Exposure to ambient temperature and heat index in relation to DNA methylation age: A population-based study in Taiwan

BACKGROUND

Climate change caused an increase in ambient temperature in the past decades. Exposure to high ambient temperature could result in biological aging, but relevant studies in a warm environment were lacking. We aimed to study the exposure effects of ambient temperature and heat index (HI) in relation to age acceleration in Taiwan, a subtropical island in Asia.

METHODS

The study included 2,084 participants from Taiwan Biobank. Daily temperature and relative humidity data were collected from weather monitoring stations. Individual residential exposure was estimated by ordinary kriging. Moving averages of ambient temperature and HI from 1 to 180 days prior to enrollment were calculated to estimate the exposure effects in multiple time periods. Age acceleration was defined as the difference between DNA methylation age and chronological age. DNA methylation age was calculated by the Horvath's, Hannum's, Weidner's, ELOVL2, FHL2, phenotypic (Pheno), Skin & blood, and GrimAge2 (Grim2) DNA methylation age algorithms. Multivariable linear regression models, generalized additive models (GAMs), and distributed lag non-linear models (DLNMs) were conducted to estimate the effects of ambient temperature and HI exposures in relation to age acceleration.

RESULTS

Exposure to high ambient temperature and HI were associated with increased age acceleration, and the associations were stronger in prolonged exposure. The heat stress days with maximum HI in caution (80-90°F), extreme caution (90-103°F), danger (103-124°F), and extreme danger (>124°F) were also associated with increased age acceleration, especially in the extreme danger days. Each extreme danger day was associated with 571.38 (95 % CI: 42.63-1100.13), 528.02 (95 % CI: 36.16-1019.87), 43.9 (95 % CI: 0.28-87.52), 16.82 (95 % CI: 2.36-31.28) and 15.52 (95 % CI: 2.17-28.88) days increase in the Horvath's, Hannum's, Weidner's, Pheno, and Skin & blood age acceleration, respectively.

CONCLUSION

High ambient temperature and HI may accelerate biological aging.

Spatiotemporal variation in heatwaves and elderly population exposure across China

Heatwaves have been intensified worldwide due to climate change, posing great health risks, especially to elderly populations. However, in China, limited studies have employed the heat index to decipher the spatiotemporal trends of heatwaves and their impacts on the elderly population. By comparing the three heatwave definitions, this study aimed to evaluate the long-term spatiotemporal variations in heatwaves from 1964 to 2022 across China using the Excess Heat Factor (EHF). We took advantage of high-resolution reanalysis temperature data on the Google Earth Engine (GEE) platform to efficiently calculate the heatwaves. Our results revealed that the frequency and duration of heatwaves increased significantly in approximately 77 % of China's total area, with South China experiencing the most frequent and prolonged heatwaves. Conversely, in most areas, no significant trend was discerned in the growth of the maximum and average heatwave intensities. The total number of elderly people affected by heatwaves surged from approximately 11.96 million in 2001 to over 30.31 million in 2020, with an estimated additional 1.12 million older adults exposed to heatwaves annually across the nation (R2 = 0.60, p < 0.05). The population factor exhibited largest effect on the exposure of heatwaves, followed by climate effects and combined factors, with the corresponding explanatory power about 42.84 %, 34.85 % and 22.31 %, respectively. These individuals predominantly resided in the Northeast China, Southwest China, and South China. We also found geographical variations in heatwave exposure along elevations and land use types. These insights underscore the pressing necessity for formulating strategic interventions to mitigate the health threats presented by mounting heatwave exposure, especially for susceptible groups like the elderly in China.

The Effects of Heat Stress on Bakery Workers: A Systematic Review

Background

Working in hot environments can cause diseases and reduce performance by upsetting the balance of physiological parameters of workers' bodies. Bakers are among the people exposed to heat stress continuously and daily. This review study aimed to investigate the effect of heat stress on bakers.

Methods

In this review study, the related articles based on keywords were reviewed using "IranMedex", "Science Direct", "PubMed", "Scopus", "Web of Science", "SID", "Google Scholar", and "Magiran" databases from the years 2000 to 2021. The used search terms were "Heat stress", "Heat strain", "Heat exposure", "Heat waves", "Workplace", "Baker", and "health effects". In order to extract the required data, all parts of the articles have been reviewed.

Results

Out of the 16 studies reviewed in this study, 43.75% were cross-sectional, 25% were descriptive cross-sectional, and 31.25% were performed according to other study designs. In all of the studies, the WBGT index was used to assess ambient heat stress. In most studies, the mean exposure temperature was higher than the WBGT-ACGIH limit, especially among traditional bakery workers. The findings showed that exposure to thermal stress significantly affects some hematological parameters of blood, oxidative stress, heart rate, and body temperature.

Conclusion

The situation of heat stress in the bakery environment is worrying in terms of health and reduced productivity of employees. Therefore, it is essential to take the necessary preventive and control measures to reduce heat stress and the resulting strain.

Elevated heat indices resulting from hurricane-related defoliation: a case study

Defoliation caused by strong tropical cyclones can modify the partitioning of incident solar radiation between the sensible, latent, and substrate heat fluxes. While previous work has shown hurricane defoliation to warm near-surface air temperature along its track, this study more directly contextualizes the warming to human heat stress and exposure via the heat index (HI). For this case study, the spatial extent and temporal persistence of defoliation produced by Hurricane Laura (2020) in southwestern Louisiana was characterized using the normalized difference vegetation index (NDVI). The defoliated land surface was then assimilated into the Weather Research and Forecasting (WRF) model version 4.2 and compared to a control, normal-foliage simulation for the 30 days following landfall. Over southwest Louisiana, the largest HI increase occurred at 0600 UTC (1:00 AM LT) with an average increase of + 0.25 °C, and the exposure time to HI ≥ 30 °C increased by 8.1% after accounting for the defoliated landscape. Meanwhile, Cameron, Louisiana, the site of Laura's landfall where defoliation was most severe, cumulatively experienced an extra 33 h of HI values exceeding 26 °C, while mean HI increased by 1.2 °C at 0300 UTC. Additional WRF experiments were performed with altered "landfall" years of 2017 and 2018 to determine the sensitivity of defoliation-driven HI changes to the ambient synoptic conditions. While synoptic conditions modulated the magnitude of increase, HIs nonetheless experienced statistically significant increases in both hypothetical "landfall" years. Such findings are valuable for emergency managers and community health officials because overnight minimum temperatures are a strong indicator of heat mortality.

Identifying joint impacts of sun radiation, temperature, humidity, and rain duration on triggering mental disorders using a high-resolution weather monitoring system

BACKGROUND

Mental disorders (MDs) are behavioral or mental patterns that cause significant distress or impairment of personal functioning. Previously, temperature has been linked to MDs, but most studies suffered from exposure misclassification due to limited monitoring sites. We aimed to assess whether multiple meteorological factors could jointly trigger MD-related emergency department (ED) visits in warm season, using a highly dense weather monitoring system.

METHODS

We conducted a time-stratified, case-crossover study. MDs-related ED visits (primary diagnosis) from May-October 2017-2018 were obtained from New York State (NYS) discharge database. We obtained solar radiation (SR), relative humidity (RH), temperature, heat index (HI), and rainfall from Mesonet, a real-time monitoring system spaced about 17 miles (126 stations) across NYS. We used conditional logistic regression to assess the weather-MD associations.

RESULTS

For each interquartile range (IQR) increase, both SR (excess risk (ER): 4.9%, 95% CI: 3.2-6.7%) and RH (ER: 4.0%, 95% CI: 2.6-5.4%) showed the largest risk for MD-related ED visits at lag 0-9 days. While temperature presented a short-term risk (highest ER at lag 0-2 days: 3.7%, 95% CI: 2.5-4.9%), HI increased risk over a two-week period (ER range: 3.7-4.5%), and rainfall hours showed an inverse association with MDs (ER: -0.5%, 95% CI: 0.9-(-0.1)%). Additionally, we observed stronger association of SR, RH, temperature, and HI in September and October. Combination of high SR, RH, and temperature displayed the largest increase in MDs (ER: 7.49%, 95% CI: 3.95-11.15%). The weather-MD association was stronger for psychoactive substance usage, mood disorders, adult behavior disorders, males, Hispanics, African Americans, individuals aged 46-65, or Medicare patients.

CONCLUSIONS

Hot and humid weather, especially the joint effect of high sun radiation, temperature and relative humidity showed the highest risk of MD diseases. We found stronger weather-MD associations in summer transitional months, males, and minority groups. These findings also need further confirmation.

Heat exposure misclassification: Do current methods of classifying diurnal range in individually experienced temperatures and heat indices accurately reflect personal exposure?

Wearable sensors have been used to collect information on individual exposure to excessive heat and humidity. To date, no consistent diurnal classification method has been established, potentially resulting in missed opportunities to understand personal diurnal patterns in heat exposure. Using individually experienced temperatures (IET) and heat indices (IEHI) collected in the southeastern United States, this work aims to determine whether current methods of classifying IETs and IEHIs accurately characterize "day," which is typically the warmest conditions, and "night," which is typically the coolest conditions. IET and IEHI data from four locations were compared with the closest hourly weather station. Different day/night classifications were compared to determine efficacy. Results indicate that diurnal IET and IEHI ranges are higher than fixed-site ranges. Maximum IETs and IEHIs are warmer and occur later in the day than ambient conditions. Minimum IETs are lower and occur earlier in the day than at weather stations, which conflicts with previous assumptions that minimum temperatures occur at night. When compared to commonly used classification methods, a method of classifying day and night based on sunrise and sunset times best captured the occurrence of maximum IETs and IEHIs. Maximum IETs and IEHIs are often identified later in the evening, while minimum IETs and IEHIs occur throughout the day. These findings support future research focusing on nighttime heat exposure, which can exacerbate heat-related health issues, and diurnal patterns of personal exposure throughout the entire day as individual patterns do not necessarily follow the diurnal pattern seen in ambient conditions.

Individually experienced heat stress among elderly residents of an urban slum and rural village in India

The elderly are one of the most vulnerable groups to heat-related illnesses and mortality. In tropical countries like India, where heat waves have increased in frequency and severity, few studies have focused on the level of stress experienced by the elderly. The study presented here included 130 elderly residents of Kolkata slums and 180 elderly residents of rural villages about 75 km south of Kolkata. It used miniature monitoring devices to continuously measure temperature, humidity, and heat index experienced during everyday activities over 24-h study periods, during hot summer months. In the Kolkata slum, construction materials and the urban heat island effect combined to create hotter indoor than outdoor conditions throughout the day, and particularly at night. As a result, elderly slum residents were 4.3 times more likely to experience dangerous heat index levels (≥ 45°C) compared to rural village elderly. In both locations, the median 24-h heat indexes of active elderly were up to 2°C higher than inactive/sedentary elderly (F = 25.479, p < 0.001). Among Kolkata slums residents, there were no significant gender differences in heat exposure during the day or night, but in the rural village, elderly women were 4 times more likely to experience dangerous heat index levels during the hottest times of the day compared to elderly men. Given the decline in thermoregulatory capacity associated with aging and the increasing severity of extreme summer heat in India, these results forecast a growing public health challenge that will require both scientific and government attention.

Spatiotemporal dynamics of urban climate during the wet-dry season transition in a tropical African city

The Urban Heat Island effect has been the focus of several studies concerned with the effects of urbanisation on human and ecosystem health. Humidity, however, remains much less studied, although it is useful for characterising human thermal comfort, the Urban Dryness Island effect and vegetation development. Furthermore, variability in microscale climate due to differences in land cover is increasingly crucial for understanding urbanisation effects on the health and wellbeing of living organisms. We used regression analysis to investigate the spatial and temporal dynamics of temperature, humidity and heat index in the tropical African city of Kampala, Uganda. We gathered data during the wet to dry season transition from 22 locations that represent the wide range of urban morphological differences in Kampala. Our analysis showed that the advancement of the dry season increased variability of climate in Kampala and that the most built-up locations experienced the most profound seasonal changes in climate. This work stresses the need to account for water availability and humidity to improve our understanding of human and ecosystem health in cities.

Environmental effects on acute exacerbations of respiratory diseases: A real-world big data study

BACKGROUND

The effects of weather periods, race/ethnicity, and sex on environmental triggers for respiratory exacerbations are not well understood. This study linked the OneFlorida network (~15 million patients) with an external exposome database to analyze environmental triggers for asthma, bronchitis, and COPD exacerbations while accounting for seasonality, sex, and race/ethnicity.

METHODS

This is a case-crossover study of OneFlorida database from 2012 to 2017 examining associations of asthma, bronchitis, and COPD exacerbations with exposures to heat index, PM 2.5 and O 3. We spatiotemporally linked exposures using patients' residential addresses to generate average exposures during hazard and control periods, with each case serving as its own control. We considered age, sex, race/ethnicity, and neighborhood deprivation index as potential effect modifiers in conditional logistic regression models.

RESULTS

A total of 1,148,506 exacerbations among 533,446 patients were included. Across all three conditions, hotter heat indices conferred increasing exacerbation odds, except during November to March, where the opposite was seen. There were significant differences when stratified by race/ethnicity (e.g., for asthma in April, May, and October, heat index quartile 4, odds were 1.49 (95% confidence interval (CI) 1.42-1.57) for Non-Hispanic Blacks and 2.04 (95% CI 1.92-2.17) for Hispanics compared to 1.27 (95% CI 1.19-1.36) for Non-Hispanic Whites). Pediatric patients' odds of asthma and bronchitis exacerbations were significantly lower than adults in certain circumstances (e.g., for asthma during June - September, pediatric odds 0.71 (95% CI 0.68-0.74) and adult odds 0.82 (95% CI 0.79-0.85) for the highest quartile of PM 2.5).

CONCLUSION

This study of acute exacerbations of asthma, bronchitis, and COPD found exacerbation risk after exposure to heat index, PM 2.5 and O 3 varies by weather period, age, and race/ethnicity. Future work can build upon these results to alert vulnerable populations to exacerbation triggers.

Retrospection of heatwave and heat index

The frequency and intensity of extreme events especially heat waves (HW) are growing all around the world which ultimately poses a serious threat to the health of individuals. To quantify the effects of extreme temperature, appropriate information, and the importance of HW and heat index (HI) are carefully discussed for different parts of the world. Varied definitions of the HW and HI formula proposed and used by different countries are carried out systematically continent-wise. Different studies highlighted the number of definitions of HW; however, mostly used Steadman's formulae, which was developed in the late 1970s, for the calculation of HI that uses surface air temperature and relative humidity as climatic fields. Since then, dramatic changes in climatic conditions have been observed as evident from the ERA5 datasets which need to be addressed; likewise, the definition of HW, which is modified by the researchers as per the geographic conditions. It is evident from the ERA5 data that the temperature has increased by 1-2 °C as compared to the 1980s. There is a threefold increase in the number of heatwave days over most of the continents in the last 40 years. This study will help the researcher community to understand the importance of HW and HI. Furthermore, it opens the scope to develop an equation based on the present scenario keeping in mind the basics of an index as considered by Steadman.

Appraising the historical and projected spatiotemporal changes in the heat index in Bangladesh

Climate change-derived extreme heat phenomena are one of the major concerns across the globe, including Bangladesh. The appraisal of historical spatiotemporal changes and possible future changes in heat index (HI) is essential for developing heat stress mitigation strategies. However, the climate-health nexus studies in Bangladesh are very limited. This study was intended to appraise the historical and projected changes in HI in Bangladesh. The HI was computed from daily dry bulb temperature and relative humidity. The modified Mann-Kendal (MMK) test and linear regression were used to detect trends in HI for the observed period (1985-2015). The future change in HI was projected for the mid-century (2041-2070) for three Representative Concentration Pathway (RCP) scenarios, RCP 2.6, 4.5, and 8.5 using the Canadian Earth System Model Second Generation (CanESM2). The results revealed a monotonic rise in the HI and extreme caution conditions, especially in the humid summer season for most parts of Bangladesh for the observed period (1985-2015). Future projections revealed a continuous rise in HI in the forthcoming period (2041-2070). A higher and remarkable increase in the HI was projected in the northern, northeastern, and south-central regions. Among the three scenarios, the RCP 8.5 showed a higher projection of HI both in hot and humid summer compared to the other scenarios. Therefore, Bangladesh should take region-specific adaptation strategies to mitigate the impacts of HI.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s00704-021-03705-x.

Urban-rural moisture contrast: Regulator of the urban heat island and heatwaves' synergy over a mediterranean city

The current study observed the effect of the synergistic interaction of urban heat island (UHI) and heatwaves (HWs) which is different from the sum of their separate effects on the medium-sized town of Nicosia, Cyprus. From an analysis of hourly meteorological records of eight consecutive years (2007-2014) we defined HWs with respect to air temperature (T95-over the 95th percentile air temperatures) as well as the heat index (HI65-heat index over 65degC) and studied their effects on the local UHI phenomenon. Both heatwave types were characterized by increased air temperature, lower wind speed and increased absolute humidity. HWs defined using the heat index (HI65) occurred more frequently and persisted for a longer period of time. UHI was intensified to about 0.9-1.3 °C during daytime hours under both HW definitions which was attributed to the evaporation of dew deposited on the upper top layer of soil that suppressed higher temperatures in the rural station due to a prolonged cooling effect. Model estimates of dew formation overnight and evaporation in the morning hours are hypothesized to be the main contributing factor in keeping rural air temperatures lower, thus increasing the UHI intensity. The results emphasize the critical role of latent cooling and evapotranspiration as a mitigation factor affecting extreme local temperatures.

Preliminary findings of thermal safety in children's outdoor playhouses

Children are less proficient at regulating internal body temperatures, especially during physical activity, increasing the potential for heat-related illnesses during periods of elevated outdoor temperatures. Recent studies suggest that playgrounds and bounce houses create microclimates with potentially dangerous conditions elevating the risk of heat-related illnesses. The present pilot study extends the inquiry to children's outdoor playhouses to determine if the same capability of creating microclimatic conditions of elevated thermal risk exists. Air temperature (°C) and relative humidity (%) measurements were collected from inside two playhouses and the outside ambient environment over a 6-h period on a clear, warm, summer day. Measurements were used to calculate the National Weather Service (NWS) heat index for both playhouses and the outside environment. Results from a Kruskal-Wallis test demonstrated significant differences (p < 0.001) and post hoc test procedures indicated that playhouse A and playhouse B had significantly higher heat index values than the outside environment. Little is known about the thermal risks created by children's outdoor play equipment. This study adds to the preliminary work in this field, but continued research is warranted to fully understand the thermal safety of children's outdoor play equipment.

Association between human and animal thermal comfort indices and physiological heat stress indicators in dairy calves

Warm summer episodes have a significant effect on the overall health and well-being of young cattle; however, it is not known which temperature measure should be used for estimating heat stress in dairy calves. In this study, generalized linear mixed-effects models were used to estimate the relationships between thermal comfort indices and animal-based heat stress indicators in sixteen Holstein bull calves that were housed in individual calf hutches. Data were collected under continental weather characteristics over a 5-day period: day 1 (lower-temperature day), days 2 and 3 (heat stress days), and a 2-day post-stress period. Relative humidity, ambient temperature, the heat index, the humidex and five different temperature-humidity indices (THI) were used as thermal indices. Physiological variables monitored included respiratory rate, rectal temperature, ear skin temperature and heart rate. The heat index and the humidex measuring human thermal comfort were more closely associated with physiological measures than were the ambient temperature or the THIs (in case of heat index: R² = 0.87 for respiratory rate, R² = 0.63 for rectal temperature, R² = 0.70 for ear skin temperature, and R² = 0.78 for heart rate, respectively; in case of humidex: R² = 0.85 for respiratory rate, R² = 0.60 for rectal temperature, R² = 0.68 for ear skin temperature, and R² = 0.75 for heart rate, respectively). Based on our results, parameters of human outdoor comfort seem better to estimate heat stress in dairy calves in a continental region than those of THIs or ambient temperature.

A better indicator to measure the effects of meteorological factors on cardiovascular mortality: heat index

Although many studies have examined the correlation between temperature and mortality from cardiovascular diseases (CVD), other meteorological factors, such as relative humidity, may modify the relationship. Yet the studies on this aspect are relatively few. We chose a heat index (HI, which is an index that combines air temperature and relative humidity) as an alternative indicator of temperature, and used a distributed lag nonlinear model (DLNM) to analyze the combined effects of temperature and relative humidity on CVD mortality among all of the Beijing residents and subsociodemographic groups by age, sex, and occupation. The heat index can better reflect the human-perceived temperature when relative humidity is combined with air temperature. The results show that females, elderly people, and outdoor workers have higher vulnerability levels in regard to a high heat index. The strongest effect of heat index was found among females, for which the highest mortality risk was about 2.4 (95% CI 1.8-3) times greater than the lowest mortality risk. In addition, we found that there is a significant interaction effect of temperature and relative humidity on CVD mortality. The impact of extreme high temperature may be exacerbated by increases in humidity. Based on these results, we draw the risk level map of CVD death under different temperatures and grades of relative humidity. These findings may aid governments in the development of more accurate heat alerts and the provision of measures to prevent or reduce temperature-related deaths.

Investigating the effects of environmental factors on autism spectrum disorder in the USA using remotely sensed data

This study aimed to assess the association between exposures to outdoor environmental factors and autism spectrum disorder (ASD) prevalence in a diverse and spatially distributed population of 8-year-old children from the USA (n = 2,097,188) using the air quality index (AQI) of the US Environmental Protection Agency as well as satellite-derived data of PM_2.5 concentrations, sunlight, and maximum heat index. Multivariable logistic regression analyses were performed to determine whether the unhealthy AQI, PM_2.5, sunlight, and maximum heat index were related to the odds of ASD prevalence based on gender and race and taking into consideration the confounding factors of smoking and socioeconomic status. The logistic regression odds ratios for ASD per 10% increase in the unhealthy AQI were greater than 1 for all categories, indicating that unhealthy AQI is related to the odds of ASD prevalence. The odds ratio of ASD due to the exposure to the unhealthy AQI was higher for Asians (OR = 2.96, 95% CI = 1.11-7.88) than that for Hispanics (OR = 1.308, 95% CI = 0.607-2.820), and it was higher for Blacks (OR = 1.398, 95% CI = 0.827-2.364) than that for Whites (OR = 1.219, 95% CI = 0.760-1.954). The odds ratio of ASD due to the unhealthy AQI was slightly higher for males (OR = 1.123, 95% CI = 0.771-1.635) than that for females (OR = 1.117, 95% CI = 0.789-1.581). The effects of the unhealthy environmental exposures on the odds ratios of ASD of this study were inconclusive (i.e., statically insignificant; p value > 0.05) for all categories except for Asians. The odds ratios of ASD for Asians were increased by 5, 12, and 14% with increased levels of the environmental exposures of 10 μg/m³ of PM_2.5, 1000 kJ/m² of sunlight, and 1 °F of maximum heat index, respectively. The odds ratios of ASD prevalence for all categories, except for Asians, were increased with the inclusion of the smoking covariate, reflecting the effect of smoking on ASD prevalence besides the unhealthy environmental factors.

A Time Series Analysis of Associations between Daily Temperature and Crime Events in Philadelphia, Pennsylvania

Urban crime may be an important but overlooked public health impact of rising ambient temperatures. We conducted a time series analysis of associations between temperature and crimes in Philadelphia, PA, for years 2006-2015. We obtained daily crime data from the Philadelphia Police Department, and hourly temperature and dew point data from the National Centers for Environmental Information. We calculated the mean daily heat index and daily deviations from each year's seasonal mean heat index value. We used generalized additive models with a quasi-Poisson distribution, adjusted for day of the week, public holiday, and long-term trends and seasonality, to estimate relative rates (RR) and 95% confidence intervals. We found that the strongest associations were with violent crime and disorderly conduct. For example, relative to the median of the distribution of mean daily heat index values, the rate of violent crimes was 9% (95% CI 6-12%) higher when the mean daily heat index was at the 99th percentile of the distribution. There was a positive, linear relationship between deviations of the daily mean heat index from the seasonal mean and rates of violent crime and disorderly conduct, especially in cold months. Overall, these analyses suggest that disorderly conduct and violent crimes are highest when temperatures are comfortable, especially during cold months. This work provides important information regarding the temporal patterns of crime activity.

Spatiotemporal analysis of heat and heat wave effects on elderly mortality in Texas, 2006-2011

BACKGROUND

Heat and heat waves have been linked to the increased risk of deaths, hospital admissions, and emergency visits.

OBJECTIVES

This study presents a spatiotemporal analysis of heat and heat wave effects on elderly mortality (≥65years) in Texas.

METHODS

We compiled a six-year daily weather and mortality counts dataset from 254 counties in Texas during 2006-2011. Heat index (HI), a combination of temperature and relative humidity, was used as the exposure metric in this study. Associations between daily all-cause elderly mortality and daily maximum HI and heat waves (≥2days of county-specific daily maximum HI>95th percentiles) were examined using a quasi-Poisson regression. A Markov random field smoother was included in the model to account for spatial autocorrelations and spatial heterogeneity. The model also controlled for long-term trend and seasonality in mortality, and the effects of day of the week.

DISCUSSION

On average, the lag effect of heat on elderly mortality risk lasted up to 10days, and the cumulative heat effects started to increase rapidly when daily maximum HI exceeded the 90th percentile in Texas. Elderly living in Northwest Texas and parts of West Texas were at greater risk of elderly mortality attributable to heat waves, and the highest relative risk for elderly mortality occurred in El Paso County (4.70, 95% Confidence Interval=4.33, 5.10).

CONCLUSIONS

Our study indicates strong geographical variations of heat wave effects on elderly mortality risk in Texas.

The development of the Hong Kong Heat Index for enhancing the heat stress information service of the Hong Kong Observatory

This paper presents a study to develop a heat index, for use in hot and humid sub-tropical climate in Hong Kong. The study made use of hospitalization data and heat stress measurement data in Hong Kong from 2007 to 2011. The heat index, which is called Hong Kong Heat Index (HKHI), is calculated from the natural wet bulb temperature, the globe temperature, and the dry bulb temperature together with a set of coefficients applicable to the high humidity condition in the summer of Hong Kong. Analysis of the response of hospitalization rate to variation in HKHI and two other heat indices, namely Wet Bulb Globe Temperature (WBGT) and Net Effective Temperature (NET), revealed that HKHI performed generally better than WBGT and NET in reflecting the heat stress impact on excess hospitalization ratio in Hong Kong. Based on the study results, two reference criteria of HKHI were identified to establish a two-tier approach for the enhancement of the heat stress information service in Hong Kong.

An approach to evaluate the intra-urban thermal variability in summer using an urban indicator

Urban planners and managers need tools to evaluate the performance of the present state and future development of cities in terms of comfort and quality of life. In this paper, an approach to analyse the intra-urban summer thermal variability, using an urban planning indicator, is presented. The proportion of buildings and concrete surfaces in a specific buffer area are calculated. Besides, the relationship between urban and temperature indicators is investigated and used to produce thermal maps of the city. This approach is applied to the analysis of intra-urban variability in Florence (Italy), of two thermal indices (heat index and cooling degree days) used to evaluate impacts on thermal comfort and energy consumption for indoor cooling. Our results suggest that urban planning indicators can describe intra-urban thermal variability in a way that can easily be used by urban planners for evaluating the effects of future urbanization scenarios on human health.

Predicting indoor heat exposure risk during extreme heat events

Increased heat-related morbidity and mortality are expected direct consequences of global warming. In the developed world, most fatal heat exposures occur in the indoor home environment, yet little is known of the correspondence between outdoor and indoor heat. Here we show how summertime indoor heat and humidity measurements from 285 low- and middle-income New York City homes vary as a function of concurrent local outdoor conditions. Indoor temperatures and heat index levels were both found to have strong positive linear associations with their outdoor counterparts; however, among the sampled homes a broad range of indoor conditions manifested for the same outdoor conditions. Using these models, we simulated indoor conditions for two extreme events: the 10-day 2006 NYC heat wave and a 9-day event analogous to the more extreme 2003 Paris heat wave. These simulations indicate that many homes in New York City would experience dangerously high indoor heat index levels during extreme heat events. These findings also suggest that increasing numbers of NYC low- and middle-income households will be exposed to heat index conditions above important thresholds should the severity of heat waves increase with global climate change. The study highlights the urgent need for improved indoor temperature and humidity management.