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

Modelling the Efficiency of Nature-Based Solutions to Decrease Extreme Summer-time Heat in Dense Urban Environment on Example of Vienna, Austria

Densely built urban environments experience extremely high temperatures during summer heat waves. Nature-based Solutions (NbS), such as increasing green infrastructure by replacing sealed surfaces with vegetation, installing green roofs and especially planting trees can ameliorate severe heat conditions by providing cooling through evapotranspiration and shading. This study analyses the effectiveness of NbS to reduce the summer maximum temperatures in Vienna using an urban climate modelling approach that takes into account NbS performance criteria on micro-scale and upscales the application of NbS for the entire city. Using existing data of the Viennese urban structure, status-quo urban climate simulations were performed. Further, based on evidence on NbS performance criteria different climate scenarios for implementation of NbS were designed. A densely-built area in Vienna, for which the possibility of implementation of NbS was analysed, was chosen as a study area for micro-scale simulations. The adaptation measures included: 1) reduction of soil sealing, 2) increase in surface reflectivity of sealed surfaces, 3) implementation of green roofs, 4) new park areas with trees and low vegetation and 5) a combination of all NbS. The modelling simulations were performed for a representative clear-sky heat day for NbS scenario first for the selected area with the ENVI-met model and later for the entire city of Vienna with the MUKLIMO_3 model. The extent of NbS was proportionally scaled for the city-level simulations and the measures were applied for all densely-built areas in the city. The results show the highest cooling effect for the combination of NbS with a similar intensity of cooling found both in microscale and city-scale simulations. In case of city-scale simulations, the results show mean difference in daily maximum temperature of about 0.1°C and maximum difference of about 1.4°C. The effect is strongest in the densely-built areas where the measures were applied. However, the cooling effect can be detected in the surrounding areas as well. The robustness of the urban scale results was tested using different modelling setups, varying the parameters describing land-use properties, such as variations in land use mapping, soil sealing, building density and tree coverage. Different representation of land use characteristics in the model leads to variations in spatial pattern of heat load. The cooling effect also varies spatially, dependent on the possibility to implement the adaptation measure. However, the results confirm similar efficiency of NbS regardless of the background data and method applied

Using urban climate modelling and improved land use classifications to support climate change adaptation in urban environments: A case study for the city of Klagenfurt, Austria

This study outlines the results of current and future climate scenarios, and potentially realizable climate adaptation measures, for the city of Klagenfurt, Austria. For this purpose, we used the microscale urban climate model (MUKLIMO_3), in conjunction with the cuboid method, to calculate climate indices such as the average number of summer and hot days per year. For the baseline simulation, we used meteorological measurements from 1981 to 2010 from the weather station located at Klagenfurt Airport. Individual building structures and canopy cover from several land monitoring services were used to derive accurate properties for land use classes in the study domain. To characterize the effectiveness of climate adaptation strategies, we compared changes in the climate indices for several (future) climate adaptation scenarios to the reference simulation. Specifically, we considered two major adaptation pathways: (i) an increase in the albedo values of sealed areas (i.e., roofs, walls and streets) and (ii) an increase in green surfaces (i.e., lawns on streets and at roof level) and high vegetated areas (i.e., trees). The results indicate that some climate adaptation measures show higher potential in mitigating hot days than others, varying between reductions of 2.3 to 11.0%. An overall combination of adaptation measures leads to a maximum reduction of up to 44.0%, indicating a clear potential for reduction/mitigation of urban heat loads. Furthermore, the results for the future scenarios reveal the possibility to remain at the current level of urban heat load during the daytime over the next three decades for the overall combination of measures

Urban Heat Island Hazard and Risk Indices for Austria

This collection contains two geotiffs: the UHI Hazard Index and the UHI Risk Index, both for Austria at a 100 m resolution. The methodology for their development is described in the attached factsheets (in English and German)

Urban climate in central european cities and global climate change

Urban areas are among those most endangered with the potential global climate changes. The studies concerning the impact of global changes on local climate of cities are of a high significance for the urban inhabitants' health and wellbeing. This paper is the final report of a project (Urban climate in Central European cities and global climate change) with the aim to raise the public awareness on those issues in five Central European cities: Szeged (Hungary), Brno (Czech Republic), Bratislava (Slovakia), Kraków (Poland) and Vienna (Austria). Within the project, complex data concerning local geomorphological features, land use and long-term climatological data were used to perform the climate modelling analyses using the model MUKLIMO_3 provided by the German Weather Service (DWD)

Supporting Climate Adaptation Measures in Small- to Medium-Sized Austrian Cities Using Climate Modelling

This study outlines the results of current climate conditions for the city of Mödling, Klagenfurt and Salzburg located in Austria. Furthermore, it will analyse specific measures regarding climate adaptation, which are potentially realizable. To characterize the current climate conditions with the average number of summer days per year (SD y−1), we use the microscale urban climate model MUKLIMO_3, in combination with a trilinear interpolation method. For the reference model simulation, we use atmospheric observations from 1981 to 2010 provided by one weather station located in a rural site near each city. We combined different land use data sets with various spatial resolutions to evaluate precise properties for the land use classification. Furthermore, we compared changes in SD y−1 to the reference simulation to evaluate the effectiveness of the here proposed adaptation strategies. Specifically, we consider two types of adaptation measures: (i) an increase in the shortwave reflectivity of impervious and sealed areas and (ii) an increased number of low-vegetated areas (i.e. lawns on streets and at roof level) and high-vegetated areas (i.e. bushes and trees). The results of the individual simulations indicate a substantially decreased SD y−1 by up to − 7.3 (− 10.9%) for the case of highly reflective roofs and up to − 7.7 (− 22.7%) for the case of an increased number of trees. A combination of both pathways leads to a decrease in SD y−1 by up to − 19.4 (− 29.3%), indicating a clear potential to mitigate the heat burden in each city

Supporting climate proof planning with CLARITY's climate service and modelling of climate adaptation strategies – the Linz use-case

In recent years, the representation of climate information in a way to support decision making has been gaining momentum. Worldwide, these so-called climate services are emerging as an essential tool to connect the advances in climate science with the domains of climate change adaptation. The methodology developed within the CLARITY project (funded through European Union funding program Horizon 2020) is aimed at implementing a new generation of climate services specifically designed to assess adaptation measures at the city level under the effects of extreme weather events in the context of climate change. These effects are assessed based on observations as well as climate projections, and the subsequent derivation of climate indices to address changes in climate extremes. The dynamical-statistical downscaling of regional climate model results is used to obtain this information on fine spatial scales (100 m), hence providing urban scale projections and enabling climate sensitivity simulations of adaptation measures on the urban scale. The climate adaptation strategies encompass, among others, green roofs, increasing roof albedo, as well as changes in soil sealing. Here, the climate assessment methodology developed within CLARITY will be discussed in detail, and results for the city of Linz (Austria) presented. In addition, the usage of these methods and results within the CLARITY climate service as well as the connection to urban climate change resilience will be highlighted