Katerina Pantavou

Climate change and rising global temperature values lead to a cascade of effects on human health and well-being. Methodologies for assessing thermal conditions and identifying areas with increased thermal stress are important for enhancing the quality of life in urban environments. This study is aimed at developing a methodology that combines high-resolution simulation data with surface meteorological observations for application in urban thermal stress assessment. Eleven urban public sites within the metropolitan area of Athens, Greece (i.e., squares and parks) were simulated using the three-dimensional microclimate model ENVI-met. The model was validated using micrometeorological data from field campaigns conducted in summer, autumn and winter. The validation results confirmed that ENVI-met showed satisfactory performance for further research analysis. Subsequently, Physiologically Equivalent Temperature (PET) and Universal Thermal Climate Index (UTCI) were calculated using data from weather stations operated by the National Observatory of Athens and the Hellenic National Meteorological Service. PET and UTCI were then spatially interpolated using a mixed modeling and kriging method, with parameters optimized based on statistical validation metrics derived from the ENVI-met simulations. Finally, seasonal bioclimatic maps were produced to identify areas experiencing unfavorable thermal conditions. The spatial analysis revealed distinct seasonal patterns in the distribution of unfavorable thermal conditions across the Athens metropolitan area.

Climate change is one of the foremost challenges confronting humanity, with far-reaching consequences for ecosystems, economies, and societies worldwide. The steady rise of global temperatures is a clear sign of our changing climate with wide-ranging consequences, affecting everything from weather patterns and biodiversity to resources and human health. This study, performed in the frame of CLIMPACT project (Grant Agreement: 2023ΝΑ11900001), examines the impact of temperature rise on human thermal stress over the following years using the Universal Thermal Climate Index (UTCI). UTCI combines meteorological variables into a single value estimated in degrees Celsius and assigns it to a 10-point scale expressing the degree of human thermal stress. The scale ranges from -5 (‘extreme cold stress’) to +4 (‘extreme heat stress’) and includes a neutral category (0 – ‘no thermal stress’) and levels of increasing cold and heat stress. Climate change projections of the UTCI were estimated at 12:00 UTC using bias-corrected data of air temperature, relative humidity, wind speed and global solar radiation derived from the EURO-CORDEX regional climate model (RCM) simulations for Greece region and at a spatial resolution of ~11 km (0.11°). An ensemble of seven regional climate model simulations (three different regional models driven by five different global models) was used for the reference period (1991−2020) and the future period (2031−2060) in order to examine possible changes of UTCI estimations in the future. Both RCP4.5 and RCP8.5 greenhouse gases emissions scenario hypotheses (Representative Concentration Pathways, RCPs) were examined. The results show an increase of projected mean UTCI ranging from 1 ◦C to 1.5 ◦C [mean ± standard deviation (sd) = 1.2 ± 0.1 ◦C] across the country by the end of 2060 according to RCP4.5. This change is intensified under RCP8.5, with a projected increase in mean UTCI ranging from 1.4 ◦C to 2 ◦C (mean ± sd = 1.6 ± 0.1 ◦C) across the country. Areas with higher increase of mean UTCI are mountainous regions of the inland Greece, the northern and western part of the country and the islands of the Ionian and eastern Aegean Sea. In the future period, Greece is anticipated to experience a reduction in the percentage of cold stress and ‘no thermal stress’ days and an increase in the percentage of ‘strong’ (by 0.9% - RCP4.5; 1.2% - ­ RCP8.5), ‘very strong’ (by 2.9% - RCP4.5; 3.7% - RCP8.5), and ‘extreme’ (by 0.4% - RCP4.5; 0.5% - RCP8.5) heat stress days. The increase of heat stress is particularly pronounced during summer when the increase in the percentage of ‘very strong’ heat stress days ranges from 9.5% (RCP4.5) to 11.6% (RCP8.5) and of ‘extreme’ heat stress from 1.3% (RCP4.5) to 1.8% (RCP8.5). The findings underscore the significant impact of climate change on human thermal stress in Greece, with notable increases in projected heat stress. These projections highlight the urgent need for adaptive strategies to mitigate the health risks associated with rising thermal stress due to climate change.

The global rise in temperatures contributes to the increase of climate-sensitive diseases. Despite mitigation efforts, temperatures are projected to keep rising, highlighting the need for integrated methods to assess the impact of thermal environments on human health. This study summarizes the existing evidence on the statistical relationships (associations) between thermal indices and health outcomes. Medline, Scopus, and Web of Science were systematically searched until December, 2023 for studies examining the association between thermal indices and health outcomes in outdoor environments (protocol registration: PROSPERO CRD42023412470). The quality of the included studies was assessed using the United States National Institutes of Health Quality Assessment Tool. The search identified 5038 records, with 310 meeting eligibility criteria and examining 1143 associations. These associations represented 51 countries, primarily in North America (n = 448, 39.2%) and Europe (n = 399, 34.9%). Temperate climates (n = 597, 52.2%) were the most frequently examined. Seventeen indices were identified, with Apparent Temperature being the most common (141 publications, 634 associations). Frequently used indices included also Heat Index, Universal Thermal Climate Index, and Physiologically Equivalent Temperature. About half of the associations focused on mortality and half on morbidity. The most frequently examined associations were for diseases of the circulatory system (n = 304, 26.6%), all-cause morbidity/mortality (n = 288, 25.2%), and diseases of the respiratory system (n = 151, 13.2%). Among associations examining heat-related outcomes (n = 882), 57.8% (n = 510) suggested an increased risk of adverse health outcomes as indices increased, while for cold-related outcomes (n = 367), 44.1% (n = 162) suggested an increased risk as indices decreased. This systematic review reveals significant associations between thermal indices and health outcomes, indicating that thermal indices could be valuable tools for public health planning. However, the diversity in methodologies across studies highlights the need for standardization in methodology and reporting, including the reporting of non-significant findings.

The research on the thermal bioclimate is increasingly valuable in the context of climate change. Human well-being is threatened not only from direct exposure to extreme thermal conditions and complications from underlying health issues but also from disruptions of health and social services. This study aims at examining the thermal bioclimate in Greece. Data of ERA5-Land reanalysis dataset were used to estimate the Universal Thermal Climate Index (UTCI, in °C). The analysis covered a 30-year period (1991–2020) examining UTCI climatology and trends. Additionally, the intensity of two recent heatwaves which occurred in summers 2021 and 2023 was assessed. During the period 1991–2020, the UTCI equivalent temperature ranges between -49.8 °C and 51.9 °C [mean ± standard deviation (sd) = 13.3 ± 12.2 °C] classifying thermal stress from ‘extreme cold stress’ to ‘extreme heat stress’. Across the country, the mean UTCI ranges from 7.5 °C to 17.8 °C (mean ± sd = 13.3 ± 2.1 °C), with a decrease of 0.5 °C per latitude degree. Mountainous regions exhibit the lowest UTCI equivalent temperatures, while inland plains display higher UTCI equivalent temperatures, especially in the eastern regions of the country. An increasing trend in mean annual UTCI (mean = 0.05 °C/year) is identified, more pronounced in higher latitude regions. Both the 2021 and 2023 heatwaves were exceptionally severe, with about 99% of the population to experience mean UTCI equivalent temperatures falling within stress categories of ‘moderate heat stress’ and above. The 2023 heatwave set a new record with the highest absolute maximum UTCI (52.1 °C) and number of heat stress hours compared to the period 1991–2020. The bioclimatic maps developed in this study analyze the spatial variability in the thermal conditions across Greece identifying high-risk areas. These findings can contribute to impact studies for tourism, energy efficiency, urban design and public health purposes.

Exposure to a suboptimal outdoor thermal environment is associated with increased morbidity and mortality. This study aimed to examine the effect of the thermal environment on all-cause mortality in Cyprus. Daily mortality data were obtained from 2009 to 2018. Hourly meteorological data were retrieved from the ERA5-Land reanalysis database and air pollutant concentrations were obtained from the official air quality network of the Republic of Cyprus. Air temperature (Tair), the physiologically equivalent temperature (PET), and the universal thermal climate index (UTCI) were used to assess the thermal environment. Associations of Tair, PET, and UTCI with daily mortality were examined using negative binomial regression while adjusting for air quality. Mortality in the cold period (December to March) increased by 3.3% for each 1 °C decrease in Tair and by up to 1.8% for each 1 °C decrease in PET and UTCI (p value < 0.001). In the warm period (April to November), a 1 °C increase in Tair or in PET and UTCI was associated with an increase in mortality of up to 1.4% and 1.1% (p value < 0.001), respectively. The effect (increase in mortality) was more pronounced when the analysis focused on winter (3.6% per 1 °C decrease in Tair, 2.4% per 1 °C decrease in PET, and 2% per 1 °C decrease in UTCI) and summer (4.1% per 1 °C increase in Tair, 2.4% per 1 °C increase in PET, and 1.2% per 1 °C increase in UTCI). Males in cold periods and the elderly (older than 64 years) were more vulnerable. Awareness about the effects of the thermal environment on mortality, including those during the cold months of the year, should be enhanced.

The large number of thermal indices introduced in the literature poses a challenge to identify the appropriate one for a given application. The aim of this study was to examine the effectiveness of widely used indices in quantifying the thermal environment for operational weather applications within a Mediterranean climate. Eight indices (six simple and two thermo-physiological) were considered, i.e., apparent temperature, heat index, humidex, net effective temperature (NET), physiologically equivalent temperature (PET), universal thermal climate index (UTCI), wet-bulb globe temperature, and wind chill temperature. They were estimated using hourly meteorological data between 2010 and 2021, recorded in 15 stations from the Automatic Weather Station Network of the National Observatory of Athens in the Athens metropolitan area, Greece. The statistical analysis focused on examining indices’ sensitivity to variations of the thermal environment. NET, PET, and UTCI were evaluated as suitable for operational use, assessing both cool and warm environments, and extending their estimations to the entire range of their assessment scales. NET and PET often tended to classify thermal perception in the negative categories of their scales, with 63% of NET and 56% of PET estimations falling within the range of cool/slightly cool to very cold. UTCI estimations in the negative categories accounted for 25.8% (p < 0.001), while most estimations were classified in the neutral category (53.1%). The common occasions of extreme warm conditions in terms of both air temperature (Tair) and NET was 77.7%, Tair and UTCI 64.4%, and Tair and PET 33.6% (p < 0.001). According to the indices considered and the method followed, NET and UTCI satisfied sufficiently the requirements for operational use in the climate conditions of the Mediterranean climate.

Climate change raises concerns over the sustainability of the outdoor thermal environment and its impacts on societies. This study aims to examine the thermal conditions in Athens metropolitan area, Greece. Hourly data from 15 stations of the Automatic Weather Station Network of the National Observatory of Athens (2010–2021) were used to estimate the Net Effective Temperature (NET) and the Universal Thermal Climate Index (UTCI). The NET and UTCI were higher within the Athens basin (NET: mean ± sd = 15.3 ± 7.1 °C; UTCI: mean ± sd = 18.9 ± 10.4 °C) than in the surrounding area (NET: mean ± sd = 11.2 ± 9.3 °C; UTCI: mean ± sd = 13.4 ± 13.4 °C; p < 0.001). The highest numbers of hours with unfavorable warm conditions were found in Faliro (28.6%, NET; 27.7%, UTCI), Neos Kosmos (28.6%, NET; 27.4%, UTCI) and Patissia (28.6%, NET; 27.2%, UTCI). With respect to unfavorable cool conditions, the highest number was in Spata (65.1%, NET; 28.4%, UTCI).

Thermal indices are valuable tools for assessing thermal environments linked to applications related to architecture, planning, tourism, energy conservation and health. They combine meteorological variables into a single value which can be assigned to a category of an assessment scale expressing the predicted degree of human thermal discomfort, sensation or stress. The assessment scales include one indifference (neutral) category and negative and/or positive categories of increasing intensity of thermal feeling. The numerous indices that have been developed makes the selection of a suitable one for a specific application a complex issue. The aim of this study was to assess the effectiveness of several commonly used thermal indices for their operational use in weather applications in the Mediterranean climate of Greece. Hourly data (2010-2021) of air temperature (Tair, oC), relative humidity (Rh, %), wind speed (WS, m/s) and global solar radiation (SR, W/m2) recorded in 15 weather stations across the Athens metropolitan area of the Automatic Weather Stations Network of the National Observatory of Athens were used to calculate the indices. The indices should follow the following criteria: (a) be currently in common use, (b) be easily estimated operationally, i.e., short estimation time using Tair, Rh, WS and SR, and (c) provide exploitable results. Apparent temperature (AT), Heat Index (HI), Humidex (HU), Normal Effective Temperature (NET), Physiologically Equivalent Temperature (PET), Universal Thermal Climate Index (UTCI), Wet-Bulb Globe Temperature (WBGT) and Wind Chill Index (WCI) were identified as the most commonly used thermal indices in research and by weather services around the world. PET showed the highest computational demand compared to the other indices. At the first step, NET, PET and UTCI were assessed as more suitable for the climate of Athens (compared to AT, HI, HU, WBGT and WCI), extending their predictions to the entire range of their assessment scales. NET and PET tended to classify more often than UTCI thermal conditions in the negative categories of their assessment scales (67.8%-NET and 62.1%-PET versus 36.8%-UTCI; p<0.001) while most of UTCI values were classified in the neutral category (48.9%-UTCI versus 15.6%-NET and 15.1%-PET; p<0.001). Finally, more heat wave days were classified in accordance to Tair by NET (86.8%) and UTCI (84.5%) compared to PET (70.5%; p=0.014). According to the results of this study, NET and UTCI could be suggested as the best candidate indices for operational use in the climate of Athens, Greece.

Human Immunodeficiency Virus (HIV) interventions among people who use drugs (PWUD) often have spillover, also known as interference or dissemination, which occurs when one participant’s exposure affects another participant’s outcome. PWUD are often members of networks defined by social, sexual, and drug-use partnerships and their receipt of interventions can affect other members in their network. For example, HIV interventions with possible spillover include educational training about HIV risk reduction, pre-exposure prophylaxis, or treatment as prevention. In turn, intervention effects frequently depend on the network structure, and intervention coverage levels and spillover can occur even if not measured in a study, possibly resulting in an underestimation of intervention effects. Recent methodological approaches were developed to assess spillover in the context of network-based studies. This tutorial provides an overview of different study designs for network-based studies and related methodological approaches for assessing spillover in each design. We also provide an overview of other important methodological issues in network studies, including causal influence in networks and missing data. Finally, we highlight applications of different designs and methods from studies of PWUD and conclude with an illustrative example from the Transmission Reduction Intervention Project (TRIP) in Athens, Greece.