Assessment of UHI mitigation strategies on indoor and outdoor thermal comfort under future extreme heat and power outage conditions, case study: educational building in Shahrood, Iran

Human thermal comfort is influenced by different climatic parameters. The effect of rain and snow events on human thermal comfort has been less explored in the available literature. The work presented here investigates outdoor and indoor thermal comfort using the physiological equivalent temperature (pet) and wind chill temperature (WCT) indices and Givoni bioclimatic chart for rainy and snowy days as well as a day prior to and a day post snow and rain events in Ardabil. Results indicated that snow and rain events have cooling effects on both indoor and outdoor thermal sensation. The cooling effect of rainy and snowy days is higher than a day prior to and a day post events. Also, the cooling effect of the snow and rain increases by the intensity of the events (> 10 mm/day). Based on the PET and WCT outputs, the cooling effect of the snow events with intensity higher than 10 mm a day is about 1.77 and 0.80 °C less than events under 10-mm a day intensity. The same pattern was observed for rain events. Analysis of the cooling effect of event duration on outdoor thermal comfort indicated that the events with more than 2-day duration have more cooling effect on thermal sensation. Finally, due to different cooling effects of snow and rain events on indoor thermal sensation, different types of bioclimatic strategies should be used inside the buildings during snowy and rainy days in Ardabil.

Introduction The intensification of Urban Heat Islands (UHIs) is increasing urban thermal risk, with heat-related impacts unevenly distributed across populations. In informal settlements, precarious infrastructure, high occupancy densities and limited access to green spaces often converge. Under these conditions, heat stress is frequently experienced as everyday thermal discomfort and remains a persistent yet under-recognised threat to well-being and public health, receiving limited attention in both policy and practice. In this context, spatial design plays a central role in enhancing outdoor thermal comfort, with Nature-based Solutions (NbS) emerging as key strategies for climate mitigation and adaptation. However, evidence remains limited on how vegetation and shading configurations translate into measurable thermal performance at the micro-urban scale, particularly in Latin American informal-settlement upgrading contexts. Methods This study examines the contribution and limitations of NbS for outdoor thermal comfort within an informal-settlement upgrading process in Buenos Aires, Argentina. The analysis focuses on two pedestrian passageways, Teresa Rodríguez and Eva Estela Carrizo, in Barrio 20, currently undergoing a comprehensive re-urbanization process. As part of a climate-focused research-action initiative, both passageways were subject to pilot NbS interventions co-designed through participatory processes. While sharing a similar southeast -northwest orientation, they differ markedly in morphology, spatial configuration and urban origin, enabling a comparative assessment of NbS performance under contrasting conditions. Outdoor thermal comfort was assessed through microclimatic simulations and quantified using the Universal Thermal Climate Index (UTCI) across three scenarios: a pre-intervention baseline, a current post-intervention scenario, and a desirable medium-term future scenario incorporating vegetation growth and further NbS strategies. Simulations were conducted under both typical summer conditions and extreme heatwave events. Results Results indicate that NbS can substantially reduce pedestrian-level thermal stress, particularly under extreme heat conditions. While post-intervention effects differ between the two passageways, future-oriented scenarios reveal substantial cooling potential, reaching the UTCI category No Heat Stress under typical summer conditions and Moderate Heat Stress during heatwaves. Discussion These findings provide comparative evidence to inform urban planning practices and the revision of regulatory frameworks in informal-settlement upgrading processes. In doing so, they highlight that NbS performance is context-dependent, reflecting the combined influence of morphological and climatic conditions as well as institutional and socio-cultural factors, such as community acceptance. This also underscores the role of microclimatic simulation as a decision-support tool in advancing climate-responsive and equity-oriented urban transformation.

Feeling the heat in sport

A quantitative evaluation model of outdoor dynamic thermal comfort and adaptation: A year-long longitudinal field study

• ENVI-met parameterisation incorporating field- and laboratory-derived soil data advances OTC modelling beyond standard database inputs. • ENVI-met modelling reveals significant OTC differences across LCZs of Ljubljana. • Mean OTC varies by up to 12.44 °C between LCZs on hot summer days. • Tree shade reduces heat stress by up to 8.43 °C in Ljubljana's urban landscape. Owing to the specific thermal conditions of the urban environment, such as a high proportion of impervious surfaces, low tree cover, high building density, and low surface albedo, residents in these areas experience altered outdoor thermal comfort (OTC). Although these conditions generally contribute to elevated heat stress during hot summer days, this phenomenon varies spatially and temporally. Numerous studies have examined OTC indices across different cities using various modelling techniques; however, the preparation of spatial input data is often insufficiently addressed. Therefore, the study aims to quantify and assess OTC across selected Local Climate Zones (LCZs) in Ljubljana, as well as the effect of existing tree shading on OTC improvement, by advancing a modelling workflow that explicitly incorporates detailed field-derived urban soil characteristics into ENVI-met simulations. This was achieved through interdisciplinary field and laboratory measurements combined with urban microclimatic modelling. The fieldwork included micrometeorological measurements, soil sampling, surface albedo measurements, and green infrastructure mapping. The results revealed statistically significant differences in Universal Thermal Climate Index (UTCI) and Physiological Equivalent Temperature (PET) indices between 13:00 and 15:00 local time across the LCZs. LCZ A exhibited the lowest levels of heat stress, whereas LCZ 8 experienced the highest. The average differences in UTCI and PET between these two zones were 9.23 °C and 12.44 °C, respectively. Further analysis demonstrated that existing tree shade significantly improved OTC. Across all LCZs, the average thermal comfort improved by 5.67 °C (UTCI) and 8.43 °C (PET) under tree shade compared to areas exposed to direct solar radiation.

As a main place for student activities on campus, outdoor spaces have positive impacts on students’ physical and mental health. Namely, outdoor heat and comfort are of great significance to improve activity quality. Here, four unique outdoor spaces were studied to explore the varying effects on human thermal comfort during hot-summer and cold-winter periods. Distinct outdoor spaces (fully open, semi-open, semi-enclosed, and fully enclosed areas) from the southern campus of Anhui Jianzhu University were chosen. The PET was used as a metric for measuring thermal comfort and analyzing correlated spatiotemporal distributions. The results showed that outdoor thermal comfort was derived from multiple factors, including vegetation, underlying surface materials, building presence, and wind-heat environment. Notably, high correlations between Tmrt and thermal comfort were revealed, where such temperatures of places with trees or building shade were low; thus, PET was low. Further, Ws showed a significantly negative correlation with PET. Of the four outdoor space forms, the fully enclosed location had the lowest thermal comfort level, while the semi-enclosed spaces showed the highest level of body comfort. Therefore, semi-enclosed space (U-shaped) is recommended in campus planning and construction. Accordingly, an improved strategy was proposed based on experimental transformation for fully enclosed spaces. The thermal comfort after optimization was simulated to provide references for outdoor space thermal comfort improvement during seasonal extremes.

Outdoor thermal comfort is an important criterion for evaluating the quality of outdoor activity environments and is also a significant indicator for assessing sustainable building design. Over the past century, more than 165 indoor and outdoor thermal comfort indexes have been developed to define human thermal comfort conditions under various circumstances and to quantify indoor and outdoor thermal environmental conditions. However, in the process of outdoor thermal comfort indicators becoming widely used worldwide, it remains a pressing research issue to compare the current state of application in China and other countries, identify the key areas of application for both sides, and outline the trends in outdoor thermal comfort index application. This study analyzed 346 articles on outdoor thermal comfort indicators. Employing bibliometric methods, we outline the general landscape of outdoor thermal comfort index applications in China and other countries. Additionally, we utilize comparative analysis to uncover similarities and differences in the research focus on outdoor thermal comfort. The research findings indicate the following: (1) Compared to China, other countries started outdoor thermal comfort index application research earlier. Their papers have higher average citation counts and engage in close academic collaborations. However, the quantity of published papers is fewer than in China. (2) The top five frequently used indexes in both China and other countries are PET (including mPET), UTCI, PMV, SET* (including OUT_SET*), and THI (including DI). China tends to use PET and UTCI more frequently than other countries. (3) The potential future directions for outdoor thermal comfort index applications in both China and other countries include: “monitoring and controlling regional outdoor thermal comfort at the temporal and spatial scales”, “multi-factors coupling effects on outdoor thermal comfort”, “human health assessment and prediction based on outdoor thermal comfort”, and “utilizing computational algorithms to calculate outdoor thermal comfort”. This study can serve as a reference for researchers and designers in the industry, contributing to the creation of sustainable outdoor environments.

Linking landscape spatial heterogeneity to urban heat island and outdoor human thermal comfort in Tokyo: Application of the outdoor thermal comfort index

How green building rating systems affect indoor thermal comfort environments design

The effect of Urban Heat Island mitigation strategies on outdoor human thermal comfort in the city of Baghdad

Assessing the vertical synergies between outdoor thermal comfort and air quality in an urban street canyon based on field measurements

Data-driven approach to develop prediction model for outdoor thermal comfort using optimized tree-type algorithms

Outdoor thermal comfort is influenced not only by meteorological variables air temperature, radiation and humidity at regional and local scales but also by local parameters such as mean radiant temperature and wind patterns, which vary at meter-scale within cities. All these factors can be affected by ongoing climate change. Hence, modelling future thermal comfort requires a multi-scale approach. Thermal comfort in outdoor settings can be quantified and described by thermal indices such as the Universal Thermal Climate Index (UTCI), which reflects the human response to environmental and physiological forcing. To date, several microscale modelling approaches have been proposed to model the meteorological and geometric variables that contribute to the UTCI, but they are all highly detailed, complex and computationally intensive. As a result, only individual heat waves, short case studies or single points have been modelled to estimate future heat stress conditions in cities. This study introduces a novel and efficient deep-learning model that instantly and accurately predicts thermal comfort maps across entire cities and for long periods. This model is unique in its adoption of a solitary deep learning architecture, avoiding the use of sub-models that separately model, for example, air temperature or wind speed. We will refer to this model as the Unified Human Thermal Comfort Neural Network (UHTC-NN). Training and evaluation of the UHTC-NN is based on a machine learning model from a previous study, which combines four sub-models modelling air temperature, mean radiant temperature, wind speed, and relative humidity into UTCI. The UHTC-NN has a mean absolute error of 0.5 K compared to its preceding model. The UHTC-NN enables new applications of thermal comfort modelling, including meter-scale urban climate projection to support climate adaptation management in cities. In a case study, we apply UHTC-NN to downscale 15 EURO-CORDEX climate projections with a 3-hour resolution over 30 years to generate high-resolution (1x1 m) street-level outdoor thermal comfort maps for the city of Freiburg, Germany. We compare the changes in UTCI frequency distribution and uncertainties of three different Representative Concentration Pathways (RCP2.6, 4.5 and 8.5) for the years 2070-2099 with the historical climate (1990-2019). Our study models the entire city center of Freiburg, with a domain size of 2.5x2.5 km, covering various aspects of the city's urban form. We show that the average number of hours per year with strong to extreme heat stress (UTCI >= 32°C) will increase up to three and six times for RCP2.6 and RCP8.5, respectively. The number of night-time hours with UTCI >= 20°C will increase by a factor of two and five, respectively for RCP2.6 and RCP8.5, compared to the 1990-2019 period. In addition, the 80th UTCI percentile shifts by 2°C and 4°C for RCP2.6 and RCP8.5, respectively. The presented high-resolution urban climate simulations allow us to identify intra-urban variability and daytime / nocturnal hot-spots where climate change will have the greatest impacts on outdoor thermal comfort. Such urban climate simulations therefore allow for an effective selection of areas where climate adaptation needs to be prioritized.

Buildings’ outdoor thermal comfort influences environment quality and human behavior in urban neighborhoods. The Universal Thermal Climate Index (UTCI) has been broadly applied to the study of buildings’ outdoor thermal comfort in urban areas. However, complex environmental conditions in climate-sensitive urban areas can make UTCI assessment complicated and ineffective. This paper introduces digital techniques into buildings’ outdoor thermal comfort analysis for the improvement of the urban habitant environment. A digital simulation system is generated to facilitate the analysis procedure for buildings’ outdoor thermal comfort assessment in urban neighborhoods. The analysis addresses the research question: “Can digital simulation techniques provide a modeling system to assess buildings’ outdoor thermal comfort continuously and effectively?” Methods include a case study of neighborhoods in Beijing, qualitative and quantitative analysis based on digital processes, and parametric modeling. The results indicate that digital simulation techniques and tools have the capability to support the analysis of buildings’ outdoor thermal comfort by providing three-dimensional models, algorithm-based analysis, and visual simulation. The findings include a critique of digital simulation as applied to architecture study and insights on potentially improving buildings’ outdoor thermal comfort through human–computer interactions.

Passive design strategies to improve student thermal comfort in Assiut University: A field study in the Faculty of Physical Education in hot season