| 1. |
- Bäcklin, Oskar, 1991, et al.
(författare)
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Outdoor heat stress at preschools during an extreme summer in Gothenburg, Sweden - Preschool teachers’ experiences contextualized by radiation modelling
- 2021
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Ingår i: Sustainable Cities and Society. - : Elsevier BV. - 2210-6707. ; 75
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Bäcklin, Oskar, 1991, et al.
(författare)
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Outdoor heat stress at preschools during an extreme summer in Gothenburg, Sweden - Preschool teachers’ experiences contextualized by radiation modelling
- 2022
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Ingår i: Multiple Nordic Geographies 9th Nordic Geographers Meeting 19th - 22nd of June 2022 Joensuu, Finland.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- With increasing urbanisation and climate change, heat stress issues are becoming increasingly important to consider in order to create sustainable urban environments worldwide. Heat affects all groups in society, although small children are especially vulnerable due to physiological factors as well as limitations in their everyday mobility. Therefore, it is crucial to ensure that outdoor areas used by children, such as preschools provide healthy safe thermal conditions. Trees are proven effective heat mitigating objects, as well as highly appreciated features of preschool yards for their aesthetic and pedagogical aspects. However, there is a large variation in the amount of trees at preschool yards which can prove to be problematic regarding thermal comfort and well-being for both children and preschool teachers today and in the future. Using a mixed-method approach consisting of 19 interviews with preschool teachers, and modelling outdoor thermal conditions on 440 preschool yards, the occurrence of heat stress in Gothenburg preschools during the heat wave of 2018 and its effects on preschools has been studied. One third of modelled preschool yards were found to have more than 50% of the preschool yard area exposed to strong heat stress during a warm and sunny summer days, implying children in many preschools have significantly less play area than current guidelines deem sufficient. Shading, which was found mainly provided by trees within preschool yards rather than from objects in surrounding areas, provide effective heat mitigation. Shading devices such as shade-sails were found prone to breakage and not providing sufficient shading. Thus, shading devices are not suggested as a long-term solution for heat mitigation at preschool yards. Interviews confirmed that excessive heat conditions at preschool yards cause tired, drowsy and overheated children as well as forcing the preschool to prioritise care over pedagogical activities. The results demonstrated that heat stress is a problem at many Gothenburg preschools, with difficulties in ensuring the well-being of children at many preschools as a consequence. The strong correlation found between amount of trees at preschool yards and less heat stress highlight the importance of trees for heat mitigation.
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| 3. |
- Wallenberg, Nils, 1986, et al.
(författare)
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9B.8: The Influence of Anisotropic Diffuse Radiation on Mean Radiant Temperature in Outdoor Urban Environments
- 2018
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Ingår i: 10th International Conference on Urban Climate/14th Symposium on the Urban Environment, New York, US, August 2018.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- One of the most important meteorological variables when estimating outdoor thermal comfort is the mean radiant temperature (Tmrt). Tmrt is estimated from the flux of short-wave and long-wave radiation between a human and its surroundings. During clear weather conditions the main part of the short-wave irradiance originates from Sun direct-beam radiation. However, part of the short-wave radiation is also originating from all-sky diffuse radiation. As of now most models for radiant load simulations considers the sky to be isotropic when estimating diffuse radiation. This leads to misinterpretations of the diffuse radiation, especially close to walls where the sky-view factor controls the amount of radiation that reaches the ground. Here we use the SOLWEIG model to examine the effects of an anisotropic diffuse model (Perez et al. in 1993) on short wave radiant loads as well as Tmrt for pedestrians in outdoor urban environment. Comparisons between the anisotropic model and the isotropic model indicates that the diffuse radiation in the isotropic model is overestimated in areas in front of north facing walls and underestimated in areas in front of south facing areas. These deviations, in turn, have implications for the Tmrt. The deviations in diffuse radiation thus signifies the importance of using an anisotropic model when estimating diffuse radiation and Tmrt, especially in densely built areas where the sky-view factor controls large parts of the radiation that reaches the ground.
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| 4. |
- Wallenberg, Nils, 1986, et al.
(författare)
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An anisotropic parameterization scheme for longwave irradiance and its impact on radiant load in urban outdoor settings
- 2023
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Ingår i: International Journal of Biometeorology. - : Springer Science and Business Media LLC. - 0020-7128 .- 1432-1254. ; 67, s. 633-47
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Tidskriftsartikel (refereegranskat)abstract
- 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 R2 and RMSE for Tmrt of 0.94 and 4.6 °C, respectively, and R2 and RMSE for longwave radiation of 0.89 and 14.1 Wm−2, respectively. Simulations show that mean radiant temperature (Tmrt) 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 Tmrt with the new parameterization and old parameterization schemes, previously overestimated Tmrt 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, Tmrt 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 Tmrt of humans in outdoor settings.
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| 5. |
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| 6. |
- Wallenberg, Nils, 1986, et al.
(författare)
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Locating trees to mitigate outdoor radiant load of humans in urban areas using a metaheuristic hill-climbing algorithm – introducing TreePlanter v1.0
- 2022
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Ingår i: Geoscientific Model Development. - : Copernicus GmbH. - 1991-959X .- 1991-9603. ; 15:3, s. 1107-1128
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Wallenberg, Nils, 1986
(författare)
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Outdoor heat in urban areas - Model development and applications
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Heat waves and high outdoor air temperature can lead to heat stress with negative implications for human health and wellbeing such as heat stroke, heat cramps, dehydration and in extreme cases death. The urban population is at higher risk of such outcomes because of the generally warmer urban climate. Daytime outdoor thermal comfort is substantially affected by short- (solar) and longwave (thermal) radiation, i.e. mean radiant temperature (Tmrt). The aim of this thesis is to deepen the knowledge of radiant conditions in complex urban areas and how such knowledge can be utilized in modelling of Tmrt and thermal comfort of humans. The overall aim is examined in three parts. The first part examines the effects of anisotropic (non-uniform) estimations of sky diffuse shortwave radiation and longwave radiation in the SOlar and LongWave Environmental Irradiance Geometry model (SOLWEIG) and how these influences Tmrt of humans in outdoor urban environments, compared to isotropic conditions. The results show that anisotropic sky diffuse shortwave radiation and longwave radiation are important in estimations of Tmrt. The circumsolar and horizon regions irradiates more diffuse shortwave radiation when the sky is anisotropic, which increases radiant load mainly in sunlit areas. Anisotropic sky longwave radiation increases with zenith angle, reaching its maximum at the horizon, resulting in higher Tmrt in open areas where the horizon region is visible. The second part focuses on outdoor thermal comfort of preschoolers in Sweden in the present and future climate using SOLWEIG. It is concluded that two thirds of preschool yards in Gothenburg have 50% or more of their yard area exposed to strong heat stress. Heat stress in preschools lead to drowsy, tired and overheated children, with negative consequences for the pedagogical activities, forcing teachers to ensure that children stay cool on the expense of education. Heat stress days are expected to increase in the future, potentially exacerbating already existing heat related issues. However, with abundant tree shade heat stress is limited, both in the present and in the future. In the third part optimized locations for trees to mitigate excessive Tmrt with regards to the shading effect of trees is analyzed. Tree positions depend on tree size and what time of day when shading is required. The results of this thesis highlights the significance of realistic models, importance of applied studies to identify heat related problems and how such problems can be mitigated.
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| 8. |
- Wallenberg, Nils, 1986, et al.
(författare)
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Present and future heat stress of preschoolers in five Swedish cities
- 2023
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Ingår i: Climate Risk Management. - 2212-0963. ; 40
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Wallenberg, Nils, 1986, et al.
(författare)
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The effects of warm weather on children’s outdoor heat stress and physical activity in a preschool yard in Gothenburg, Sweden
- 2023
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Ingår i: International Journal of Biometeorology. - 0020-7128 .- 1432-1254. ; 67:12, s. 1927-40
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Wallenberg, Nils, 1986, et al.
(författare)
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The influence of anisotropic diffuse shortwave radiation on mean radiant temperature in outdoor urban environments
- 2020
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Ingår i: Urban Climate. - : Elsevier BV. - 2212-0955. ; 31
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Tidskriftsartikel (refereegranskat)abstract
- 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 (Tmrt), 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 Tmrt, which can differ by up to 3 °C. The deviations in D thus signify the importance of using an anisotropic model when estimating D and Tmrt, 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.
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