Evaluation of High-Resolution Simulation of the Urban Heat Island in Vienna, Austria

The recently developed microscale model for urban applications PALM-4U was used to simulate the thermal variability in Vienna on different spatial scales and to evaluate its ability to capture thermal characteristics in real urban environment. The model simulations cover the entire city of Vienna with a spatial resolution of 20 m. The static data related to geographical information and urban infrastructure are based on GIS data provided by the city administration of Vienna, available as spatial multi-purpose maps (Flächen-Mehrzweckkarte - FMZK), street tree cadastre, Digital Elevation Model and Digital Surface Model, which were combined with the national land cover data (Land Information System Austria - LISA) to account for the unresolved vegetation and Open Street Map to include building properties in the surrounding region (Lower Austria) of the model domain. The simulations were performed for a selected clear-sky hot day in August 2022. The results for hourly air temperature were evaluated with conventional weather stations of the national weather service and the city of Vienna and with quality-controlled data from citizen weather stations from the company NETATMO. The results show high intra-urban variability during daytime, but distinct spatial patterns at night with higher air temperatures in urban regions. In addition, spatial patterns of surface temperature were compared to remote sensing data from ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) and with the modelling results from previous studies, but with coarser grid spacing (e.g. urban climate model MUKLIMO_3 with 100 m spatial resolution). The results indicate that the microscale model PALM-4U shows general agreement with observations and is able to simulate atmospheric processes in urban regions. However, during the night a strong temperature inversion is present in the model, which can be related to the choice of model configuration and requires further investigations. The spatial patterns in urban-rural temperature gradient are similar as found in coarser scale model simulations and remote-sensing data, but show higher variation in surface temperature amplitude