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

TLDR

The modelling of thermal exposure in outdoor urban environments is a highly topical challenge in modern climate research. This paper presents results from a new micrometeorological model that uses an integrated biometeorology module to model the Universal Thermal Climate Index (UTCI). The model, PALM‑4U, incorporates an integrated human body‑shape parameterization and was deployed for a pilot domain in Prague, Czech Republic. The simulations show that radiation drives spatiotemporal variability of thermal exposure, with highest exposure in street canyons on irradiated north sides of east–west streets and north–south streets, increased exposure near reflective buildings, and reduced exposure in tree‑shaded courtyards, where trees can lower UTCI by 4–9 °C and grass by 2–5 °C, illustrating PALM’s ability to reveal pedestrian‑level thermal exposure patterns for climate‑sensitive urban planning.

Abstract

The modelling of thermal exposure in outdoor urban environments is a highly topical challenge in modern climate research. This paper presents the results derived from a new micrometeorological model that employs an integrated biometeorology module to model Universal Thermal Climate Index (UTCI). This is PALM-4U, which includes an integrated human body-shape parameterization, deployed herein for a pilot domain in Prague, Czech Republic. The results highlight the key role of radiation in the spatiotemporal variability of thermal exposure in moderate-climate urban areas during summer days in terms of the way in which this directly affects thermal comfort through radiant temperature and indirectly through the complexity of turbulence in street canyons. The model simulations suggest that the highest thermal exposure may be expected within street canyons near the irradiated north sides of east–west streets and near streets oriented north–south. Heat exposure in streets increases in proximity to buildings with reflective paints. The lowest heat exposure during the day may be anticipated in tree-shaded courtyards. The cooling effect of trees may range from 4 °C to 9 °C in UTCI, and the cooling effect of grass in comparison with artificial paved surfaces in open public places may be from 2 °C to 5 °C UTCI. In general terms, this study illustrates that the PALM modelling system provides a new perspective on the spatiotemporal differentiation of thermal exposure at the pedestrian level; it may therefore contribute to more climate-sensitive urban planning.