Universal Thermal Climate Index Research Articles

Resisting the heat wave: Revealing inequalities in matching between heat exposure risk and healthcare services in a megacity

Climate warming and the growing urban heat island effect are exacerbating the unequal public health crisis in megacities, and thus it is important to assess the equity of matching relationship between the healthcare services and the heat exposure risk. We selected 255 census units in Tianjin city for the study, and calculated a heat exposure index based on the universal thermal climate index (UTCI) and constructed a comprehensive urban healthcare services evaluation system to measure the degree of mismatch between the two. The results showed the following. (1) The heat exposure risk and healthcare services followed an increasing pattern from the Outer suburb area (OSA) to the Metropolitan development area (MDA) and then to the Main urban area (MUA). (2) The overall imbalance in matching was low in the OSA, whereas the healthcare services were relatively insufficient in the MDA, and the heat exposure risk and healthcare services were relatively balanced in the MUA. (3) The degree of matching between the core and peripheral parts of the MUA was severely polarized, with an overall pattern of excess healthcare in the core area and a high risk of heat exposure in the peripheral areas. The results can provide effective guidance for rationalizing the allocation of healthcare resources from a heat exposure perspective, and provide a policy basis for risk management and fund investment.

Impact of spatial layout on vertical wind conditions and comfort levels in high-rise residential buildings in Shenzhen

Urban residential areas' rational spatial height distribution plays a crucial role in achieving a more balanced wind speed distribution, smoother air exchange, and improved space comfort. This study used Shenzhen as a representative city to analyse the effect of high-rise residential building layouts on vertical ventilation. Nine typical height-layout schemes were determined within an area of 220 × 200 m. Wind tunnel tests were conducted to validate the accuracy of the enhanced computational fluid dynamics simulations. Various parameters were comprehensively evaluated, including wind speed, wind pressure, mean age of air (MAA), and the universal thermal climate index (UTCI). The results show that different height layout schemes affect the distribution rates of wind speed, wind pressure, MAA, UTCI, and the rate of change with height. Compliance with the building row spacing specification enabled the nine schemes to obtain >83% of the windward wind speed and >48% of the leeward reasonable wind speed; the reasonable wind pressure distribution was >32% higher on the leeward side than that on the windward side. MAA statistics show that the air displacement efficiency per unit volume is generally between 120 and 300 s. >90% of the windward space in the UTCI was comfortable, and >60% of the leeward space felt slightly hot. This study shows the impact of high-rise residential layouts on comfort in hot summer and warm winter areas. It clarifies a reasonable height layout that helps realise the green liveability of residential areas.

Study of Cold Wave and Cold Stress in the Four Metropolitan Cities of India for the Period 1985–2020

Cold waves, cold nights and warm nights are major threats to human beings during winter due to climate change in different parts of India. The analysis of these has been studied for four major metropolitan cities (Chennai, Mumbai, Kolkata, and Delhi) of India during the period 1985–2020. The authors have used the 90th and 10th percentile threshold to identify the cold nights, warm nights and cold waves during the winter season. The degree of discomfort and cold stress category are identified using the Humidity Index (HD), and the Universal Thermal Climate Index (UTCI). The results indicate that the cold night event in Mumbai is ~0.36% higher than both Kolkata and Chennai cities but it is ~0.42% higher than Delhi. The number of cold wave events in Delhi is 53.5% higher than in Kolkata during the period of the study. It is also observed from the study of UTCI that the possibility of slight cold stress in the Delhi region during cold nights is 59.36% more than in other metropolitan cities. The study indicates that in the winter season, the climate of Delhi is more dynamic but for Kolkata it is relatively less dynamic.

Research on the outdoor thermal comfort of children in Hangzhou and Its influence on the underlying surface reflectance.

The outdoor thermal comfort (OTC) of children is more specific than that of adults, and the complex influence of outdoor activity spaces on children's thermal comfort warrants further investigation. To investigate the outdoor thermal comfort baseline (OTCB) of children in Hangzhou and explore the thermal impact of outdoor surfaces on children, a survey was conducted in six typical outdoor activity spaces in Hangzhou, China, during spring and summer utilizing physical measurements, questionnaire surveys, and the universal thermal climate index (UTCI). This study analyzed the differences in thermal perception among children in Hangzhou in different seasons, their OTCB, and the impact of surface reflectance (Rs) on children's OTC. The results indicated the following: 1) In spring, children in Hangzhou generally felt comfortable, but their discomfort with heat noticeably increased in summer. 2) The neutral UTCIs (NUTCIs) for Hangzhou children were 11.6°C (spring) and 27.7°C (summer), and the NUTCI ranges (NUTCIRs) were 9.7-17.5°C (spring) and 25.7-30.0°C (summer); additionally, the thermal acceptability ranges (TARs) were 13.2-25.2°C (spring) and 11.8-34.8°C (summer). 3) A high Rs made children feel more uncomfortable with heat, which was primarily due to the space's total shortwave and longwave radiation, which peaked between 14:00 and 15:00. 4) Based on the research findings, corresponding bioclimatic design strategies were proposed. Recommendations include using high Rs underlays with shading, composite underlays, or the future adoption of thermochromic coatings. Keeping permeable underlays moist is essential for activating their cooling mechanisms. Fundamental safety measures are imperative. This study provides valuable data for urban planners and landscape designers to create public spaces suitable for children's outdoor activities, contributing to a harmonious and unified living environment.

Simulation advances with EnviBatE- A case study on urban heat island mitigation in Singapore

Urban morphology and surface thermal properties are two key factors that determine the local-level urban heat island effect. Among different strategies that help in mitigating this effect, applying high reflective cool coating on urban surfaces is one of the most effective ways for changes in both the daytime and night-time urban air temperatures. In this paper, advances in the EnviBatE microclimate model for district-level numerical simulations are presented and the results are compared against full-scale experimental measurements conducted in Singapore. Key aspects of the EnviBatE tool along with their mathematical models are demonstrated. The experimental site consists of two side-by-side street canyons located at an industrial estate in the west of Singapore: one canyon with conventional and the other with cool surfaces for side-by-side comparison. The results suggest that the drop in street-level canyon air temperature varies from 1 to 4 °C with the application of the cool surface coating on roofs, walls and roads in comparison with conventional canyon under various scenarios. By analysing the effects of the three types of built-up surfaces separately, the cool roads scenario appears to have the greatest impact on canyon air temperature (at 3 m above ground), followed by the cool roofs scenario. The cool walls scenario produces negligible cooling impact. The advantages of the cool coating application on urban surfaces in reducing air temperature are statistically analysed and demonstrated. The pedestrian comfort in terms of the Universal Thermal Climate Index (UTCI) is proposed to be integrated with EnviBatE and discussed using the simulation results.

Investigating the potential of integrated urban greening strategies for reducing outdoor thermal stresses: a case of asymmetrical configuration in the tropical city of Bhopal.

In Indian cities where streets are the only affordable outdoor public space, pedestrians are always exposed to extreme heat related health risk. However, it's a challenge to reduce heat stress in existing streets characterized by asymmetrical urban configuration. Integrating vegetation without reconstituting the original orientation and geometry is one of the feasible ways to alleviate stress. Therefore, current study focuses to analyse the heat stress reduction potential of urban greenery strategy in asymmetrical urban configuration from spatiotemporal perspective. It initiates with the selection of commercial streets in extreme hot climate with an on-site measurement of its climatic and morphological attributes. Furthermore, it leads to the classification and prioritizing of street's sections linked to hot-spots determined by varied sky view factor and asymmetrical aspect ratio. Finally, an Envi-Met model with iterated scenarios at the building and street levels is developed, incorporating three strategies (trees, grass, green-walls). The impact of heat related health risk is quantified using a thermal index Universal Thermal Climate Index along with air temperature and mean radiant temperature. The results suggested that due to asymmetricity a fixed strategy would not be applicable across the street. The highest reduction was observed by trees in asymmetrical sections while lowest was recorded by green-wall. However, it would be worthwhile to adopt green-wall along with dense tree's (leaf area density, 0.3) in order to reduce the heat stress in deeper sections. The evidence-based integration of Urban greenery can assist planners and designers in mitigating extreme heat stress in similar complex urban environment.

Analysis of the summer thermal comfort indices in İstanbul.

Thermal indices and thermal comfort maps have great importance in developing health-minded climate action strategies and livable urban layouts. Especially in cities where vulnerability to heatwaves is high, it is necessary to detect the most appropriate indicators for the regional characteristics and action planning with respect to thermal comfort. The aim of the study is to examine thermal indices as indicators of regional climate characteristics by relating to meteorological parameters and spatial features. Atmospheric variables including air temperature, wind speed, cloud cover, and relative humidity data were obtained from 30 meteorological stations located in districts having different climatic features. Heat stress levels for apparent temperature (AT), heat index (HI), wet bulb globe temperature (WBGT), physiological equivalent temperature (PET), universal thermal climate index (UTCI), and perceived temperature (PT) indices were calculated and associated with meteorological parameters. Thermal comfort maps have been created with the daily mean and maximum values of all indices. As a result, the meteorological parameters with the strongest correlation with all thermal indices are air temperature (Ta) with r = 0.89 ± 0.01 and mean radiant temperature (Tmrt) with r = 0.75 ± 0.16. The differences in thermal stress levels over the city have been distinctively observed in the ATmax, PETmax, and PTmax maps, which are generated by the daily maximum values of the indices. Çatalca, where forests cover large areas compared to highly urbanized districts, has the lowest heat stress defined by all indices.

Summer cooling island effects of blue-green spaces in severe cold regions: A case study of harbin, China

Blue-green spaces exhibit a cooling island effect in urban thermal environments. This study, through field measurements combined with thermal comfort indices and CFD simulations, explored the summer cooling island effect in micro-scale blue-green spaces of severe cold regions, summarizing the spatiotemporal characteristics of the effect. Measurements were conducted in Harbin at three water bodies of varying sizes and shapes, revealing a notable cooling island effect at a distance of 6–8 m from the water. The highest Mean Cooling Island Intensity (MCII) of 3.18 °C was recorded at 10 a.m. in a circular water body with compound vegetation. Furthermore, the combination of water bodies and vegetation proved more effective in reducing temperatures than single factors alone, with the peak coupling effect of 6.37 °C at 6 m from the water at 11 a.m. Thermal environment surveys determined Harbin's Neutral Universal Thermal Climate Index (UTCI) temperature range to be 13.3–25.06 °C. Additionally, modeling and optimization comparisons in ENVI-met confirmed that adding a small number of deciduous trees to grassland areas and altering the type of waterside platform can optimize the thermal environment. This research provides a solid foundation for the optimized design of blue-green spaces in severe cold regions.

Investigating urban canyons, façade albedo, and pedestrian thermal comfort using microclimate model calculations

Previous studies have shown a strong relationship between heat-related fatalities and ambient air temperature. This problem is expected to increase due to constant urbanization and the threat of global warming. Therefore, designing urban street canyons (USC) to be thermally comfortable is essential for a healthy urban life. This paper investigates the correlation between an urban street canyon’s aspect ratio and the albedo material of its surrounding buildings. The aim is to study which combination can successfully mitigate urban heat stress and create a thermally comfortable pedestrian microclimate. This research uses a comparative analysis that suggests the optimum albedo for different USC geometries. An ENVI-met model was used to simulate 9 scenarios for an idealized 2D USC with varying aspect ratios and albedo values. Air temperature, mean radiant temperature and Universal Thermal Climate Index (UTCI) were analyzed. Results show that a medium albedo value performs best thermally in all USCs. High albedo had 13.2% more combined thermal stress compared to medium albedo. However, high albedo performed much better in deep canyons than wider ones, with the average UTCI decreasing by about 4.8%-5.7% when used in deep canyons. Medium albedo should be exclusively used in wide canyons for minimal thermal stress. Practical application: This study provides a reference to the use of materials in urban street canyons of different aspect ratios to achieve good outdoor thermal comfort for pedestrians.

Региональные особенности динамики показателей теплового комфорта на фоне изменения климата

The regional changes in climate comfort for the territories located in different climate zones are analyzed. The Universal Thermal Climate Index (UTCI) is used to assess bioclimatic conditions. The eight-time observation data on the following parameters from six Roshydromet weather stations were used for calculations: air temperature, wind speed, relative humidity, soil surface temperature, and cloudiness for 56 years from 1966 to 2021. It was found that climate change and its impact on human comfort in different climate zones occur at different rates. For all territories, cold stress decreases in the cold season, and heat stress increases in the warm season. It is noted that the average annual total number of extremely discomfort days has decreased over 56 years. The main factor determining the revealed dynamics of UTCI and characteristic for cities both in the continental part of Russian Federation and on the coast of the oceans is the air temperature rise in winter and summer and the wind speed decrease in winter.

Heat stress resilience assessment of urban form from physical space dimension: A case study of Guangdong-Hong Kong-Macao Greater Bay Area

Improving urban resilience is crucial to counteract rising high-temperature disasters. This study constructed a framework for a process-based heat stress resilience (HSR_phy) assessment from the urban physical space dimension. Based on the universal thermal climate index (UTCI), the Weather Research and Forecasting (WRF) model, and the Local Climate Zone (LCZ) map generated through WUDAPT, an HSR_phy evaluation method with high spatiotemporal accuracy is proposed. The Guangdong-Hong Kong-Macao Greater Bay Area (GBA) was studied for heat stress resilience patterns in July 2021. Boosted regression tree (BRT) models analyzed LCZ landscape patterns' impacts on HSR_phy. The results indicated that HSR_phy during the daytime was significantly lower than that at night. The HSR_phy of GBA showed the characteristics of low inland and high periphery. Significant differences in HSR_phy existed among most LCZs. LCZA, LCZC, and LCZ9 showed strong HSR_phy, whereas LCZ2, LCZ8, and LCZ7 were opposite. At the 1500 m scale, the Percentage of Landscape (PLAND), Landscape Shape Index (LSI), and Shannon's Diversity Index (SHDI) of LCZ4, LCZ5, and LCZ6 were the key factors affecting HSR_phy. Our research demonstrates how to quantify heat stress resilience and impact factors of urban physical spaces to provide a basis for developing climate-sensitive urban design strategies.

Impacts of Photovoltaic Façades on the Urban Thermal Microclimate and Outdoor Thermal Comfort: Simulation-Based Analysis

Cities face the consequences of climate change, specifically the urban heat island (UHI) effect, which detrimentally affects human health. In this regard, deploying PV modules in urban locales prompts inquiry into the impact of energy-active building components on the adjacent thermal microclimate and human thermal comfort. A twofold simulation-based methodology addresses this subject: First, the implications of façade-integrated photovoltaics on the urban thermal microclimate are investigated using a case study in Munich, Germany. Secondly, a parameter study allows us to gain further insights into the relevance of several parameters on the microthermal impact. The simulation results show a daytime heating effect of photovoltaics on the mean radiant temperature of up to +5.47 K in summer and +6.72 K in winter. The increased mean radiant temperature leads to an elevation of the Universal Thermal Climate Index of up to +1.46 K in summer and +2.21 K in winter. During night-time, no increase in both metrics is identified—hence, nocturnal recovery as a key element for human health is not affected. Despite extended human exposure to thermal heat stress in summer, PV façades improve the annual outdoor thermal comfort autonomy by 0.91% due to lower cold stress in winter. The higher PV efficiencies and lower albedo of the reference building surface lower the heating effect. However, with the current efficiencies, PV façades consistently lead to heating of the surrounding thermal microclimate in summer and lower the outdoor thermal comfort.

Comparison of cooling grey solutions in the sense-city urban demonstrator for adapting cities to heat waves

SummaryFaced with the increase in urban heat in summer, cities must quickly adapt by offering cool islands. If nature-based solutions are efficient and popular, other so-called grey solutions exist and can also provide solutions. In this paper we compare standard grey solutions in Sense-city, an urban demonstrator equipped with sensor, located in the scientific campus of Cité Descartes at Marne la Vallée. Our objective is on the one hand to compare the effectiveness of standard solutions over time, but also to study the ability of sense-city and its canyon street to study this phenomenon despite its relatively small size. MethodsIn this work we follow an experimental approach using a wide coverage of calibrated sensors deployed in Sense-city. We have conducted two measurement campaigns in July 2021 and July–August 2022 where we study the effectiveness of standard solutions (shading, white floor surface, street watering) to reduce the air temperature in the canyon street of sense-city. As the days are different, we compare the temperature difference in the street canyon equipped with these cooling solutions with that on the surrounding area. This method allows us to overcome daily variations. To interpret the results, we analyse the shades and we follow the temperature over time and not only during the hottest hours. We also calculate the UTCI (Universal Thermal Climate Index) to compare the perceived temperature. FindingsThe results show that despite its small size, the canyon street of sense-city behaves like a canyon street and that the measured temperature differences due to heat exchanges comply with physical laws and that the number and spatial distribution of sensors is validated. The Sense-city demonstrator can therefore be used to carry out thermal efficiency experiments. In addition, the method we used to compare cooling solutions allows us to limit the impacts due to slight daily variations. Finally, while watering is effective in rapidly lowering the temperature in the street, shading remains an optimal solution for the perceived temperature, even if it would be ideal to close them at the end of the day to allow air circulation.

The effects of extreme heat on human health in tropical Africa.

This review examines high-quality research evidence that synthesises the effects of extreme heat on human health in tropical Africa. Web of Science (WoS) was used to identify research articles on the effects extreme heat, humidity, Wet-bulb Globe Temperature (WBGT), apparent temperature, wind, Heat Index, Humidex, Universal Thermal Climate Index (UTCI), heatwave, high temperature and hot climate on human health, human comfort, heat stress, heat rashes, and heat-related morbidity and mortality. A total of 5, 735 articles were initially identified, which were reduced to 100 based on a set of inclusion and exclusion criteria. The review discovered that temperatures up to 60°C have been recorded in the region and that extreme heat has many adverse effects on human health, such as worsening mental health in low-income adults, increasing the likelihood of miscarriage, and adverse effects on well-being and safety, psychological behaviour, efficiency, and social comfort of outdoor workers who spend long hours performing manual labour. Extreme heat raises the risk of death from heat-related disease, necessitating preventative measures such as adaptation methods to mitigate the adverse effects on vulnerable populations during hot weather. This study highlights the social inequalities in heat exposure and adverse health outcomes.

Natural shading vs. artificial shading: A comparative analysis of their cooling efficacy in extreme hot weather

Shading, comprising both natural and artificial coverings, is an efficient and effective strategy to reduce heat stress in outdoor environments. Despite its recognized efficiency, there is limited comparative insight into the cooling performance of natural and artificial shading. This study examined the cooling efficacy of two covered walkways and two tree canopies, concerning microclimate conditions by various variables and thermal stress quantified by four thermal indices. Our findings highlight three key points: Firstly, the average cooling effects provided by natural and artificial shading were comparable, including reductions in air temperature (1.42 °C vs. 1.31 °C), mean radiant temperature (15.93 °C vs. 13.71 °C), and Physiological Equivalent Temperature (PET) (9.06 °C vs. 9.70 °C), Universal Thermal Climate Index (UTCI) (4.71 °C vs. 5.08 °C), and Hong Kong Heat Index (HKHI) (2.36 °C vs. 2.50 °C). Secondly, it is inconsistent which shading solution is better for microclimate improvement and heat stress alleviation, which is affected by canopy materials, configurations, and tree species. Thirdly, the four indices presented an inconsistent pattern in heat stress assessment. Notably, PET and UTCI showed similar patterns, while HKHI and modified PET presented lower sensitivity to high heat stress. This study offers valuable insights for urban designers to create sustainable shaded communities and also initiates a discourse for revising local heat warning systems, considering various thermal stress indices.

Factors influencing outdoor thermal comfort in a coastal park during the transition seasons in cold regions of China

Coastal outdoor spaces serve as public venues where individuals engage in water-related activities, admire scenic views, embark on tourist excursions, and partake in social gatherings. Enhancing thermal comfort is a crucial prerequisite for increasing the attractiveness of these spaces. This study investigated the outdoor thermal comfort (OTC) in a coastal park called Xinghai Park located in a cold region of China over a period of five days during the spring and autumn seasons. The universal thermal climate index (UTCI) was employed to establish the thermal benchmark. Through on-site measurements and questionnaire surveys, both single-factor and multi-factor analyses were conducted to assess the microclimate and thermal perception in four representative coastal spaces, thereby identifying the thermal benchmark and factors influencing thermal perception in the Coastal Park. The findings indicated that: (1) during the transition seasons, the neutral UTCI (NUTCI) of the Coastal Park was 15.3 °C, with neutral UTCI range (NUTCIR) ranging from 9.3 °C to 21.4 °C, and there were significant variations in the thermal benchmarks among different types of spaces; (2) the primary factors influencing thermal perception during the transition seasons in the Coastal Park were physical factors (Ta, Tg, RH, Va, G), while individual, social, and psychological factors also exerted varying degrees of influence on respondents' thermal perception; (3) there were substantial spatial differences in the factors influencing respondents' thermal perception. The findings of this study provide valuable references for determining thermal environmental design strategies for transitional season coastal outdoor recreational spaces and enhancing the quality of urban life.

A Community Information Model and Wind Environment Parametric Simulation System for Old Urban Area Microclimate Optimization: A Case Study of Dongshi Town, China

In the context of an increasingly extreme climate, Urban Heat Island (UHI) mitigation of communities through ventilation has recently attracted more attention. To explore the impact mechanisms of different morphological renovation schemes on its wind and thermal environment, this paper selected the Laozheng Community as a case study and: (1) analyzed measured data to quantitatively investigate the UHI within the community; (2) established the CIM-WTEPS system to construct community information models and to conduct wind environment parametric simulation for seven micro-renovation schemes across three levels; (3) performed correlation analyses between morphology indicators and wind environment indicators; (4) conducted the thermal environment parametric simulation of the community under different schemes. The results reveal that: (1) the Laozheng Community exhibits the Urban Heat Island Intensity (UHII) of up to 6 °C; (2) apart from the “ Hollowing “ scheme, which deteriorates the community wind environment, all other schemes optimize it, potentially increasing the average wind speed by up to 0.03m/s and in the renovated area by up to 0.42 m/s; (3) building density is highly correlated with the average wind speed and the proportion of calm wind area, with correlation coefficients of −0.916 (p < 0.01) and 0.894 (p < 0.01), respectively; (4) the adding of shading facilities can enhance the proportion of areas with lower Universal Thermal Climate Index (UTCI) without adversely affecting the optimization effects of the wind environment, achieving an maximum increase of 3.1%. This study provides a reference for optimizing the community’s microclimate through morphological micro-renovations and detailed operations, aiding designers in better controlling community morphology for in future community renewal and design planning, thereby creating a more hospitable outdoor environment.

Effects of outdoor activity intensities on college students’ indoor thermal perception and cognitive performance

Using neurobehavioral tests, electroencephalogram signal monitoring, and questionnaire surveys, we recruited 158 healthy college students to explore the effects of light, moderate, and vigorous intensity activities on indoor thermal perception, cognitive performance, physical health and emotions in a hot outdoor environment. Our results suggested four principal outcomes: (1) compared with the pre-exercise, reduction in mean thermal sensation gradually increased while reduction in mean thermal comfort decreased as the proportion of thermal symptoms increased by 17.0%, 48.0%, and 76.0% during light to vigorous activity; (2) when the Universal Thermal Climate Index changed between 23.0 °C and 49.2 °C, moderate intensity activity can maximize the cognitive performance of college students indoors; (3) the skin temperature measured at the upper arm increased at higher intensity activity. Systolic pressure, diastolic pressure, and eardrum temperature significantly increased after engaging in different intensity activities. Heart rate showed a significant increase after moderate to vigorous intensity, while oxyhemoglobin saturation decreased following vigorous intensity; and (4) when returning indoors after engaging in outdoor activities, frontal brain asymmetry increased by 0.17 as positive emotions enhanced; but after vigorous intensity, the frontal lobe asymmetry decreased by 0.11 as negative emotions increased. Our results could provide fundamental guidance to improve the indoor learning efficiency and thermal comfort of college students.

Improving the operational forecasts of outdoor Universal Thermal Climate Index with post-processing

The Universal Thermal Climate Index (UTCI) is a thermal comfort index that describes how the human body experiences ambient conditions. It has units of temperature and considers physiological aspects of the human body. It takes into account the effect of air temperature, humidity, wind, radiation, and clothes. It is increasingly used in many countries as a measure of thermal comfort for outdoor conditions, and its value is calculated as part of the operational meteorological forecast. At the same time, forecasts of outdoor UTCI tend to have a relatively large error caused by the error of meteorological forecasts. In Slovenia, there is a relatively dense network of meteorological stations. Crucially, at these stations, global solar radiation measurements are performed continuously, which makes estimating the actual value of the UTCI more accurate compared to the situation where no radiation measurements are available. We used seven years of measurements in hourly resolution from 42 stations to first verify the operational UTCI forecast for the first forecast day and, secondly, to try to improve the forecast via post-processing. We used two machine-learning methods, linear regression, and neural networks. Both methods have successfully reduced the error in the operational UTCI forecasts. Both methods reduced the daily mean error from about 2.6∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{\\circ }$$\\end{document}C to almost zero, while the daily mean absolute error decreased from 5∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{\\circ }$$\\end{document}C to 3∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{\\circ }$$\\end{document}C for the neural network and 3.5∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{\\circ }$$\\end{document}C for linear regression. Both methods, especially the neural network, also substantially reduced the dependence of the error on the time of the day.

High-resolution projections of outdoor thermal stress in the twenty-first century: a Tasmanian case study

To adapt to Earth’s rapidly changing climate, detailed modelling of thermal stress is needed. Dangerous stress levels are becoming more frequent, longer, and more severe. While traditional measurements of thermal stress have focused on air temperature and humidity, modern measures including radiation and wind speed are becoming widespread. However, projecting such indices has presented a challenging problem, due to the need for appropriate bias correction of multiple variables that vary on hourly timescales. In this paper, we aim to provide a detailed understanding of changing thermal stress patterns incorporating modern measurements, bias correction techniques, and hourly projections to assess the impact of climate change on thermal stress at human scales. To achieve these aims, we conduct a case study of projected thermal stress in central Hobart, Australia for 2040–2059, compared to the historical period 1990–2005. We present the first hourly metre-scale projections of thermal stress driven by multivariate bias-corrected data. We bias correct four variables from six dynamically downscaled General Circulation Models. These outputs drive the Solar and LongWave Environmental Irradiance Geometry model at metre scale, calculating mean radiant temperature and the Universal Thermal Climate Index. We demonstrate that multivariate bias correction can correct means on multiple time scales while accurately preserving mean seasonal trends. Changes in mean air temperature and UTCI by hour of the day and month of the year reveal diurnal and annual patterns in both temporal trends and model agreement. We present plots of future median stress values in the context of historical percentiles, revealing trends and patterns not evident in mean data. Our modelling illustrates a future Hobart that experiences higher and more consistent numbers of hours of heat stress arriving earlier in the year and extending further throughout the day.