Search Results (21)

Urban outdoor thermal comfort (OTC) has become an increasingly critical issue under the pressures of urbanization and climate change. Comparative analyses of urban blocks with distinct spatial morphologies are essential for identifying OTC issues and proposing targeted optimization strategies. However, existing studies predominantly rely on microclimate numerical simulations, while comparative assessments of OTC from the human thermal perception perspective remain limited. This study employs the thermal walk method, integrating microclimatic measurements with thermal perception questionnaires, to conduct on-site OTC investigations across three urban blocks with contrasting spatial morphologies—a business district (BD), a residential area (RA), and a historical neighborhood (HN)—in Beijing, a hot summer and cold winter climate city. The results reveal substantial OTC differences among the blocks. However, these differences demonstrated great seasonal and temporal variations. In summer, BD exhibited the best OTC (mTSV = 1.21), while HN performed the worst (mTSV = 1.72). In contrast, BD showed the poorest OTC in winter (mTSV = −1.57), significantly lower than HN (−1.11) and RA (−1.05). This discrepancy was caused by the unique morphology of different blocks. The sky view factor emerged as a more influential factor affecting OTC over building coverage ratio and building height, particularly in RA (r = 0.689, p < 0.01), but its impact varied by block, season, and sunlight conditions. North–South streets generally perform better OTC than East–West streets, being 0.26 units cooler in summer and 0.20 units warmer in winter on the TSV scale. The study highlights the importance of incorporating more applicable physical parameters to optimize OTC in complex urban contexts and offering theoretical support for designing climate adaptive urban spaces. Full article

High-albedo ground and wall materials are promoted to mitigate heat stress in tropical climates, yet conflicting evidence driven by climatic and metric variability make their impact on Outdoor Thermal Comfort (OTC) unclear. This study employed parametric simulations to assess how ground and wall albedo affect OTC, measured via the Universal Thermal Climate Index (UTCI) in typical urban canyons. Using ENVI-met, we tested ground albedo (0.2–0.8) and wall albedo (0.05–0.90) with emissivity fixed at 0.9. Findings reveal that ground albedo had a minimal impact on the UTCI (mean amplitude 0.44 °C), while wall albedo reduced the UTCI by up to 2.80 °C, prioritizing wall material selection for heat mitigation. It was also found that the increase in ground albedo offsets the cooling potential of high-albedo walls. Furthermore, differences in the impact under shaded and unshaded areas were observed. These results question assumptions of universal high-albedo benefits, recommending case-specific simulations in urban design. Full article

Outdoor thermal comfort (OTC) is one of the most important issues for people exposed to urban green space (UGS). It is mainly evaluated by assessing equivalent meteorological factors that may combine and result in human responses of perceptions about comfortable vs. uncomfortable environments. The assessment of these responses is challenged by limits in a database that is powerful enough to support big-data analysis and an essential parameter that can evaluate health-related responses to OTC in urban forests. In this study, a meta-analysis was conducted by synthesizing studies of physiological and psychological health responses of green space (GS) visitors to meteorological factors in host cities on a global scale. A total of 15,000 numerical records about the psychological and physiological responses of UGS visitors were obtained from 105 papers across 68 global cities in 21 countries. A novel parameterization was developed to evaluate OTC by normalizing changes in health-related parameters and detecting their regressions against multiple meteorological factors. It was revealed that OTC resulted in more benefits in psychological health parameters than in physiological ones for UGS visitors worldwide. Globally, health-promoting OTC environments were more found in temperate countries than in countries subjected to other climates. People in Asian countries were indicated to live in environments with higher comfort that benefitted health states in cities at low latitudes. Thermal environments tended to be harsher and more challenging, mostly too chilling, in northern cities than in the south globally. A deep learning model using the ResNet algorithm was found to perform to an expected level with R² as high as >70% and errors controlled generally lower than 0.01. Taking mainland China for instance, it was predicted that thermal environments in eastern cities of China highly challenged the psychological health of local UGS visitors across all seasons of the year. Northern cities of China were predicted to have satisfied thermal environments that benefited psychological and psychological health responses in spring. In summer, cities in West China were predicted to have comfortable thermal environments, and in winter, environments in the southwestern cities were more comfortable. Full article

The health of urban populations is increasingly at risk due to the amplification and chronification of urban heat stress by climate change. This is particularly true for urban environments in humid tropical climates, including many cities in Southeast Asia. It is also in these locations where increasing climatic risks may be exacerbated by urban growth, underscoring the need to develop effective mitigation strategies for strengthening urban resilience and supporting climate change adaptation. Conservation and widespread implementation of green infrastructure (GI) are regarded as one means to counter heat as a public health threat. However, for lower-income countries across Southeast Asia, such as Vietnam, knowledge gaps remain with respect to the effectiveness of greening interventions for heat mitigation. To address this gap, in the context of urban expansion in the humid tropical city of Huế, Vietnam, diurnal cooling potential and regulation of outdoor thermal comfort (OTC) within a wide, shallow street canyon were systematically assessed for selected elements of GI along a quantitative and qualitative dimension using ENVI-met. Tree-based interventions were found to be most effective, potentially decreasing UTCI by −1.9 K at the domain level. Although lower in magnitude, green verges and green facades were also found to contribute to OTC, with green verges decreasing UTCI by up to −1.7 K and green facades by up to −1.4 K locally. Potential synergistic cooling impacts were identified through a combination of GI elements. However, no scenario was found to decrease heat stress to zero or moderate levels. Substantially reducing heat stress may thus require further measures and a closer consideration of local morphological characteristics. Full article

In hot, arid regions, outdoor spaces suffer from intense heat. This study explores how vegetation can improve outdoor thermal performance for pedestrians in low-density residential areas. Specifically, it seeks to identify the best combination of grass and trees for optimal comfort. Four scenarios were simulated using ENVI-met software, varying the proportions of grass and three tree types: 50% grass, 50% grass with 25% trees, 50% grass with 50% trees, and 50% grass with 75% trees. A reference scenario with no vegetation was also investigated. The simulated outputs encompassed air temperature (Ta), mean radiant temperature (T_mrt), relative humidity (RH), and physiologically equivalent temperature (PET). The findings show that scenarios with a higher percentage of trees exhibited the best reduction in air temperature, ranging from 0.2 k to 0.92 k. Additionally, the inclusion of trees and grass in the scenarios resulted in a substantial improvement in thermal performance, with an average reduction of 7.5 degrees in PET. Among the evaluated scenarios, the one comprising 75% trees and 50% grass exhibits the most noteworthy enhancement. This study underscores the significance of strategically positioning vegetation to coincide with prevailing wind patterns, thereby enhancing convective cooling mechanisms and improving overall thermal comfort levels. These insights offer valuable implications for urban planning and the development of sustainable design strategies. Full article

Forecasts of a drastic increase in temperatures in the coming decades are driving the adoption of design strategies and solutions to improve the livability of urban environments. Increasing attention is being paid to the thermal comfort of open spaces by both designers and researchers. Nature-based solutions and man-made devices to improve the comfort of outdoor spaces during summer are spreading, but effective, easy simulation and design support tools for this purpose are still lacking, as most of the available software such as ENVI-met or RayMan cannot model such devices. As Physiological Equivalent Temperature (PET) is one of the most relevant and comprehensive indicators of Outdoor Thermal Comfort (OTC), this study aims to investigate PET variations of different artificial shading systems and propose a simplified methodology for assessing them through analytical simulations with RayMan software. When modeling the shading elements, the trick adopted for this purpose is to associate different cloud densities with the shading provided by the screens, thus overcoming a gap that affects the software. The procedure is digitally tested in a covered courtyard case study in Bologna (Italy). Diverse options proposed by the designers for textile screening materials have been compared, showing that these reduce by at least 1 °C the PET-gauged thermal stress. Beyond specific results, the main outcome of this study is the procedure developed to simulate sun-shading sail effects on OTC by means of RayMan, which can support designers in planning effective solutions for open space livability in summertime. Full article

The worsening urban heat island (UHI) effect poses a great challenge to the thermal comfort of people outdoors. However, there has not been a summary of the mechanisms by which UHI affects outdoor thermal comfort (OTC). This paper reviews the commonly used OTC evaluation indexes, data collection methods, and mitigation measures and discusses the relationship between UHI and OTC. The review is limited to peer-reviewed journal publications found in five databases: Science Direct, Scopus, Google Scholar, PubMed, and Web of Science. The review results indicate that physiological equivalent temperature (PET), universal thermal climate index (UTCI), and wet bulb globe temperature (WBGT) are the most widely used indexes in outdoor thermal comfort studies. The data collection methods mainly include questionnaire surveys, measurement, simulation, and formula calculation. There are four main approaches to mitigating the UHI effect in order to improve the comfort of people outdoors: vegetation strategies, water strategies, urban planning strategies, and material strategies. Future research can focus on developing OTC research methods and indexes and combine thermal comfort with visual comfort, auditory comfort, etc. to better evaluate the overall comfort. Full article

Urban heat islands (UHIs) are negatively impacting the quality of the urban environment and outdoor thermal comfort (OTC) levels, which have raised concerns regarding their impact on urban health and well-being. Understanding of OTC level is crucial, particularly in tropical cities with year-round high temperatures and humidity. A study was conducted in Kuala Lumpur (KL), Malaysia, to determine the OTC level in a selected urban area through microclimate measurements and questionnaire surveys with 1157 respondents. Over half of the urban dwellers reported thermal discomfort, with a high perceived OTC level, indicating strong thermal adaptive behaviours among the urban dwellers despite the physiological stress. Confounding factors such as urban morphology, land cover and human activity patterns also influence the OTC level in the tropical city. The findings emphasize the need for interventions to improve the urban environment and promote better outdoor thermal comfort for city dwellers through measures such as green infrastructure, UHI mitigation and increasing public awareness. Full article

In this study, the physiological and thermal responses of 54 healthy elderly adults during horticultural activities with various intensities (low, moderate, and high) in three typical open spaces were investigated through meteorological measurements, questionnaires, and physiological monitoring. Physiological equivalent temperature (PET), blood pressure, heart rate, oxygen saturation, and ear canal temperature were used as physiological evaluation indices. The results showed that: (1) the proportional changes before and after thermal sensation vote (TSV) and thermal comfort vote (TCV) activities were positively correlated with the spatial characteristics and metabolic levels of outdoor activities in summer; (2) physiological indices were almost constant during low-intensity horticultural activities and significantly different before and after moderate-intensity and vigorous-intensity horticultural activities; (3) when the intensity of horticultural activities changed from low to moderate, the neutral PET (NPET) decreased to 25.29 and 26.82 °C, respectively, whereas the NPET increased to 23.97 °C during vigorous intensity; (4) heart rate (HR) and diastolic blood pressure (SBP) were positively correlated with metabolic rate for the elderly; (5) a moderate sky view factor space was more suitable for the elderly to participate in during outdoor horticultural activities in summer. Full article

Hot-humid areas have long, hot summers and poor outdoor thermal comfort (OTC). The urban heat island (UHI) effect exacerbates the deterioration of OTC in hot-humid areas, seriously affecting the thermal safety of children’s outdoor activities. In this study, 60 scenes were simulated using ENVI-met based on different leaf area index (LAI) and planting arrangements to explore how tree LAI and planting arrangements affect the small-scale thermal environment during hot summer months and to assess OTC using the Universal Thermal Climate Index (UTCI). The research shows that (1) high LAI trees optimize OTC more than low LAI trees, but low LAI trees can be planted multiple times to achieve the level of optimization of high LAI trees; (2) increasing the number of trees optimizes the OTC of the study area, reducing the UTCI by up to 3.7 °C with increased planting compared to unshaded areas; (3) thickening the shade in the east–west direction optimizes the OTC of the study area more than thickening the shade in the north–south direction, with too much north–south shade optimizing the OTC of the study area by only 0.01%. This study provides practical advice for the design of planting in outdoor CAS in hot-humid areas. Full article

Children’s activity spaces in communities designed for children’s recreation are related to children’s safety and physical health. Outdoor thermal comfort of children’s activity spaces in high-density urban residential areas is the key to children’s use in summer. To this end, meteorological measurements and questionnaires were conducted to better understand children’s outdoor thermal comfort in summer, and children’s outdoor thermal comfort was evaluated using the universal thermal climate index (UTCI) for children’s activity spaces in high-density residential areas of Chongqing, China. We draw four conclusions: (1) Different landscape types of children’s activity spaces have different effects on outdoor thermal comfort, and gender differences also affect outdoor thermal comfort in the same type of children’s activity space. (2) Global radiation (G) and air temperature (Ta) were the primary meteorological factors influencing children’s thermal sensations. (3) Outdoor thermal comfort of children’s activity spaces in high-density urban residential areas was inferior overall. (4) Neutral UTCI (NUTCI) for male and female children in Chongqing were 22.2 °C and 21.8 °C, NUTCI ranges (NUTCIR) were 18.4–26.1 °C (male) and 16.2–27.3 °C (female), and acceptable UTCI ranged from 23.2 to 39.1 °C (male) and 22.8 to 40.3 °C (female). The results provide guidance for landscape architects and urban planners in the Chongqing area to create comfortable outdoor spaces for children, improve their physical activity levels, and promote their physical and mental health. Full article

Playgrounds in urban parks are important for children’s physical and mental health, but global warming has led to a worsening outdoor environment and children’s outdoor activities have been affected. Improving the outdoor thermal comfort (OTC) of playgrounds can encourage children to engage in more and safer outdoor activities. However, there are a limited number of studies focusing on preschoolers’ outdoor thermal comfort (OTC) and most of them have substituted children’s thermal comfort with caregivers’ evaluations. To investigate the differences between children’s and caregivers’ evaluations of thermal sensation, thermal benchmarks and thermal adaptive behavior for children, we conducted meteorological measurements on representative playgrounds in three parks in Wuhan, China, and administered thermal perception questionnaires to preschool children and their caregivers. In addition, the Physiological Equivalent Temperature (PET) was used to establish evaluation criteria for children’s OTC and to make recommendations for the improvement of the playground environment. We draw five conclusions by analyzing 719 valid questionnaires: (1) Children were less sensitive to changes in meteorological factors than caregivers and had better tolerance of cold environments. (2) The NPET for preschoolers was evaluated by children and by caregivers, respectively, as 22.9 °C and 22.3 °C in summer and 10.6 °C and 11.2 °C in winter. (3) Playgrounds in Wuhan’s parks are uncomfortable for a long time in summer and a short time in winter. (4) Both children and caregivers want to improve summer comfort by lowering the temperature and winter comfort by increasing solar radiation. At the same time, children and caregivers show different preferences in adaptive behavior choices. (5) Adding deciduous trees and water play facilities can improve the site thermal environment. Furthermore, the OTC of humans can be improved by adding more service facilities on playgrounds. Full article

A comfortable thermal environment in outdoor spaces is beneficial to people’s physical and mental health in cold conditions during winter. Greenery can improve outdoor thermal comfort (OTC) via microclimates in winter. Multiple methods have been employed to investigate how greenery influences OTC and microclimate. However, the underlying mechanism of how microclimate participates in the regulation of the effect of greenery on OTC is unclear. To examine the mediating effect of microclimate on the relation between greenery and OTC in cold weather during winter, we conducted meteorological measurement and thermal comfort surveys in Zhengzhou, a city in China’s cold region, from 29 to 30 December 2019. Two objective greening indices from different dimensions were extracted at twelve sampling points: (1) the green view index (GVI) from horizontal normal images from people’s perspective, and (2) the tree view factor (TVF) from vertical-upward fisheye images. With microclimatic parameters as the mediators, a comprehensive multi-step mediation analysis was conducted. The regression results revealed that the GVI and TVF were negatively associated with the thermal comfort vote (TCV) (i.e., the more greenery, the less TCV, which means the more comfortable the thermal environment). Our findings show that both GVI and TVF contribute to OTC through different mechanisms in cold climatic conditions during winter. Vegetation in sight revealed by the GVI can directly regulate OTC by affecting people’s mental feelings or other factors. Air temperature (Ta), relative humidity (RH), and wind speed (Va) served as significant partial mediators for the GVI. Moreover, there was a complete mediation for TVF–OTC correlation with Ta, RH, and Va as significant mediators. The mediating effects of microclimate accounted for 81.00% for GVI and 89.02% for TVF, respectively. The GVI is propitious to the study of people’s mental health and landscape preferences, whereas TVF is suitable for studies on microclimate adaptation. Full article

The objective of this paper is to show a study on the influence of vegetation on the outdoor thermal comfort (OTC) of a high-altitude tropical megacity. The OTC is evaluated by the PET (Physiological Equivalent Temperature) index and by establishing three simulation scenarios: (i) Current OTC, (ii) OTC under RCPs 4.5 and 8.5 (Representative Concentration Pathway), and (iii) OTC under RCPs and ENSO (El Niño–Southern Oscillation). The results show that the hourly variation range of the current OTC in urban areas with vegetation is greater (+3.15 °C) compared to impermeable areas. Outdoor thermal stress due to cold in vegetated areas is 1.29 °C lower compared to impervious areas. The effect of vegetated coverage on the improvement of urban OTC increases as the phenomenon of global warming intensifies. On average, in the current, RCP4.5, and RCP8.5 scenarios for each 10% increase in urban vegetation coverage, an increase of 0.22, 0.24, and 0.28 °C in OTC is obtained, respectively. The hourly variation range of the PET index increases during the ENSO scenario (vegetated areas: +16.7%; impervious areas: +22.7%). In the context of climate change and variability, this study provides a reference point for decision-makers to assess possible planning options for improving OTC in megacities. Full article

Decision makers (DMs) who are involved in urban planning are often required to allocate finite resources (say, money) to improve outdoor thermal comfort (OTC) levels in a region (e.g., city, canton, country). In this paper, for the first time, we address the following two questions, which are directly related to this requirement: (1) How can the statistical properties of the spatial risk profile of an urban area from an OTC perspective be quantified, no matter which OTC index the DM chooses to use? (2) Given the risk profile, how much and where should the DM allocate the finite resources to improve the OTC levels? We answer these fundamental questions by developing a new and rigorous mathematical framework as well as a new class of models for spatial risk models. Our approach is based on methods from machine learning: first, a surrogate model of the OTC index that provides both accuracy and mathematical tractability is developed via regression analysis. Next, we incorporate the imperfect climate model and derive the statistical properties of the OTC index. We present the concept of spatio-temporal aggregate risk (STAR) measures and derive their statistical properties. Finally, building on our derivations, we develop a new algorithm for spatial resource allocation, which is useful for DMs and is based on modern portfolio theory. We implemented the tool and used it to illustrate its operation on a practical case of the large-scale area of Singapore using a WRF climate model. Full article