•We review the methodological approach of 26 studies on outdoor thermal comfort.•The methodology used is often poorly described and reporting is insufficient.•Inconsistencies in the determination of ...the mean radiant temperature and wind speed.•Subjective judgement scales regarding thermal perception often do not match.•There is a need for standardization and guidance of outdoor thermal comfort studies.
In this paper we review instruments and methods used to assess outdoor thermal comfort and subjective thermal perception in 26 studies reported in the literature during the last decade, covering a wide range of climates and geographical contexts. We found a great variety of instruments and methods used to measure meteorological variables, especially with respect to the mean radiant temperature and wind speed. Moreover, many different subjective judgement scales were used to assess subjective thermal perception, thermal neutrality and thermal preference and a multitude of thermal indices were used to quantify the combined effect of meteorological variables on thermal perception. The use of a variety of methods makes it difficult to compare results of the different studies. There is thus a need for standardization and to give guidance regarding how to conduct field surveys in outdoor environments. Such standards and guidelines should give advice regarding the choice of measurement sites, type and positioning of instruments, appropriate methods to determine the mean radiant temperature, questionnaire design and suitable thermal comfort indices. These guidelines should also include advice on reporting.
Due to the complexity of built environment, urban design patterns considerably affect the microclimate and outdoor thermal comfort in a given urban morphology. Variables such as building heights and ...orientations, spaces between buildings, plot coverage alter solar access, wind speed and direction at street level. To improve microclimate and comfort conditions urban design elements including vegetation and shading devices can be used. In warm-humid Dar es Salaam, the climate consideration in urban design has received little attention although the urban planning authorities try to develop the quality of planning and design. The main aim of this study is to investigate the relationship between urban design, urban microclimate, and outdoor comfort in four built-up areas with different morphologies including low-, medium-, and high-rise buildings. The study mainly concentrates on the warm season but a comparison with the thermal comfort conditions in the cool season is made for one of the areas. Air temperature, wind speed, mean radiant temperature (MRT), and the physiologically equivalent temperature (PET) are simulated using ENVI-met to highlight the strengths and weaknesses of the existing urban design. An analysis of the distribution of MRT in the areas showed that the area with low-rise buildings had the highest frequency of high MRTs and the lowest frequency of low MRTs. The study illustrates that areas with low-rise buildings lead to more stressful urban spaces than areas with high-rise buildings. It is also shown that the use of dense trees helps to enhance the thermal comfort conditions, i.e., reduce heat stress. However, vegetation might negatively affect the wind ventilation. Nevertheless, a sensitivity analysis shows that the provision of shade is a more efficient way to reduce PET than increases in wind speed, given the prevailing sun and wind conditions in Dar es Salaam. To mitigate heat stress in Dar es Salaam, a set of recommendations and guidelines on how to develop the existing situation from microclimate and thermal comfort perspectives is outlined. Such recommendations will help architects and urban designers to increase the quality of the outdoor environment and demonstrate the need to create better urban spaces in harmony with microclimate and thermal comfort.
Abstract
Substantial palsa degradation has occurred in Fennoscandia, which is considered to be driven by global climate change. Deeper understanding of the role of different climatic drivers on palsa ...decay, however, is lacking. We use meteorological data and aerial photographs from 1955 to 2016 to statistically identify the most important climatic drivers affecting changes in lateral-temporal palsa decay rates in the largest coherent palsa complex in Sweden, Vissátvuopmi. We show that wetter, warmer and shorter winters are the main causes of large and rapid changes in lateral-palsa extent since the mid-1950s. By analyzing meteorological data from the 1880s to present, we show that average annual temperature conditions have been unfavourable for palsas for more than a century and average annual precipitation conditions have been unfavourable since the 1940s. The decay rates have likely been amplified over the past 50-60 years, and in particular over the most recent decades, due to the combined effect of adverse air temperature and precipitation conditions. Palsa loss is expected to continue, most likely at a higher rate than today, with serious ecological impacts as a consequence.
The main objective of the present study was to examine the influence of culture (Sweden vs. Japan) and environmental attitude (urban vs. open-air person) on participants’ thermal, emotional and ...perceptual assessments of a park, within the physiological equivalent temperature (PET) comfortable interval of 18–23
°C. It was predicted that persons sharing different cultures and environmental attitudes might psychologically differently evaluate a Swedish and a Japanese park despite similar thermal conditions. Consistent with this prediction, Japanese were shown to evaluate the weather as warmer and less good for out-door activity than did Swedes, although and according to the PET index participants in both cultures experienced similar comfortable thermal conditions. Japanese were also shown to evaluate the park as more pleasant and warmer place than did Swedes. However, the Japanese felt emotionally less pleasant at the site than did Swedes. An interaction between culture and environmental attitude indicated tentatively a difference in environmental attitude (urban vs. open-air person) between the two countries as regards the place-related wind sensitivity. All these findings are discussed in terms of culture and environmental attitude suggesting that thermal, emotional and perceptual assessments of a physical place may be intertwined with psychological and cultural processes, rather than fixed by general thermal indices developed in line with the physiological heat balance models.
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.
•Tmrt is a better predictor of heat related deaths than Ta.•Heat related deaths for ages 80+ are primarily attributable to daytime heat stress.•Heat related deaths for ages 45–79 are more ...attributable to night time heat stress.•Tmrt models allow more precise identification harmful of heat stress events.•Tmrt models also allow more precise assessment of urban sites prone to heat.
Health studies have repeatedly used air temperature (Ta), sometimes adjusted for humidity, when analyzing the impact of weather on mortality. The aim of this study is to highlight the importance of mean radiant temperature (Tmrt) and its impact on heat related mortality. Tmrt is an essential meteorological parameter that influences the thermal comfort (heat load) of humans. It is useful when assessing the impact of weather, especially heat, on people’s health. Tmrt is directly influenced by urban geometry and surface material, which also makes it a good measure to identify urban hot spots. The performance of models using Ta and Tmrt for daily mortality is compared for Stockholm County, Sweden. It is demonstrated that Tmrt models fit heat related mortality better than Ta models, which implies that health studies should consider using Tmrt rather than Ta. The use of Tmrt models allows us to determine more accurate thresholds for increased risks of heat related mortality, and thus to better identify adverse weather conditions and heat prone urban geometries. Such information is needed to implement heat-warning systems and mitigate harmful effects of heat stress.
Subjective thermal comfort and outdoor activity in a park and a square in a satellite city northeast of Tokyo were investigated through structured interviews, observations, and comprehensive ...micrometeorological measurements. Results showed that the park was on an average 1.1°C cooler than the square. The relatively warmer thermal conditions in the square in comparison to the park resulted in a heat load of greater intensity for humans in the square. In general, there was a low relation between the thermal environment and the use of the two places in terms of total attendance. However, the use of the park was influenced more by the thermal conditions than by the use of the square, which can mainly be attributed to the different functions of the two places. Finally, examples of the differences between the use of the sun, the attitudes toward it, and outdoor exposure in Japan and Sweden are highlighted and discussed.
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