Strong Heat Stress Research Articles

Unexpectedly strong heat stress induction of monoterpene, methylbutenol, and other volatile emissions for conifers in the cypress family (Cupressaceae)

We investigated the biogenic volatile organic compound (BVOC) emission rates and composition of Cupressaceae species and how the emissions change in response to moderate warming and more severe heat stress. A total of 8 species from 7 distinct Cupressaceae genera were targeted in this study and exposed to laboratory-simulated heatwaves. Each plant was enclosed in a temperature-controlled glass chamber and allowed to equilibrate at 30 °C for 24 h. The temperature was then increased stepwise from 33 °C to 43 °C in 2 °C increments, with each step lasting 2 h, and was finally kept at 45 °C for 12 h. The BVOC emissions were measured periodically using an automated air sampler coupled to a gas chromatograph.Most of the sampled Cupressaceae species (6 out of 8) were low BVOC emitters (<0.3 μgC g−1 h−1) at 30 °C. However, the BVOC emissions of all 8 species increased strongly with temperature, and in most species (5 out of 8), the emissions continued to increase with longer exposure times to heat stress. The largest increase was observed in Thuja occidentalis and Chamaecyparis thyoides, which reached maximum emissions of 350 and 190 μgC g−1 h−1, respectively. Of the different BVOCs, monoterpenes responded most strongly to heat stress, with Q10 temperature coefficients typically ranging between 7.6 and 22, which were significantly greater than the model-predicted value of 2.7. Other BVOCs including sesquiterpenes, C9 aromatics (only detected in Calocedrus decurrens), methylbutenols, and other C5 oxygenates were also induced by heat stress, but generally at a lower magnitude than monoterpenes.Our results indicate that Cupressaceae are a large but typically dormant source of reactive volatile hydrocarbons (mostly monoterpenes) whose emissions can be activated by heat stress. This phenomenon could have important implications for ozone and aerosol formation, air quality, and human health, particularly in urban areas that are prone to heatwaves.

Intensification of thermal risk in a changing climate: findings from prominent tourism destinations along the eastern Adriatic coast.

The climate and thermal comfort of а destination greatly influence the tourism industry. Therefore, this study was focused on researching thermal comfort changes and their impacts on visitors in four highly visited coastal destinations along the eastern Adriatic coast (Pula, Zadar, Split, and Dubrovnik) from 1996 to 2020, using the modified physiologically equivalent temperature index (mPET). The specific objective was to assess how the thermal comfort conditions are distributed spatially and temporally and how they are suitable for beach and sightseeing tourism. Results showed that monthly mean mPET values have increased, except in May. In the summer season, tourists were often exposed to uncomfortable heat stress, especially in the middle of the day. Strong and extreme heat stress frequency significantly increased in all sites except in Pula, particularly in July and August. Prevailing neutral and slightly warm/cold conditions were concentrated in two periods, between April and June and in September and October. The maximum occurrence of optimal climatic conditions for enjoying the beach was in the summer, with a decreasing tendency from May to August. The occurrence of favorable conditions for sightseeing significantly increased in April and November while it decreased from July to September. Although the eastern Adriatic coast is primarily a summer tourist area, a relatively small number of tourists take advantage of the period with optimal thermal comfort. Despite the fact that the number of tourists in the shoulder seasons has increased significantly in the past 25 years, the increasing favorable thermal comfort in the changing climate conditions will make these seasons even more appealing in the future, especially for sightseeing activities. New strategies for adapting to a changing climate are therefore needed.

Association between physiological responses and heat shock protein 70 (HSP70) expressions in the vulnerable populations of Kuala Lumpur

ABSTRACT Continued heat exposure can cause physiological and cellular responses. This study investigated the association between physiological responses and heat shock protein 70 (HSP70) expressions in Kuala Lumpur’s urban vulnerable population. We conducted a cross-sectional study involving 54 participants from four areas classified as experiencing moderate to strong heat stress. Physiological measurements included core body temperature, heart rate, and diastolic and systolic blood pressure. RT-qPCR and ELISA were also performed on blood samples to assess HSP70 gene and protein expressions. Despite indoor heat stress, participants maintained normal physiological parameters while there were significant indications of HSP70 expression at both the gene and protein levels. However, our study found no significant correlation (p > 0.05) between physiological responses and HSP70 expressions. This study shows no interaction between physiological responses and HSP70 expressions in the study population, revealing the complex mechanisms of indoor heat stress in vulnerable individuals.

Exploring the effects of landscape interventions on outdoor thermal comfort using digital simulation

Abstract The assessment of outdoor thermal comfort plays an important role in design decisions and encourages better planning and development of outdoor environments. This study explores the potential effects of landscape interventions on outdoor thermal comfort, testing two thermal comfort indicators on a selected hospitality development. Results are crucial factors to consider as the success of hospitality developments and its outdoor spaces are dependent on how visitors perceive and interact with them. Digital simulations were conducted using Rhinoceros software and the Grasshopper tool to produce heat maps. For the purpose of the study, two sets of simulations were developed to examine changes in the Universal Thermal Climate Index (UTCI) and Incident Radiation of the site – a) buildings alone and b) with landscape elements. As a result, UTCI with landscape intervention decreased by 2°C while Incident Radiation is significantly lower throughout spaces provided with shading elements. Results of UTCI simulations still deliver strong heat stress to occupants, while Incident Radiation has considerably improved with landscape interventions. The provision of shading elements helped lessen solar radiation penetrating the site, thus improving the thermal comfort of users. Wind velocity showed minimal effects on perceived heat based on the UTCI assessment scale. Nonetheless, improvement in the planning and orientation of buildings and strategic provision of demountable sun shading elements in future developments are recommended to allow better air circulation.

Spatiotemproal changes and hot spots of UTCI index over Iran

In this study, the Universal Thermal Climate Index (UTCI) gridded data from ECMWF (European Centre for Medium-Range Weather Forecasts) database was applied to assess the spatiotemproal changes in thermal comfort in Iran for 1990–2021. This index's monthly changes and trends have been determined, using the Mann-Kendall nonparametric test. Moran's I was used to compute the index's spatial autocorrelation, and the Getis-Ord Gi* statistic was used to calculate the index's hot and cold spots. The findings indicated that the majority of the country experiences thermal comfort condition from June to October. Furthermore, no location of Iran has recorded very hot or very strong heat stress. Moderate and strong heat stress has only been recorded in a few areas along the southern coasts from May to November. Most of the country experiences strong, moderate, or slight cold stress from January to May, as well as November and December. According to the Moran I autocorrelation index, the spatial pattern of UTCI in Iran is cluster throughout the year. Significant hot spots have also formed throughout the country's southern coasts, with limited spatiotemproal variability. Significant cold spots have also formed, with more temporal and spatial variability, along the Alborz and Zagros mountain ranges.

On the impact of climate change on urban microclimate, thermal comfort, and human health: Multiscale numerical simulations

Climate change is expected to aggravate urban microclimatic conditions and have adverse effects on human morbidity and mortality. However, there is limited knowledge on the impact of climate change on urban microclimate and human health for actual urban areas. In this study, we investigate the impact of climate change on urban microclimate and pedestrian thermal comfort within a complex district in Nicosia, Cyprus. Two climatic scenarios are considered: (i) current scenario based on meteorological conditions derived from field measurements performed in 2010, and (ii) future scenario for which meteorological conditions of 2050 are based on downscaled Regional Climate Models (RCMs). URANS CFD simulations are performed for the period of 9–10 July with a 1-h time-step. The results show that by 2050, the maximum air temperature at the pedestrian height of the case study area can increase by 2.3 °C which can increase heat-related mortality by more than 240 %. The UTCI is expected to significantly increase especially in the afternoon hours with up to a 4.3 °C increase at 20:00. The “very strong heat stress” conditions (UTCI: 38–46 °C) are expected to prevail for a longer period during the day, increasing from 3.3 to 6.6 h. In addition, the “extreme heat stress” conditions (UTCI: >46 °C) are expected to apply in parts of the area. This prolonged exposure to heat stress can incite additional health risks.

Climate walking and linear mixed model statistics for the seasonal outdoor thermophysiological comfort assessment in Lisbon

To measure urban outdoor pedestrian thermophysiological comfort mobile roving missions were conducted in all seasons of the year during the day and at night. Six routes were chosen, representing areas of the city with varying urban morphological layouts. The thermal comfort conditions were analysed using the Local Climate Zone spatial scale. This enabled the identification of typologies of areas where pedestrians might feel (un)comfortable. To achieve the proposed objectives, quantitative and qualitative analysis were run, namely a Linear Mixed-Effect Model. This model was useful to understand the thermal behaviour of the roved areas by comparison to a reference area. The city was found to be generally cooler, except at night when it can have a 44% increased UTCI. Most collected values throughout the year had ‘no thermal stress’, except in the summer when ‘moderate’ and ‘strong heat stress’ was predominant. Compact and large low rise urban areas were found to be the most uncomfortable. Significant amplitudes were found in some LCZs, reaching as high as 7 °C in some scenarios. Sparsely wooded areas exhibited higher values in all seasons and at night, except in the summer. This showed that for a local heat stress analysis a higher resolution scale is needed.

Vulnerability Assessment of a Highly Populated Megacity to Ambient Thermal Stress

The urban ambient environment is directly responsible for the health conditions of millions of people. Comfortable living space is a significant aspect that urban policymakers need to address for sustainable planning. There is still a notable lack of studies that link the spatial profile of urban climate with city-specific built-up settings while assessing the vulnerability of the city population. Geospatial approaches can be beneficial in evaluating patterns of thermal discomfort and strategizing its mitigation. This study attempts to provide a thorough remote sensing framework to analyze the summer magnitude of thermal discomfort for a city in a tropical hot and humid climate. Spatial profiles of dry bulb temperature, wet bulb temperature and relative humidity were prepared for this purpose. A simultaneous assessment of various discomfort indices indicated the presence of moderate to strong heat stress to a vast extent within the study area. The central business district (CBD) of the city indicated a ‘danger’ level of heat disorder for outdoor exposure cases. Nearly 0.69 million people were vulnerable to a moderate threat from humid heat stress, and around 0.21 million citizens faced strong heat stress. Combing city morphology in the study showed that mid-rise buildings had the maximum contribution in terms of thermal discomfort. City areas with built-up cover of more than 68%, along with building height between 5.8 m and 9.3 m, created the worst outdoor discomfort situations. Better land management prospects were also investigated through a multicriteria approach using morphological settlement zones, wind direction, pavement watering, building regulations and future landscaping plans. East–west-aligned road segments of a total 38.44 km length were delineated for water spray cooling and greener pavements. This study is likely to provide solutions for enhancing ambient urban health.

Ambient temperature modelling from surface characteristics and associating urban morphology with thermal discomfort

Urban heat island assessment is of paramount importance when monitoring microclimate changes, increased heat stress, mortality and energy consumption. Simply analysing land surface temperature patterns for human comfort and health assessment is often inadequate. In this study, we attempt to resolve this inadequacy with ambient temperature modelling from multiple surface characteristics for a tropical megacity. A 336 datapoint‐based multilinear regression model was formulated to predict the maximum summer air temperature with a mean absolute error of 0.694°C. Specific locations of critical thermal environments were demarcated with Getis‐Ord statistic. Based on our results, extreme hotspots covered 10.53 per cent of the city on a daily basis at 99 per cent confidence level. The application of an outdoor thermal comfort index highlighted the existence of very strong heat stress zones over 14.67 per cent of the study area. The air temperature hotspots were verified with intra‐urban variation in carbon sequestration. This environmental parameter was used to strengthen the observed results since, carbon sequestration directly links urbanization with degradation of thermal environments. Further, five urban morphological parameters were analysed to conclude that building density and height were the most significant urban design factors leading to increased air temperature. Simultaneous local climate zone mapping depicted that heat islands were dominated by mid and high‐rise built‐up areas, of which 68.44 km2 of that area is suitable for vertical and roof gardening. Another 33.29 km of road stretch was delineated within low‐rise built‐up areas with scope for green landscaping to improve urban sustainability.

Thermal stress and comfort assessment in urban areas using Copernicus Climate Change Service Era 5 reanalysis and collected microclimatic data

In this initial study of a research project, this paper seeks to understand the thermal conditions in the cities of Lisbon and Munich, specifically focusing on Urban Heat Island intensity and on thermal comfort using the Universal Thermal Climate Index modeling data at the Local Climate Zone scale. Based on these datasets, Munich has exhibited more unfavourable thermal conditions than Lisbon. In terms of UHII, both cities have shown that low, medium, and high rise compact urban areas and bare rock or paved areas have the highest values, while sparsely built areas have the lowest. These results differ from the UTCI, which indicates that in Lisbon and Munich, these sparsely built areas as well as areas with low plants and vegetation are the most uncomfortable. In Munich, the population was exposed to very strong heat stress, while Lisbon experienced strong heat stress conditions. Conversely, low, medium, and high rise compact urban areas and densely wooded areas in Munich, and scattered trees areas and large low-rise urban areas in Lisbon, have demonstrated the lowest monthly mean and average maximum values. These results will be further explored in future studies in the city of Lisbon and cross-checked with data obtained from roving missions. This will enable a more detailed temporal and local analysis.

Urban tree canopies drive human heat stress mitigation

Climate warming and urbanisation compound the public health risk posed by heat. Heat can be mitigated at local scales through urban greening, which provides shade and reduces surface and air temperatures. Yet, the relative effectiveness of different greening options on human thermal comfort based on physiology-based indices is understudied. We installed microclimate stations at 17 locations covering a gradient of tree canopy cover and perviousness in the city of Ghent, Belgium, and monitored the modified Physiologically Equivalent Temperature (mPET) during 195 days over Spring and Summer. We assessed the canopy cover, pervious surface fraction and building sky fraction based on field measures and hemispherical pictures. Unpaved locations with trees experienced a 2.4-fold reduction in the number of days with strong heat stress (mPET > 35 °C) compared to paved, treeless locations. Based on mixed models and our selected environmental variables, cooling effects were predominantly driven by tree canopy cover, where locations with 100% canopy cover had temperature maxima 5.5 °C mPET lower than treeless locations throughout the monitoring period. When air temperatures rose to 40 °C, cooling by tree canopies increased to 8.8 °C mPET. The pervious surface fraction and building view factor were less influential, generating variation of at most 1.7 °C and 1.1 °C mPET, respectively. In contrast, night-time temperatures were rather determined by the regional-scale urban heat island effect than by aforementioned local factors. Still, tree canopies slightly cooled the warmest nights only, whereas the vicinity of buildings led up to 1.2 °C mPET warming on average. Expanding the urban tree cover may therefore be the best solution for improving local thermal comfort levels when daytime heat peaks, but will provide little relief at night.

A hybrid Python approach to assess microscale human thermal stress in urban environments

Microclimate simulations are in high demand to assess the thermal impacts of urban design and vegetation changes. Modeling accurate microclimate dynamics in complex urban settings requires extensive computing power. A hybrid Python approach is introduced to simulate human thermal exposure (mean radiant temperature, MRT) and comfort (Universal Thermal Climate Index, UTCI) in cities. The proposed model combines various engines in Rhinoceros to account for interactions between urban surfaces, tree canopies, and the atmosphere. The model was validated in hot, dry Tempe, USA, using in-situ human-biometeorological observations and then applied to urban archetypes in Bologna and Imola, Italy. MRT and UTCI were simulated at five sites in Bologna, four in Imola, and four in Tempe, with varying building heights and canopy cover for the climatologically hottest week of the year (August 3–9). The model performed well with an RMSE of 5.4 °C, an index of agreement of 0.96, and outperformed existing models for tree-shaded sites. MRT and UTCI were driven mainly by shade from dense urban forms and trees. Highrise, medium-to-high tree canopy cover archetypes were the coolest concerning thermal exposure and comfort. Sites in Tempe exceeded the UTCI categories for Very Strong or Extreme Heat Stress independent of archetype. The model enables fast and accurate assessment of urban tree planting strategies.

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.

A 43-year of human thermal comfort in Central Africa.

In this study, the human thermal stress was quantified across Central Africa (C.A.) using the Universal Thermal Climate Index (UTCI). Although many of the documented studies on the use of UTCI in relation to human health are currently restricted to countries in the northern hemisphere, this contribution constitutes a prerequisite of information for future research in the region. To mitigate the problem of lack of field data in the Central African sub-region, we downloaded UTCI data via the ERA5 reanalysis portal. Based on this data source, we have explored the spatiotemporal characteristics and the resulting behaviour at annual, seasonal and monthly scales in Central Africa over the period 1982 to 2022. On these different scales, 4 of the 10 UTCI thermal stress categories were experienced, ranging from mild cold stress to strong heat stress. Spatially, cases of moderate heat stress were the most widespread, with cases of strong intensity occurring in a few isolated areas in the centre, east and west. Slight cold stress is confined to the south-east domain, particularly in autumn and winter. From 1982 to 2022, heat stress has increased significantly in the region, with peaks observed in January and October; very few areas have been spared the phenomenon of thermal stress. However, a slight decreasing trend was noticed along coastal regions and the south of C.A. Thereafter, the trend values showed the degree of C.A. vulnerability to global warming, and thus appropriate measures should be taken in relation to outdoor occupations and its impacts on the population of this region.

Heat stress in South America over the last four decades: a bioclimatic analysis

The observed continuous rise in the frequency of extreme heat events in South America (SA) poses a serious challenge for public health. However, there is a lack on the understanding of the large-scale and long-term variability and trends of thermal stress in this continent. Accordingly, here we developed the first comprehensive bioclimatology of thermal stress over SA during the past four decades. Consecutive heat stress hours were analyzed using the Universal Thermal Climate Index (UTCI) from ERA5-HEAT reanalysis according to the Köppen–Geiger climate classification and also focusing on the 31 most populated cities of SA. Results show an inland/coastline contrast and a marked latitudinal northward increase in the number of hours under heat stress. Heat stress hotspots are located mostly around the Amazon, northern and central parts of SA with 26–35% of the hours between 1979 and 2020 under strong heat stress. The annual number of hours within heat stress increased significantly between 1979 and 2020, varying from + 1.16 h/year to + 8.25 h/year depending on the Köppen–Geiger class. The past 20 years (2000 forward) presented not only more consecutive hours under heat stress than the previous two decades in all the analyzed cities, but also a higher persistence of such conditions. The bioclimatology of thermal stress developed here may provide important guidelines to decision-makers for exploring adaptation strategies to increase societal resilience.

Spatial–Temporal Characteristics of Human Thermal Comfort in Xinjiang: Based on the Universal Thermal Climate Index from 1981 to 2019

Xinjiang is one of the world’s most sensitive and vulnerable regions to climate change. However, little is known about the current status and changes in thermal comfort conditions in this area. Using the Universal Thermal Climate Index (UTCI) derived from the newly available high-resolution dataset HiTiSEA, the spatial–temporal pattern and changes thereof over annual and seasonal scales across Xinjiang from 1981 to 2019 were evaluated. The results reveal that the distribution and change of thermal comfort in Xinjiang have apparent regional heterogeneity and seasonal characteristics. Across all scales, 7 of 10 UTCI thermal stress categories were observed, from slight cold stress to strong heat stress. Annually, the mean UTCI is 3 °C and has significantly increased at 0.37 °C decade−1. The mean number of comfortable days (CDs) is 114 days, with a range from 0 to 189 days. On the space scale, the Tarim Basin experiences the highest UTCI value, while the Ili River Valley, the north side of the Tianshan Mountains, and the peripheral areas of the Tarim Basin have a higher number of CDs. Seasonally, summer has the highest UTCI value, while winter is the lowest. The trend for all seasons is upward, and spring increases fastest. Results also indicate that air temperature has a positive correlation with climate comfort, and the influence of air temperature on climate comfort is most significant. Further research indicates that the range and intensity of population exposure to uncomfortable climates in Xinjiang have increased. The distribution and expansion of population exposure are similar to the population density. These findings contribute to a systematic understanding of the local climate environment and can be helpful for the assessment of the impact of climate change and optimize tourism development.

Green infrastructure modelling for UHI control to urban thermal comfort: a case study of Temanggung urban area

ABSTRACT The Temanggung urban area in Central Java (Indonesia) already has considerable urban Green Infrastructure (GI), but the phenomenon of Urban Heat Island (UHI) has expanded to 268% in the last seven years. This study explores the theoretical gaps related to urban thermal comfort by combining tree management modelling as the independent variable and existing urban morphology as the dependent variable to identify the right place for the right tree using ENVI-met v5 simulations. We use the Universal Thermal Climate Index (UTCI) to determine urban thermal comfort, and our results showed a temperature decrease from 37°C (strong heat stress) to 32.5°C–35.5°C (moderate heat stress) and an average decrease of 1°C–3.5°C. These results were obtained by simulating the placement pattern of substations, land use zoning, tree size composition, paying attention to the type of road surface material, wind direction and speed and direction of road orientation, average air temperature, and location of building masses. This study provides a basis for consideration to assist local governments and researchers in managing GI in Temanggung Urban Area to create comfortable urban thermal comfort for their residents.

Future heat extremes and impacts in a convection-permitting climate ensemble over Germany

Abstract. Heat extremes and associated impacts are considered the most pressing issue for German regional governments with respect to climate adaptation. We explore the potential of a unique high-resolution, convection-permitting (2.8 m), multi-GCM (global climate model) ensemble with COSMO-CLM (Consortium for Small-scale Modeling Climate Limited-area Modelling) regional simulations (1971–2100) over Germany regarding heat extremes and related impacts. We find a systematically reduced cold bias especially in summer in the convection-permitting simulations compared to the driving simulations with a grid size of 7 km and parametrized convection. The projected increase in temperature and its variance favors the development of longer and hotter heat waves, especially in late summer and early autumn. In a 2 ∘C (3 ∘C) warmer world, a 26 % (100 %) increase in the heat wave magnitude index is anticipated. Human heat stress (universal thermal climate index (UTCI) &gt; 32 ∘C) and region-specific parameters tailored to climate adaptation revealed a dependency on the major landscapes, resulting in significantly higher heat exposure in flat regions such as the Rhine Valley, accompanied by the strongest absolute increase. A nonlinear, exponential increase is anticipated for parameters characterizing strong heat stress (UTCI &gt; 32 ∘C, tropical nights, very hot days). Providing region-specific and tailored climate information, we demonstrate the potential of convection-permitting simulations to facilitate improved impact studies and narrow the gap between climate modeling and stakeholder requirements for climate adaptation.

Dynamically downscaled projection of urban outdoor thermal stress and indoor space cooling during future extreme heat

While projected urban air temperatures under climate change and urbanization have received attention, projections of pedestrian thermal stress are scarce and usually produced by statistical downscaling. In this study, we present and evaluate a dynamical downscaling methodology to assess urban outdoor thermal exposure. We dynamically downscale Earth system model output with a mesoscale weather, urban canopy and building energy model (WRF-BEP-BEM), then use the downscaled output as boundary conditions for a microscale model (TUF-Pedestrian) to determine metre-scale mean radiant temperature. Using this methodology, we assess outdoor heat exposure and air conditioning loading during typical heatwaves at the start and end of century in Phoenix and Toronto.Results reveal that air conditioning loading would double in Phoenix by the end of century under an RCP 8.5 climate and urban development scenario; and it may double in Toronto even without urban development. This is compounded by up to 2 additional hours/day of extreme heat stress in Phoenix (5.5 additional hours/day of strong heat stress in Toronto). Using our dynamical downscaling methodology, we find that projected climate change-induced increases in outdoor heat stress largely result from higher air temperatures (Phoenix: 69–87%; Toronto: 60–64%), with smaller contributions from increased mean radiant temperature and humidity.

Human thermo-physiological comfort assessment in Lisbon by local climate zones on very hot summer days

Extreme heat is a current and future issue on urban areas, with negative impacts on health and quality of life (increasing morbidity and mortality rates). This paper analyses day (12:00–15:00 h) and nighttime (00:00–03:00 h) thermo-physiological comfort (TC) conditions by Local Climate Zones (LCZ) in Lisbon during a particular Local Weather Type (LWT), very hot summer days. For this, 13 different microscale sample areas were chosen covering urban and non-urban land cover classes (LCZs 1–3, 4–6, 8, 9, A and B). Universal Thermal Climate Index (UTCI) and Mean Radiant Temperature (MRT) were modeled on SkyHelios software for 163 days between 2008 and 2014. Results show that during the day all urban LCZ samples depict the same average TC conditions (average UTCI of 34°C—strong heat stress) and densely wooded areas are 2°C cooler (average UTCI of 32°C—moderate heat stress). However, compact areas (LCZs 1–3) with low sky view factor and some vegetation (street trees) display lower percentages of area with higher thermo-physiological discomfort (TD) levels (83% with strong heat stress against 98% in LCZs 8 and 9 and 100% in LCZs 4–6). When considering the hottest days (air temperatures equal or above 35°C—75th percentile), the moderate heat stress class disappears in all samples and the very strong heat stress class appears only on urban areas, occupying between 12% and 16% on LCZs 1–3, 10%–22% on LCZs 4–6, 16%–22% on LCZs 8 and 9 on LCZ 9. During the nighttime period all samples show no thermal stress, favoring nocturnal physiological recovery. TC conditions in Lisbon are strongly influenced by solar radiation and wind, which explains the need to increase the shading area, preferably by trees, and to promote and preserve ventilation paths.