The Air-temperature Response to Green/blue-infrastructure Evaluation Tool (TARGET) is a compact urban climate model designed to predict intra-urban temperatures and assess city cooling strategies. Until now, the lack of a user interface has limited its broader adoption. This study presents an open-source interface for TARGET, integrated within the Urban Multi-scale Environmental Predictor (UMEP) tool in QGIS. The interface supports a complete workflow, including input data preparation, simulation, and output visualisation. Its applicability is demonstrated through a case study in Zurich, Switzerland, where it identified thermal hotspots and quantified the cooling benefits of targeted interventions. By lowering technical barriers, UMEP-TARGET enhances the accessibility of physically based urban temperature modelling for both the scientific community and practitioners, supporting evidence-based planning for climate adaptation.

The urban climate is highly influenced by its building geometry, material characteristics, street orientation and high fraction of impermeable surfaces. All of these influence the microclimate and the resulting outdoor thermal comfort. Mean radiant temperature (Tmrt) is often used as an estimator for heat exposure as it is one of the most important variables governing outdoor human thermal comfort on clear, calm and warm days. The highest values of Tmrt are commonly found in front of sunlit facades where a human is exposed to high levels of direct and reflected shortwave radiation from the sun, as well as high levels of longwave radiation emitted from surrounding sunlit walls. As a consequence, outdoor thermal comfort modelling requires accurate simulation of wall surface temperatures (Ts).The aim of this study is to present a step heating approach for calculating wall Ts in the SOlar and LongWave Environmental Irradiance Geometry model (SOLWEIG) and quantify how it influences Tmrt. This method requires information on material characteristics, i.e. specific heat capacity, density, thermal conductivity, albedo and thickness of the outer layer of the wall, as well as radiation balance at the wall surface, and ambient air temperature. Simulated Ts is compared to observed Ts of two white walls (albedo = 0.5) in Gothenburg, Sweden; one wooden wall and one plaster brick wall. The simulations show high agreement with the 15 394 observations, with R2=0.93 and RMSE = 2.09 degrees C for the wooden wall and R2=0.94 and RMSE = 1.94 degrees C for the plaster brick wall. For the walls presented here, this new parameterization scheme results in differences in Tmrt of up to 2.5 degrees C compared to the previous version of SOLWEIG.With this new approach, SOLWEIG can be used to evaluate the effect of building materials on outdoor thermal comfort. The speed and accuracy of this approach suggests that it also could be applied in other areas where Ts of walls are important, for example building energy models and urban energy balance models.

Street trees are important climate adaptation tools to combat urban overheating, an issue that an increasing number of cities face. To address this, the high-resolution microclimate model SOLWEIG is a valuable tool to simulate Mean Radiant Temperature (Tmrt) exposure for pedestrians. In this parametric study, we quantify how urban street trees reduce outdoor radiant heat exposure across a range of street canyon aspect ratios. We introduce the Radiative Cooling Efficiency (RCE) metric, which normalizes the Tmrt reduction by relative canopy cover, to standardize the comparisons of tree-induced reductions in Tmrt across urban morphologies. This workflow is applied to the city of Ghent, Belgium, of which we collected a dataset of street canyon geometries (building height, canyon width, street orientation) and urban tree characteristics (canopy height, trunk height, shortwave transmissivity). Within these representative parameter ranges, simulations of Tmrt were performed at a 1-meter resolution under clear-sky conditions on the hottest day of 2024 in Belgium. The results show that canyon width and orientation dominated the tree’s cooling efficiency: trees in east-west canyons had up to 2.8 times higher impact than those in north-south canyons. Regarding tree modeling parameters, a sensitivity analysis revealed that lowering the trunk height had 2.3 times the effect of increasing canopy height. In addition, each 1% rise in tree shortwave transmissivity reduced cooling by approximately 1.4%. These findings highlight the interactions between the urban morphology and vegetation structure in modeling pedestrian thermal comfort and are relevant for both modelers and urban planners.

In an era of changing climate, rapid urbanization, and densification there is a need for spaces that can manage extreme weather events, such as heat waves and heavy precipitation, whilst simultaneously be attractive for the urban citizens, i.e., multifunctional spaces. In this paper a framework for integrated assessment of the potential of multiple urban blue-green infrastructure (BGI) elements to provide climate regulating and social functions, i.e. multifunctionality potential, based on best research available, in relation to cost for construction and maintenance to be used in planning is presented. The assessment of functions and costs is done on a nominal scale from 1 to 5 using a mixed-method approach (systematic literature review, model simulations and workshops). The integrated assessment is presented in a multifunctionality potential and cost matrix and allows for weighting of each function and cost, as their relative importance is context dependent. It is shown that the majority of BGI elements have a relatively low potential to provide multifunctionality in terms of urban stormwater management, heat stress reduction and recreation. Some of them to a low cost (e.g., road verges, ditches, permeable pavements) others to a high cost (e.g., green roofs and walls). The highest multifunctionality potential is found in large parks, but to a high cost. The most favourable element, i.e., high potential in relation to costs is urban forests. The matrix presented here is considered usable for making general well informed integrated decisions in planning and to enhance the awareness of single and multiple functions of BGI elements.

Swedish buildings are well insulated for winter climate, but often not optimized for summer, leading to risks of overheating during heat extremes (including heat waves). Along with a warmer climate, the risks of overheating and need for cooling are expected to increase.In this study, present and future intensity, frequency and length of overheating, based on the newly implemented recommendations for indoor temperature from the Swedish Public Health Agency, is assessed for a typical Swedish multi-story residential building in Gothenburg, Sweden. Overheating is simulated for different floor levels and room orientations using the IDA-ICE building performance simulation software. The present climate (2008–2020) is represented by observed meteorological data and the future climate (2071–2100) by statistically downscaling the observations based on RCP4.5 simulations from the EURO-CORDEX project. Furthermore, the shading effect of trees at varying distances from the building is explored.Results show that overheating occurs during heat extremes from April to October, with the highest frequency in July. Overheating periods are projected to become more intense, more frequent and longer by the end of the century. During heat waves, overheating occurs throughout the day and may last for weeks, potentially impacting not only risk groups but also the general population. The risk of overheating increases with floor level and is largest for rooms facing west and south with large windows. Trees close to buildings considerably reduce overheating in the present as well as in the future warmer climate, highlighting their effective passive cooling potential during heat extremes.The results, which are considered applicable to a large part of the building stock in Sweden as well as in other countries with similar climate and building practices, highlight the present and future challenges with overheating and the potential of trees for mitigating overheating and reducing the cooling demand in buildings.

Urban citizens are particularly exposed to heat stress during heatwaves due to the urban climate conditions. Introducing more trees, changing building density and surface cover and materials are examples of planning measures that can be used to mitigate heat stress. One challenge as an urban planner is to have knowledge on which mitigation measure to implement to achieve the highest cooling effect with regards to outdoor heat stress at different spatial scales. The aim of this high-resolution modelling of outdoor thermal comfort on city-wide domains is to examine how different real-world urban settings reduce or exacerbate heat stress with regards to building density (plan area index), tree fraction, and ground cover. Here, we exploit the open-source tool Urban Multi-scale Environmental Predictor (UMEP), to investigate how real-world data on building density, tree fraction, and ground cover influence thermal comfort in the three largest cities in Sweden. Mean radiant temperature (Tmrt) and two thermal comfort indices are calculated and compared: Physiological Equivalent Temperature (PET) and Universal Thermal Comfort Index (UTCI). Automated chain processes using Python scripting is demonstrated, making it possible to derive microscale outdoor thermal comfort information (2-meter resolution) using a standard personal computer and open data sources. Results show that tree fraction is the single most effective outdoor heat mitigation measure, especially in areas with low building density. Results also show that building fraction has a minor cooling effect. This is probably due to the fact that shadowing at street level is dominated by trees due their 3D characteristics including trunk zones. Tmrt shows very similar results compared with PET and UTCI, indicating that Tmrt can capture the spatial variations of heat stress during warm, clear and calm days. Since trees is the single most effective measure to mitigate heat stress, it should be incorporated when creating practical guidelines to resilient urban planning strategies against heat stress.

Heat stress can have negative effects on human wellbeing with morbidity and mortality as harmful consequences, especially in vulnerable groups, e.g. children, elderly and chronically ill. Children is for example at higher risk of dehydration and heat stroke compared to healthy adults. Furthermore, children attending preschools are endorsed to spend time outdoors and engaging in physical activities. Therefore, thermally comfortable preschool yards are detrimental to sustain safe environments where the children can continue their physically active play. Here we show that preschoolers in five Swedish cities, Malmö, Gothenburg, Stockholm, Östersund and Luleå, are exposed to heat stress on warm and clear days between May-August in preschool yards with insufficient shading, using three different thermal indices (COMFA, PET and UTCI). Furthermore, future number of heat stress days are evaluated using the SMHI RCA4 regional climate model from the EURO-CORDEX project, forced with six different global climate models. Results show that heat stress will increase under the RCP2.6, 4.5 and 8.5 climate change scenarios. In Malmö, Gothenburg and Stockholm number of days with heat stress all hours 09:00–15:00 while playing in a sunlit sandbox have doubled from approximately 10 to 20 days for 2071–2100 (RCP8.5) compared to 2008–2020. These numbers are even higher if active play, e.g. running, is performed, estimating to around two weeks in July alone by the end of the century. Without adaptation this is likely to have adverse effects on the health and learning of children. If the preschool yard, on the other hand, is shaded by trees, days with heat stress are almost entirely diminished, indicating the importance of trees in preschool yard design as a tool to mitigate heat stress.

Warm weather can have negative effects on the health and wellbeing of humans, especially risk groups e.g. children. Methods for estimating thermal comfort and physiological stress outdoors are not developed or adjusted for children. A consequence of this is few existing studies on children and thermal comfort and heat stress, particularly in a Swedish context. Children are at higher risk of heat stress than adults because of a larger body-surface-area to body-mass-ratio, lower sweat rate and that they are less aware of their thermal status. Swedish children attending preschool spend around three hours per day outdoors and the effects of weather and outdoor environment design on children’s thermal comfort are not clear. By better understanding how weather affects children's thermal comfort, measures can be taken to reduce heat stress and increase children's health and wellbeing. Here we present results from a project on the effect of warm weather on Swedish preschooler’s health and wellbeing. The results are based on detailed observations and simulations for present day climate as well as future climate change scenarios and give indications on exposure to heat stress and potential implications on the health and wellbeing of the children. For example, two thirds of preschool yards in Gothenburg are exposed to strong heat stress on clear and warm days. Strong heat stress have negative consequences for the pedagogic activities and wellbeing. Moreover, days with strong heat stress will increase in the future in exposed yards, whereas yards with sufficient shade are less prone to heat stress.

The Urban Multi-scale Environmental Predictor (UMEP) is a city based climate service tool that facilitate user-friendly open source capabilities to combine models and tools essential for climate simulations. The tool is designed for a broad range of users, both within academia as well as practitioners and non-expert users. UMEP is available as a plugin in QGIS, a free and open source geographic information system (GIS) available on all common platforms. One main purpose with UMEP is to include pre-processing of geo- and weather data, process calculations as well as post-processing and visualisation in the same tool.Recent developments in UMEP enables creation of all essential input variables required to generate high-resolution raster grid of common human thermal comfort indices such as Physiological Equivalent Temperate (PET), Universal Thermal Comfort Index (UTCI), Comfort Formula (COMFA) etc. This work presents initial results and methodology used to compute these indices within UMEP. Examples of workflow throughout the process, all the way to the final result, will be presented and discussed.

A robust representation of the radiative properties in complex urban settings is important for accurate estimations of radiant load. Here, we present a new parameterization scheme in the SOlar and LongWave Environmental Irradiance Geometry (SOLWEIG) model that partitions the upper hemisphere into 153 patches. Partitioning of the upper hemisphere enables determination if longwave irradiance originates from the sky, vegetation, sunlit building surfaces, or shaded building surfaces from each patch. Furthermore, a model for anisotropic sky longwave irradiance where emissivity increases with zenith angle is included. Comparisons between observations and simulations show high correlation, with R 2 and RMSE for T mrt of 0.94 and 4.6 °C, respectively, and R 2 and RMSE for longwave radiation of 0.89 and 14.1 Wm −2 , respectively. Simulations show that mean radiant temperature ( T mrt ) can be up to 1.5 °C higher with an anisotropic sky compared to a uniform sky as an effect of higher radiant load on the vertical of a human when sky longwave irradiance increases with zenith angle. In comparisons of simulated T mrt with the new parameterization and old parameterization schemes, previously overestimated T mrt under trees (high sky obstruction, sky view factor (SVF) < 0.3) can be decreased by up to 3 °C from more realistic estimations using the patches. Moreover, T mrt close to sunlit walls (SVF ~ 0.5) is increased by up to 2–3 °C from increased exposure to sunlit surfaces. Concluding, anisotropic sky longwave radiation and directionality of longwave radiation from different sources are important in estimations of T mrt of humans in outdoor settings.

Hot weather conditions can have negative impacts on the thermal comfort and physical activity of vulnerable groups such as children. The aim of this study is to analyze the effects of warm weather on 5-year-old children's thermal comfort and physical activity in a preschool yard in Gothenburg, Sweden. In situ measurements were conducted for 1-1.5 h in the early afternoon on 8 days in May, June, and August of 2022. The thermal comfort and physical activity was estimated with GPS-tracks, heart rate monitors, and step counts and compared to observed weather conditions. Results show that physical activity decreases under warmer weather conditions, depicted by a decrease in distance moved, step counts, and highest registered pulse. Moreover, on warm days, the children avoid sunlit areas. For 50% or more of the time spent in sunlit areas, the children are exposed to cautious levels of heat. In shaded areas, on the other hand, the children are less exposed, with five out of 8 days having 50% or more of the time at neutral levels. The study demonstrates the importance of access to shaded areas in preschool yards where children can continue their active play while simultaneously maintaining a safe thermal status.

Mean radiant temperature (Tmrt) is a frequently used measure of outdoor radiant heat conditions. Excessive Tmrt, linked especially to clear and warm days, has a negative effect on human wellbeing. The highest Tmrt on such days is found in sunlit areas, whereas shaded areas have significantly lower values. One way of alleviating high Tmrt is by planting trees to provide shade in exposed areas. Achieving the most efficient mitigation of excessive Tmrt by tree shade with multiple trees requires optimized positioning of the trees, which is a computationally extensive procedure. By utilizing metaheuristics, the number of calculations can be reduced. Here, we present TreePlanter v1.0, which applies a metaheuristic hill-climbing algorithm on input raster data of Tmrt and shadow patterns to position trees in complex urban areas. The hill-climbing algorithm enables dynamic exploration of the input data to position trees, compared with very computationally demanding brute-force calculations. The hill-climbing algorithm has been evaluated with a static greedy algorithm that positions trees one at a time based on ranking and is expected to always find relevant locations for trees. The results show that the hill-climbing algorithm, in relatively low model runtime, can find positions for several trees simultaneously, which lowers Tmrt substantially. TreePlanter, with its two algorithms, can assist in optimization of tree planting in urban areas to decrease thermal discomfort.

Using a mixed-method approach consisting of interviews with preschool teachers and modelling of the outdoor thermal conditions using the mean radiant temperature as an indicator of heat stress, the occurrence of heat stress in Gothenburg preschools during the summer of 2018 and its effects have been studied. One third of 440 preschool yards modelled have more than 50% of the preschool yard-area exposed to strong heat stress during a warm and sunny summer day, implying children in many preschools have considerably less play area than current guidelines deem sufficient. Shade, where present, was mostly from trees within the preschool yards themselves rather from objects in surrounding areas, provided effective heat mitigation. Interviews confirmed that excessive heat conditions at preschool yards resulted in tired, drowsy and overheated children as well as forcing the preschool to prioritise care over pedagogical activities. The results demonstrated that heat stress occurs at Gothenburg preschools, with difficulties in ensuring the well-being of children at many preschools as a consequence. Many preschools need more shade, preferably from trees to provide healthy and secure environments for preschool children. Finally, the study highlights the need for more research on how weather and outdoor environments affect children's activity and well-being.

Test dataset for TreePlanter v1.0 (http://doi.org/10.5281/zenodo.4616761). The geodata originates from the Building and Planning Office in Gothenburg, Sweden. Meteorological data is from the Swedish Meteorological and Hydrological Institutes weather station number 92513 (WMO 2513).

During clear weather conditions the main part of the shortwave irradiance derives from sun direct-beam radiation. However, part of the shortwave radiation also originates from all-sky diffuse radiation (D), with a large part being circumsolar in origin. Many radiation models considers the sky as isotropic when estimating D. Here we implement an anisotropic model for D into the SOLWEIG model to examine the spatial patterns of D in a built-up environment, as well as its influence on mean radiant temperature (T-mrt), a variable essential for estimating outdoor human thermal comfort. Comparisons between the anisotropic and the isotropic models indicates that the D in the isotropic model is overestimated in shaded areas and underestimated in areas close to sunlit walls. This is explained by the circumsolar origin of D during clear and semi-cloudy conditions and solar altitude. These over- and underestimations, consecutively, have implications for T-mrt, which can differ by up to 3 degrees C. The deviations in D thus signify the importance of using an anisotropic model when estimating D and T-mrt, especially since the areas with the highest reported radiant loads receive even more radiation considering an anisotropic diffuse sky, i.e. the hottest areas are even hotter than previously reported.