Universal Thermal Comfort Index Research Articles

Investigating outdoor thermal comfort variations across Local Climate Zones in Nagpur, India, using ENVI-met

Increasing temperatures are exacerbating the urban heat island effect within urban areas. As thermal stress rises in these environments, evaluating the variation in thermal comfort across the city is crucial for designing thermally comfortable spaces. Nagpur, a centrally located city in India experiences extreme thermal stress during the summer. The present study focuses on assessing the variation in thermal comfort using indices such as air temperature (AT), physiological equivalent temperature (PET), and universal thermal comfort index (UTCI) which acknowledge energy balance in the human body and its relationship with the outdoor environment. These indices are calculated across ten areas in the city, identified by Local Climate Zone (LCZ) using ENVI-met. The 24-h simulations revealed that open and vegetated urban areas (LCZ 6, 6B & A) present low heat stress during 14:00–15:00 and 03:00–04:00. However, sparsely built areas (LCZ 9 & 93) experience extreme thermal stress during daytime and moderate stress during nighttime. Densely built areas (LCZ 3 & 3F) present moderate thermal stress during the daytime and the highest during nighttime. Further, PET and UTCI percentile assessments revealed that sparsely built areas experience both extreme and neutral thermal stress. Compact areas stay moderately warm during nighttime. Vegetated areas experience moderately high thermal stress during the daytime and neutral to warm thermal stress during nighttime. The study highlights the need for more emphasis on nighttime thermal stress using ENVI-met to assess thermal conditions across various urban settings. This will contribute to a better understanding of climates and locations experiencing extreme thermal stress.

Remote Sensing-Based Outdoor Thermal Comfort Assessment in Local Climate Zones in the Rural–Urban Continuum of eThekwini Municipality, South Africa

Due to the need to continuously monitor and understand the thermal environment and its socioeconomic implications, this study used remotely sensed data to analyze thermal comfort variation in LCZs, including along the rural to urban gradient of the eThekwini Municipality in KwaZulu-Natal province of South Africa. LCZs were mapped using multi-temporal and multi-spectral Landsat 8 and Landsat 9 data using the approach by World Urban Database and Access Portal Tools (WUDAPT), while thermal data were used to retrieve land surface temperatures (LSTs). Data for training classification of LCZs and accuracy assessment were digitized from GoogleEarth guided by knowledge gained and data collected during a field survey in March 2022 as well as pre-existing maps. LCZs were mapped using the random forest classifier in SAGA GIS software while a single channel algorithm based on band 10 was used to compute LST for different scenes. The LSTs were adjusted and further used to derive thermal comfort based on the Universal Thermal Comfort Index (UTCI) categories as an indicator for outdoor thermal comfort on the extremely low- and extremely high-temperature periods in the cool and hot seasons, respectively. LCZs were mapped with high accuracy (overall accuracy of 90.1% and kappa of 0.88) while inter-class separability was high (>1.5) for all LCZ pairs. Built-up LCZs dominate the eastern parts of the municipality, signifying the influence of the sea on development within the area. Average LST was coolest in the dense forest, open low-rise and water LCZs in the cool and hot seasons, respectively. The compact high-rise LCZ was the warmest in both the hot (36 °C) and the cool (23 °C) seasons. The sea sands were among coolest regions in both seasons due to their high water content, attributed to their high water table and close proximity to the ocean. There was no thermal stress during the cool season, while most areas recorded moderate to strong heat stress in the hot season. Some areas in the densely built-up LCZs recorded very strong heat stress in the hot season. The findings suggest that policies and strategies should enhance heat mitigation capacities in strong-heat-stress areas during the hot season. Municipal authorities and citizens must work together to build strategies to minimize temperature extremes and associated socioeconomic pressures. Urban development policies, plans and strategies should consider implications on the thermal environment as well as the value of conservation of LCZs with high-heat mitigation value such as dense forests and expansion of built-up LCZs with low-heat absorption levels such as open low-rise. The study was based mainly on remotely sensed temperatures with some ground data used to validate results, which may limit the assessment. Overall, the study provides insights towards achievement of global sustainable and climate-smart development targets.

Cool roof strategies for urban thermal resilience to extreme heatwaves in tropical cities

Extreme heatwaves in tropical cities represent a significant short-term weather challenge, directly impacting urban heat, exacerbating human discomfort, and increasing energy demands. To alleviate this, meteorological adjustments utilizing reflective roofing technologies, such as cool roofs, can effectively mitigate heatwave-induced excess heat and enhance thermal comfort. This study assessed the effectiveness of cool roofs in cooling urban areas following heatwaves in Kolkata, India, using comprehensive city-scale simulations. The study presumed that the existing roofing materials, with a reflectivity of 0.15 and emissivity of 0.85, indicated the unmitigated condition. These materials were replaced with third-generation cool roof materials featuring a reflectivity of 0.80 and emissivity of 0.85, leading to a substantial improvement in urban meteorology and thermal comfort compared to the unmitigated state. Notably, during heatwave episodes, the most significant computed reductions in energy flux were 181.3 Wm−2, 16.6 Wm−2, 56.3 Wm−2, and 251.9 Wm−2 for sensible heat, latent heat, ground storage, and net inflow radiation, respectively. Consequently, this led to decreases of 2.3 °C, 6.1 °C, 21.8 °C, and 1.9 °C in urban thermal parameters during peak hours (14:00 LT) for ambient temperature, surface temperature, roof surface temperature, and urban canopy temperature, respectively. The maximum drops in the planetary boundary layer (PBL) were 130.6 m, 1978.5 m, and 1010.3 m for 6:00 LT, 14:00 LT, and 18:00 LT, with an average of 870.3 m. Cool roofs demonstrated their potential to minimize thermal stress during heatwave periods, showcasing a maximum drop in the heat stress index (HSI) of up to 1.5 °C in the morning. Furthermore, outdoor thermal comfort could be significantly enhanced by lowering the universal thermal comfort index (UTCI) at the near surface, resulting in reductions of up to 1.8 °C during peak hours. On average, there was a reduction in UTCI between day and night of approximately 1.2 °C and 0.7 °C in densely populated urban areas. Additionally, the study evaluated 32 case studies that focused on cool roof strategies, revealing remarkably consistent findings that suggest a plausible justification. These findings provide a valuable framework for urban planners and policymakers considering the integration of cool roofs-based heat reduction technology at the city scale.

Retrofit strategies to mitigate overheating linking urban climate modeling and urban building simulations with outdoor comfort. An urban sector in Malaga (Spain)

This work evaluates the cooling effect of retrofit strategies on urban buildings and outdoor comfort in an urban sector in Málaga on one of the hottest days. The methodology links urban climate modeling and urban building simulations with outdoor comfort. The solar reflectance (SR) of roofs, urban surfaces and green areas and their forestation increases after the retrofit. Only the SR façade remains the same, be it in the current or the retrofit scenarios: 0.3. Both façade retrofit strategies consist of an opaque double skin façade (ODSF) with ceramic or metal tiles. Energy cooling is reduced by 52.51% with ceramic and by 52.57% with metal ODSF while urban comfort improves after retrofit: Universal Thermal Comfort Index (UTCI) decreases by 0.62 °C and Mean Radiant Temperature (MRT) decreases by 2.58 °C. Simultaneously, seven points at the pedestrian level assess outdoor comfort in different urban canyons. UTCI decreases more with the metal than with the ODSF ceramic. Regardless the canyon height, the width ratio or the orientation, the UTCI decreases between 2.45 °C and 4.86 °C when under a tree and it decreases more as S/N canyons narrow. This methodology and insights help stakeholders, designers, planners, and policy-makers make data-driven decisions to mitigate overheating and UHI in Mediterranean cities with similar urban building and canyon morphology.

Land use and land cover dynamics: Implications for thermal stress and energy demands

This study examined the interaction between land use and land cover (LULC) dynamics, trend and thermal stress distribution using the universal thermal comfort index (UTCI) and different LULC classifications under two Coupled Model Intercomparison Project Phase 6 (CMIP6) Shared Socioeconomic Pathways (i.e., SSP 370 and 585) climate and land use scenarios for the historical (1959–2014) and future period (2045–2100). The moderate to strong cold stress in the annual and winter climatology in the midlatitudes was replaced by no thermal stress in the summer, while the summertime ranged from moderate to strong heat stress. A negative correlation was observed between thermal stress and southern hemispheric primary forests. Perennial croplands had the most dynamic changes in intensity during the historical period. Primary and secondary forests had an active influence on global thermal stress. Areas in the tropics recording moderate heat stress coincided with secondary nonforest, pastureland, and annual cropland expansions. The conversion of forest to range land and croplands and the subsequent negative forest trends increased the severity of thermal stress. The future projection showed intense thermal stress; however, the SSP-585 signals were more potent. As a result, cooling demands will rise, and heating demands will decline, yet, improved thermal comfort necessitates a higher cooling capacity, especially in the summer. Thermal stress may make it difficult for many cooling systems to meet people's energy demands. These could be a driving factor in shaping better land use policies, improving energy demand preparedness, and elucidating the potentially severe impacts of thermal stress.

Assessment of overhead environments on pedestrian thermal comfort in a dense urban district

Outdoor thermal comfort in urban environmental settings is often investigated at a small scale, e.g., in street canyons. Yet, pedestrian thermal comfort in a district is scarcely assessed, especially in terms of the comprehensive overhead environments such as sky openness, green coverage, and sun exposure. This study provides a systematic methodology to quantify the district-scale pedestrian thermal comfort performance considering overhead environments. Mobile transects were designed for data collection during peak hot hours within a medium-scale district. A portable weather station was used to measure outdoor thermal environments and a fisheye lens was to capture hemispherical images of overhead environments. A universal thermal comfort index, Physiological Equivalent Temperature (PET), was subsequently calculated with the collected thermal environment data. Meanwhile, hemispherical images were segmented into areas of visible sky, overhead greenery, and sun, which were further weighed into corresponding view factors. Eventually, a multiple regression model was developed between PET and view factors together with meteorological variables. The results showed that a decrease in the sky view factor of 0.17 or an increase in the green view factor of 0.21 could reduce PET by 0.5°C. The findings scientifically support resilient urban planning in greening and cooling urban dense spaces for comfortable and liveable environments.

Development of an integrated index to quantify thermal comfort and walkability in urban areas

Although outdoor thermal comfort is extensively investigated in urban areas, the measures are barely focused to determine the walkability through these spaces. Therefore, a space with a high level of thermal comfort can experience a low level of pedestrian agglomeration while a space with a low level of thermal comfort can be massively used by inhabitants. Therefore, the solution to urban design and planning can be significantly altered if both dimensions are simultaneously taken into the account. This study investigates the relationship between spatial configuration and thermal comfort potential to evaluate the effect of spatial configuration on outdoor environmental quality. For this purpose, a framework is developed to understand the impact of built urban areas on thermal comfort and space syntax performance using a high-resolution spatial model to simulate the correlation of thermal comfort and betweenness centrality of a case study neighbourhood in the hot and humid climate area of Al-Khobar in Saudi Arabia. The mixed-use neighbourhood is analysed by the universal thermal comfort index and several space syntax metrics. The presented study uses Grasshopper environment and Ladybug and Decoding Spaces tools. The simulation study expressed that significant changes in orientation and buildings heights have a remarkable effect on improving OTC and space syntax in the urban neighbourhood.

North Eurasian thermal comfort indices dataset (NETCID): new gridded database for the biometeorological studies

Global climate changes give us the important task of obtaining information about the spatial distribution of bioclimatic comfort indicators at the global or continental level. One of the most applicable tools can be based on reanalysis data (meteorological gridded data with global coverage). This issue is fully relevant for the territory of Northern Eurasia with its diverse climates, rapid environmental changes, and often sparse network of in situ observations. In this paper, we present a conceptually new dataset for the most popular thermal comfort indices, namely heat index (HI), humidex (HUM), wind chill temperature, mean radiant temperature, physiologically equivalent temperature (PET) and Universal Thermal Comfort Index (UTCI) derived from ERA-Interim reanalysis hourly data for the territory of Northern Eurasia (the area limited by 40° N–80° N, 10° W–170° W). The dataset has horizontal resolution of 0.75° × 0.75° (up to 79 km), temporal resolution of 3 h, and covers the period from 1979 to 2018 (40 years), which corresponds to the standard of the World Meteorological Organization in determining the parameters of the modern climate. Time series of indices are supplemented with a set of 8092 pre-calculated statistical parameters characterizing climatology of the thermal stress conditions. We further present several examples of the North Eurasian Thermal Comfort Indices Dataset (NETCID) data application, including analysis of the spatial heterogeneity of thermal stress conditions, assessment of their changes and analysis of specific extreme events. Presented examples demonstrate a pronounced difference between considered indices and highlight the need of their accurate selection for applied tasks. In particular, for the whole study areas HI and HUM indices show much smaller thermal stress repeatability and weaker trends of its changes in comparison to PET and UTCI indices. NETCID is available for free download at https://doi.org/10.6084/m9.figshare.12629861.

Increased risk of heat stress conditions during the 2022 Comrades Marathon

The Comrades Marathon is South Africa’s – and the world’s – most recognised and largest ultra-marathon event, with over 15 000 participants from across the globe competing in the 89-km road running event each year. Historically, the event has been held before the start of austral winter (20 May – 17 June). However, in 2022, organisers of the race moved the event to 28 August, when austral spring commences. We explore the climate, in particular the Universal Thermal Comfort Index (UTCI), of past Comrades events (1980-2019) and compare these data to UTCI data of the new proposed date (28 August) for the same period. The climatology for May, June, July and August was determined to identify periods with the lowest risk for ‘strong’ to ‘very strong’ heat stress. Results show that participants’ risk of exposure to ‘strong’ heat stress and ‘very strong’ heat stress periods will be more likely if the event is held in August as compared to the original event dates. Therefore, it is concluded that mid-June to mid-July has the lowest risk of heat stress exposure along the route. Runners and organisers should be aware of the higher risk of exertional heat illness during the 2022 Comrades Marathon to ensure safe participation. Significance: The new proposed date for the Comrades Marathon will increase the risk of exposure to ‘strong’ and ‘very strong’ heat stress conditions, as defined by the Universal Thermal Comfort Index (UTCI). The UTCI indicates that mid-June to mid-July has the lowest risk of heat stress exposure at the three reference points along the route. Organisers should warn runners of the higher risk of exertional heat illness due to the possible exposure to high UTCI values or more unfavourable climatological conditions. Furthermore, runners should be informed of a variety of preventative strategies to ensure safe participation.

Suitability of Thermal Indices in Describing Heat Stress Compensability

Multiple thermal indices have been created to categorize the impact of the ambient environment on human physiology and health. Many of these indices promulgate thresholds that are used to delineate between safe and unsafe thermal environments at rest and during physical activity (exercise, sport, industry, etc.). While some of these thresholds were empirically derived, others were established based on models or theoretical construct with no objective physiological measurements or rationale. In a world where heat is already the leading weather‐related cause of death and climate change will exacerbate the effects of extreme heat in the future, it is important to determine if commonly used indices and associated thresholds are able to accurately describe ambient conditions which are thermally safe or unsafe. One physiologically‐ and biophysically‐determined definition of safe environments is based on the upper limit of thermal balance (PSU H.E.A.T. Project). In the present study, young, healthy adults were exposed to a progressive heat stress protocol in an environmental chamber in both hot‐dry and warm‐humid conditions to determine critical environmental limits of dry‐bulb temperature and vapor pressure which could then be compared to other widely used critical heat stress index values. That is, upper environmental limits for human heat balance were compared to common heat stress indices, including wet‐bulb temperature (Twb), Heat Index (HI), Wet Bulb Globe Temperature (WBGT), and Universal Thermal Comfort Index (UTCI). Under activities of daily living, HI and WBGT thresholds very nearly match up with heat stress compensability curves based on critical heat balance limits while large variation was found in with UTCI. Interestingly, the theorized Twbthreshold of 35°C, used increasingly by mainstream media sources in describing extreme heat, was significantly higher than the critical limit for heat stress compensability. This work highlights the need for continued empirical work in determining and validating existing critical heat stress index thresholds as well as the need for better communication to the general public of what each heat stress index means for their environmental health and safety in a warming world.

Thermal Comfort-Based Spatial Planning Model in Jakarta Transit-Oriented Development (TOD)

Transit-oriented development (TOD) is integrated spatial planning and transportation that enhances walkability and other green mobility. The issue of thermal comfort in walkability is a major concern in the TOD of cities in tropical climates such as Jakarta. This study aimed to model and compare microclimate conditions and thermal comfort between existing conditions and TOD spatial planning scenarios. The microclimate condition was modeled using ENVI-met, and thermal comfort was analyzed following the physiologically equivalent temperature (PET) and universal thermal comfort index (UTCI). The results of microclimate modeling showed that the average minimum temperature of the current condition was lower than the TOD at 0.149 °C; meanwhile, the average maximum temperature of the current condition was higher than the TOD at 0.761 °C. Furthermore, the results of the PET and UTCI calculation between the existing land use and the TOD plan scenario showed that both the minimum and maximum PET and UTCI values of the TOD plan scenario throughout the modeling time were lower than the existing conditions. In conclusion, the urban canyon formed by the designed TOD scenario resulted in lower wind speed than the existing condition. However, this factor potentially does not impact the increase in the urban heat island effect in the TOD area since the effect of shading the area by the high-rise building lowers the temperature.

Future impact of cloudiness and wind changes on thermal comfort conditions in the city of Tabriz (Iran) in the frame of climate change

• Cooling effect of the wind will decrease with time in Tabriz. • Thermal comfort must be incorporated in urban planning strategies. • Changes in cloudiness is a key factor for thermal comfort in Tabriz. Climate change will alter thermal comfort very differently depending on the future scenario selected. This research computes two bioclimatic indices: Physiological Equivalent Temperature (PET) and Universal Thermal Comfort Index (UTCI), in the area of Tabriz (Iran), considering an observational period (1960 to 2020) and three projected scenarios (RCP2.6, RCP4.5, and RCP8.5) associated to greenhouse gas concentrations for the period 2030 to 2059 and 2060 to 2100. The CanESM2 model was used to estimate projected data. Thermal comfort for these three periods are compared at daily basis attending to the sky conditions (clear and cloudy) and the presence or absence of wind. The study of the observational period shows that the cloud cover effect has increased PET and UTCI values by 0.82 and 0.51°C, respectively. For the projected period, it has been found an increase in PET and UTCI values by 0.36 and 0.42°C associated to the presence of clouds. On the other hand, a decrease in temperature of 10°C for PET and 11.73°C for UTCI is found in the observational period when windy and calm days are compared. This cooling effect of the wind will decrease in the projected period where temperature reduction based on PET and UTCI values is estimated to be 4.5 and 8.4°C for 2030-2059 and 2.5 and 5.2°C for 2060-2100 respectively. In conclusion, future changes in clouds and wind will clearly impact thermal comfort in the city of Tabriz in the future decades. Both the projected cloudy heating effect and the reduction of the potential of cooling of the wind, will have serious implications for heat-related diseases and different socioeconomic activities in the region. Accordingly, the definition of mitigation and adaptation strategies in short term should be a priority.

도시내 폭염 대응사업의 온도저감 효과 추정에 관한 연구

In this study, to determine areas with high thermal stress in the city of Cheongju and properly respond to damage from heat waves, the scenarios of roof greening, cool roofs, cooling fog, clean roads, and urban green spaces were considered. Using the urban-scale microclimate analysis modeling method, it was determined if the heat wave damage reduction facility was effective in lowering the temperature or thermal comfort index. Cooling fog and clean roads, which are implemented on short-term scales, showed temporary temperature reduction effects using water, but also rose slightly with time delay while lowering the universal thermal comfort index UTCI. Long-term green and cool roofs have the effect of reducing the surface temperature by changing the albedo of the building’s roof surface. In the area with a cool roof, the temperature decrease was large initially, while the temperature increase was the weakest despite the increases in solar radiation and radiation during the daytime. Based on a detailed analysis of industrial complexes with the highest heat stress, the scenarios that lowered the UTCI were cooling fog, cool roofs, and urban forest creation. If these three scenarios are properly implemented in industrial complexes and surrounding areas, which are the highest heat dissipating areas in Cheongju, the urban thermal environment and energy consumption will be improved. It is expected that the results of this study will be used to increase the sensitivity of decision-making processes for installing heatwave reduction facilities and heatwave response policies.

Summer thermal comfort of pedestrians in diverse urban settings: A mobile study

Urban planning must consider the outdoor thermal comfort of city dwellers, particularly in cities where climate and the effects of climate change may severely influence human health and wellbeing in increasingly hot summers. The role of the urban forest in ameliorating this problem is decisive. The present study is based on a campaign of meteorological measurements in a large number of sites using a mobile data collection system to allow a human-centred approach. The aim is to quantify the different microclimates and thermal comfort conditions in six classes of urban morphology, discriminating landtypes with or without trees. In the case study of Florence, local physical characteristics of the sites; Sky View Factor (SVF), tree shade, ground surface cover, and canyon effect, can moderate human exposure to potentially uncomfortable thermal conditions during a typical Mediterranean summer. Significant differences in Universal Thermal Comfort Index (UTCI) were observed between treeless piazzas and streets and landtypes with trees or high height to width ratio (narrow alleys). Varying levels of SVF and tree cover in the sites allowed the construction of multivariate models, which revealed that, during common summer afternoon conditions, decreases of SVF by 12.5% or increases of tree cover by 25% can reduce the UTCI by 1°. Additionally, the total site factor, by incorporating temporally integrated sun exposure with the sky view factor, revealed itself a promising variable for future studies to use.

Borderless Heat Hazards With Bordered Impacts

AbstractHeatwaves are increasing in frequency, duration, and intensity due to climate change. They are associated with high mortality rates and cross‐sectional impacts including a reduction in crop yield and power outages. Here we demonstrate that there are large deficiencies in reporting of heatwave impacts in international disasters databases, international organization reports, and climate bulletins. We characterize the distribution of heat stress across the world focusing on August in the Northern Hemisphere, when notably heatwaves have taken place (i.e., 2003, 2010, and 2020) for the last 20 years using the ERA5‐HEAT reanalysis of the Universal Thermal Comfort Index and establish heat stress has grown larger in extent, more so during a heatwave. Comparison of heat stress against the emergency events impacts database and climate reports reveals underreporting of heatwave‐related impacts. This work suggests an internationally agreed protocol should be put in place for impact reporting by organizations and national government, facilitating implementation of preparedness measures, and early warning systems.

Forehead temperatures as an indicator of outdoor thermal comfort and the influence of tree shade

Due to climate change and a growing urban population worldwide, cities as heat islands are of increasing concern for the health and living comfort of urban populations. Accordingly, thermal comfort is an important element of bioclimatic design within cities, and areas with an abundance of hard surfaces, and a lack of tree shade, can become uncomfortably hot in summer periods, which can negatively alter usage patterns of these spaces and even become an issue of human health. In this context, a pilot study was undertaken to assess if thermal photography of the forehead of an individual can be a reliable, non-invasive, rapid tool to predict outdoor thermal comfort. A combination of street interviews, micrometeorological measurements and facial thermography was used with 775 volunteers on warm summer days in the city of Bolzano (N Italy). Two locations were chosen with contrasting sky view factors and tree shade amounts. A large difference in the mean radiant temperature, and Universal Thermal Comfort Index (UTCI), between the two locations resulted in higher thermal sensation votes and higher levels of discomfort in the space without tree shade. The mean average forehead temperature was 1.5 °C higher in the treeless space (35.2 °C) compared to the shaded space (33.7 °C). Forehead temperatures correlated significantly positively with UTCI (treeless: r = 0.30, p < 0.001; shaded: r = 0.21, p < 0.001) and air temperature (treeless: r = 0.28, p < 0.001; shaded: r = 0.22, p < 0.001). Thermal comfort was successfully predicted from forehead temperatures in the treeless space using a logistic regression model, however low R2 values limit the predictive power of these models. Facial thermography shows promise as a proxy for thermal comfort in thermally stressful spaces.

Study of Universal Thermal Comfort Index in Hosing Estate Public Space in Bangkok, Thailand

A lower external temperature increases comfort and reduces the chance of heat stress; it can be impacted by the density of the urban area, and this is an important issue for the residents in housing estate developments. Therefore, to sustainably reduce this issue, the external temperature is important to manage for urban public spaces’ development. This article reports the results of studies on increasing thermal comfort in public areas by adding different types of shading into computer programs, Rhinoceros and Grasshopper, to calculate the Universal Thermal Comfort Index (UTCI). Increasing the outdoor comfort can be done by adding shaded areas via large trees that can result in thermal reduction and humidity increase, but they do not obstruct air circulation. The result can be used as a guideline for the design of public spaces in housing estates to meet the outdoor comfort efficiently and support the users’ expectations.

Detailed investigation of vegetation effects on microclimate by means of computational fluid dynamics (CFD) in a tropical urban environment

In light of globally increasing temperatures, accentuated in cities by the urban heat island effect, urban planners and designers are looking for new, quantitative methods to assess the performance of their designs in terms of ecosystem services provided by vegetation. Among these ecosystem services, improved microclimate conditions are particularly important for human thermal comfort and health. In this study, an urban scene in the tropical city of Singapore is numerically investigated with a fully-integrated, three-dimensional urban microclimate model implemented in OpenFOAM. Mass and heat transport in air and storage effect in the urban environment are coupled so that the daily turbulent transport in air using steady Reynolds-averaged Navier-Stokes (RANS) can be solved iteratively with the unsteady heat and moisture transfer from urban surfaces. Vegetation is modeled as a porous medium for the flow of moist air and a leaf energy balance model is used to determine the heat fluxes and transpiration at leaf surfaces. The analysis shows the influence of an urban park upon air temperatures and thermal comfort. Cooling intensity of 1 °C is observed downwind of the park within a region of 27 m for an incoming wind speed of 2.3 m s−1, which reduces to 0.6 °C at a distance of 117 m from the park. The Universal Thermal Comfort Index (UTCI) shows a reduction in thermal stress in and around the park. The approach presented here can provide specific guidelines for urban planners and frame expectations on magnitude and spatial extent of local microclimate modifications generated by an urban park in a tropical city.

Unsteady-state CFD simulations on the impacts of urban geometry on outdoor thermal comfort within idealized building arrays

This study investigated outdoor thermal comfort within 5 × 5 idealized building arrays on five consecutive days by conducting unsteady computational fluid dynamic (CFD) simulations. The dynamic interacting effects of building height topology, building distance and building layout on airflow patterns, spatial distributions and spatially averaged outdoor thermal environment were evaluated by UTCI (Universal Thermal Comfort Index). CitySim Pro was used to simulate the transient solar-induced temperatures on the walls of buildings and grounds inside building arrays, which were then set as thermal boundary conditions in CFD simulations. The results showed that the influence of transient wind conditions on airflow patterns and urban thermal comfort was significant so steady simulations or unsteady simulations of one typical day might not provide a complete overview of the wind-thermal environment. The results also showed that presenting the results by average UTCI or spatial distribution could lead to different conclusions on the impacts of urban geometry on urban thermal comfort, especially the impact of building distance. Increasing the building height always provided positive effects on urban thermal comfort. The spatial distributions of UTCI in three-dimensional building arrays with equal aspect ratio diverse significantly, which was not observed in the pattern of average UTCI.

From shrubs to urban dispersion: using biomimicry to generate a comfortable outdoor microclimate in New Cairo, Egypt

ABSTRACT This study examined how urban dispersion can act as passive thermal comfort method in New Cairo, Egypt. Using shrub dispersion patterns to determine the optimum dispersion pattern for urban settlements in hot climates. Shrubs’ self-organised patterns were examined, then translated into mathematical equations that formed the basis of an algorithm to guide the redistribution of existing buildings via four proposals. These proposals were examined using the Universal Thermal Comfort Index to compare them to the existing urban dispersion patterns. The numerical and visual outcomes indicate that the proposed dispersion patterns can achieve more comfortable urban microclimate than the existing conditions.