].…”

Validation of the PALM model system 6.0 in a real urban environment: a case study in Dejvice, Prague, the Czech Republic

“…The model source code version 6.0 in revision r4508 used in this article is also available from https://doi.org/10.25835/0073713 (Resler et al, 2020a). The configurations and inputs of the model for all simulated episodes are available from http://hdl.handle.net/11104/0315416 (Resler et al, 2020b).…”