Characterizing prolonged heat effects on mortality in a sub-tropical high-density city, Hong Kong

Extreme Hot Weather Events and Risk of Hospitalization for Cardiovascular and Respiratory Diseases in Older People in Hong Kong in 2012-2018

BACKGROUND

The older population is more vulnerable to the impact of extreme hot weather events (EHWEs), although the impact on the frailer institutionalized older population was seldom assessed. Our objective was to assess the relationship between EHWEs and hospitalization risks among institutionalized and community-dwelling older people.

METHODS

We used territory-wide hospitalization records of Hong Kong from the year 2012 to 2018 to assess the associations between EHWEs and cardiovascular and respiratory disease hospitalizations in the population aged 65 or above. A very hot day (VHD) was defined as the daily maximum temperature ≥33 °C, and a hot night (HN) was defined as the daily minimum temperature ≥28 °C. We assessed whether prolonged exposure to high temperatures (defined as 3 consecutive VHDs (3VHD) or HNs (3HN)) was related to a higher risk of hospitalization over a lag period of 0-21 days. Time-stratified case-crossover design was used. Analyses were stratified by old age home (OAH) residence status.

RESULTS

Exposure to 3VHDs was related to a higher risk of cardiovascular disease admissions for community-dwelling older people [relative risk (RR): 1.09; 95% confidence interval (95%CI): 1.03-1.14 (lagged 4 days, ie, delayed manifestation up to 4 days)], whereas for OAH residents, the association could have a lag of 18 days (RR: 1.28; 95%CI: 1.05-1.54). For respiratory disease admissions, such relatively long-delayed relationship was not clearly observed.

CONCLUSIONS

The warming climate could increase healthcare demand in the long run. Frailer patients could present with a generally more marked and delayed onset of cardiovascular disease aggravation than the community-dwelling population.

Mapping Heat Vulnerability and Heat Risk for Neighborhood Health Risk Management in Urban Environment? Challenges and Opportunities

PURPOSE OF REVIEW

Heat vulnerability mapping (or heat risk mapping) is commonly used as a cost-effective tool to assess neighborhood health burdens for policy development and implementations. Some local governments have adopted this strategy to develop community action plans to cope with an increasing threat from heat exposure. However, various data/methods for mapping have yielded inconsistent results. For a compact city with high population density, issues from generic mapping techniques would become more apparent due to its complexity of social/environmental structures.

RECENT FINDINGS

We explored the similarities/differences in existing heat vulnerability mapping approaches. Previous models (1) failed to characterize extreme heat variations (e.g. days with different temperature extremes, difference between single hot days and prolonged heat events); (2) generally lacked a validation of associations between mapping results and various health outcomes (e.g. only relying on mortality data for validation but no validation of morbidities or clinical visits); (3) had a low ability to incorporate spatiotemporal variability of demographic patterns (e.g. difference in daytime/nighttime population patterns due to daily mobility); (4) were unable to adopt perceived heat exposure (e.g. Universal Thermal Climate Index); and (5) did not measure heat vulnerability at street-/building-levels even though 3-dimensional urban forms exist across major cities. Additionally, most applications (including those from local governments) were developed from a top-down perspective without a participatory design. A location-specific, evidence-based framework based on various exposure patterns and health outcomes with bottom-up strategies for implementations is needed for minimizing bias from "one-size-fits-all" strategies for action plans across high-density cities.

Suitable temperature indicator for adverse health impacts in sub-tropical cities: a case study in Hong Kong from 2010-2019

Heat-health warning systems and services are important preventive actions for extreme heat, however, global evidence differs on which temperature indicator is more informative for heat-health outcomes. We comprehensively assessed temperature predictors on their summer associations with adverse health impacts in a high-density subtropical city. Maximum, mean, and minimum temperatures were examined on their associations with non-cancer mortality and hospital admissions in Hong Kong during summer seasons 2010-2019 using Generalized Additive Models and Distributed Lag Non-linear Models. In summary, mean and minimum temperatures were identified as strong indicators for mortality, with a relative risk(RR) and 95% confidence interval(CI) of 1.037 (1.006-1.069) and 1.055 (1.019-1.092), respectively, at 95th percentile vs. optimal temperature. Additionally, minimum temperatures captured the effects of hospital admissions, RR1.009 (95%CI: 1.000- 1.018). In stratified analyses, significant associations were found for older adults, female sex, and respiratory-related outcomes. For comparison, there was no association between maximum temperature and health outcomes. With climate change and projected increase of night-time warming, the findings from this comprehensive assessment method are useful to strengthen heat prevention strategies and enhance heat-health warning systems. Other locations could refer to this comprehensive method to evaluate their heat risk, especially in highly urbanized environments and subtropical cities.

Long-Term Survival after Coronary Artery Surgical Revascularization-Does Ambient Temperature Matter?

Background and Objectives: The progression of global warming results in an increased exposure to extreme heat, leading to exaggeration of preexisting diseases and premature deaths. The aim of the study was to present possible risk factors for all-cause long-term mortality in patients who underwent surgical revascularization, including an assessment of the influence of ambient temperature exposure. Materials and Methods: Retrospective analysis included 153 (123 (80%) males and 30 (20%) females) patients who underwent off-pump revascularization and were followed for a median time of 2533 (1035-3250) days. The demographical, clinical data and ambient temperature exposure were taken into analysis for prediction of all-cause mortality. Individual exposure was calculated based on the place of habitation. Results: In the multivariate logistic regression model with backward stepwise elimination method, risk factors such as dyslipidaemia (p = 0.001), kidney disease (p = 0.005), age (p = 0.006), and body mass index (p = 0.007) were found to be significant for late mortality prediction. In addition to traditional factors, environmental characteristics, including tropical nights (p = 0.043), were revealed to be significant. Conclusions: High night-time ambient temperatures known as tropical nights may be regarded as additional long-term mortality risk factor after surgical revascularization.

Systematic identification of heat events associated with emergency admissions to enhance the heat-health action plan in a subtropical city: a data-driven approach

According to the United Nations Office for Disaster Risk Reduction (UNDRR), a heat-health action plan should address various impacts of hazards at different levels, including an early warning system to monitor risks and behaviour enhancement to increase disaster preparedness. It is necessary to comply with guidelines regarding heat duration/intensity. In this study, we developed a data-driven approach to rapidly and systematically estimate the impacts of various heat events on emergency admissions among the adult population (n = 7,086,966) in Hong Kong in order to enhance the heat-health action plan. Immediate, short-term, and long-term impacts determined by 1-day, 4-day, and 8-day windows were estimated to identify specific heat events suitable for early warnings. In addition, underestimated risk, determined by a continuous increase in heat risk after days without significant emergency admissions, was estimated to evaluate potential maladaptive behaviours among a specific subpopulation. Based on age- and gender-specific analyses, 1D, 1D1N, and 2D2N were observed to have a stronger immediate impact on emergency admissions. 1D1N and 2D2N also showed notable short-term and long-term impacts. Based on heat vulnerability factors (age and gender), 2D2N was a higher-priority extreme heat event for early warning measures than 1D1N. Furthermore, men aged 19 to 64 had the highest underestimated risk. Specifically, they had IRR values of 1.113 [1.087, 1.140], 1.061 [1.035, 1.087], and 1.069 [1.043, 1.095] during lag days 3-5 of 3D2N, respectively, possibly due to a lack of adaptive behaviour. By adopting our approach, the duration of heat events with significant health impacts can be identified in order to further enhance relevant heat stress information. This framework can be applied to other cities with a similar background for rapid assessment.

Visits to the accident and emergency department in hot season of a city with subtropical climate: association with heat stress and related meteorological variables

BACKGROUND

Literature reporting the association between heat stress defined by universal thermal climate index (UTCI) and emergency department visits is mainly conducted in Europe. This study aimed to investigate the association between heat stress, as defined by the UTCI, and visits to the accident and emergency department (AED) in Hong Kong, which represents a subtropical climate region.

METHODS

A retrospective study involving 13,438,846 AED visits in the public sector from May 2000 to September 2016, excluding 2003 and 2009, was conducted in Hong Kong. Age-sex-specific ANCOVA models of daily AED rates on heat stress and prolonged heat stress, adjusting for air quality, prolonged poor air quality, typhoon, rainstorm, year, day of the week, public holiday, summer vacation, and fee charging, were used.

RESULTS

On a day with strong heat stress (32.1 °C ≤ UTCI ≤ 38.0 °C), the AED visit rate (per 100,000) increased by 0.9 (95% CI: 0.5, 1.3) and 1.7 (95% CI: 1.3, 2.1) for females and males aged 19-64 and 4.1 (95% CI: 2.7, 5.4) and 4.1 (95% CI: 2.6, 5.6) for females and males aged ≥ 65, while keeping other variables constant. On a day with very strong heat stress (38.1 °C ≤ UTCI ≤ 46.0 °C), the corresponding rates increased by 0.6 (95% CI: 0.1, 1.2), 2.2 (95% CI: 1.7, 2.7), 4.9 (95% CI: 3.1, 6.7), and 4.7 (95% CI: 2.7, 6.6), respectively. The effect size of heat stress associated with AED visit rates was negligible among those aged ≤ 18. Heat stress showed the greatest effect size for males aged 19-64 among all subgroups.

CONCLUSION

Biothermal condition from heat stress was associated with the health of the citizens in a city with a subtropical climate and reflected in the increase of daily AED visit. Public health recommendations have been made accordingly for the prevention of heat-related AED visits.

Predicting Emergency Department Utilization among Older Hong Kong Population in Hot Season: A Machine Learning Approach

Previous evidence suggests that temperature is associated with the number of emergency department (ED) visits. A predictive system for ED visits, which takes local temperature into account, is therefore needed. This study aimed to compare the predictive performance of various machine learning methods with traditional statistical methods based on temperature variables and develop a daily ED attendance rate predictive model for Hong Kong. We analyzed ED utilization among Hong Kong older adults in May to September from 2000 to 2016. A total of 103 potential predictors were derived from 1- to 14-day lag of ED attendance rate and meteorological and air quality indicators and 0-day lag of holiday indicator and month and day of week indicators. LASSO regression was used to identify the most predictive temperature variables. Decision tree regressor, support vector machine (SVM) regressor, and random forest regressor were trained on the selected optimal predictor combination. Deep neural network (DNN) and gated recurrent unit (GRU) models were performed on the extended predictor combination for the previous 14-day horizon. Maximum ambient temperature was identified as a better predictor in its own value than as an indicator defined by the cutoff. GRU achieved the best predictive accuracy. Deep learning methods, especially the GRU model, outperformed conventional machine learning methods and traditional statistical methods.

Effect and attributable burden of hot extremes on bacillary dysentery in 31 Chinese provincial capital cities

BACKGROUND

High atmospheric temperature has been associated with the occurrence of bacillary dysentery (BD). Recent studies have suggested that hot extremes may influence health outcomes, however, none have examined the association between hot extremes and BD risk, especially at the national level.

OBJECTIVES

To assess the effect and attributable burden of hot extremes on BD cases and to identify populations at high risk of BD.

METHODS

Daily incident BD data of 31 provincial capital cities from 2010 to 2018 were collected from the Chinese Center for Disease Control and Prevention, weather data was obtained from the fifth generation of the European Re-Analysis Dataset. Three types of hot extremes, including hot day, hot night, and hot day and night, were defined according to single or sequential occurrence of daytime hot and nighttime hot within 24 h. A two-stage analytical strategy combined with distributed lag non-linear models (DLNM) was used to evaluate city-specific associations and national pooled estimates.

RESULTS

Hot extremes were significantly associated with the risk of BD on lagged 1-6 days. The overall cumulative relative risk (RR) was 1.136 [95% confidence interval (CI): 1.022, 1.263] for hot day, 1.181 (95% CI: 1.019, 1.369) for hot night, and 1.154 (95% CI: 1.038, 1.283) for hot day and night. Northern residents, females, and children younger than or equal to 14 years old were vulnerable under hot night, southern residents were vulnerable under hot day, and males were vulnerable under hot day and night. 1.854% (95% CI: 1.294%, 2.205%) of BD cases can be attributable to hot extremes, among which, hot night accounted for a large proportion.

CONCLUSIONS

Hot extremes may significantly increase the incidence risk and disease burden of BD. Type-specific protective measures should be taken to reduce the risk of BD, especially in those we found to be particularly vulnerable.

Impact of low-intensity heat events on mortality and morbidity in regions with hot, humid summers: a scoping literature review

The objective of this study is to determine the impacts of low-intensity heat on human health in regions with hot, humid summers. Current literature has highlighted an increase in mortality and morbidity rates during significant heat events. While the impacts on high-intensity events are established, the impacts on low-intensity events, particularly in regions with hot, humid summers, are less clear. A scoping review was conducted searching three databases (PubMed, EMBASE, Web of Science) using key terms based on the inclusion criteria. We included papers that investigated the direct human health impacts of low-intensity heat events (single day or heatwaves) in regions with hot, humid summers in middle- and high-income countries. We excluded papers written in languages other than English. Of the 600 publications identified, 33 met the inclusion criteria. Findings suggest that low-intensity heatwaves can increase all-cause non-accidental, cardiovascular-, respiratory- and diabetes-related mortality, in regions experiencing hot, humid summers. Impacts of low-intensity heatwaves on morbidity are less clear, with research predominantly focusing on hospitalisation rates with a range of outcomes. Few studies investigating the impact of low-intensity heat events on emergency department presentations and ambulance dispatches were found. However, the data from a limited number of studies suggest that both of these outcome measures increase during low-intensity heat events. Low-intensity heat events may increase mortality. There is insufficient evidence of a causal effect of low-intensity heat events on increasing morbidity for a firm conclusion. Further research on the impact of low-intensity heat on morbidity and mortality using consistent parameters is warranted.

In the Subtropical Monsoon Climate High-Density City, What Features of the Neighborhood Environment Matter Most for Public Health?

Urbanization and climate change have been rapidly occurring globally. Evidence-based healthy city development is required to improve living quality and mitigate the adverse impact of the outdoor neighborhood environment on public health. Taking Guangzhou as an example to explore the association of neighborhood environment and public health and preferably to offer some implications for better future city development, we measured ten environmental factors (temperature (T), wind-chill index (WCI), thermal stress index (HSI), relative humidity (RH), average wind speed (AWS), negative oxygen ions (NOI), PM2.5, luminous flux (LF), and illuminance (I)) in four seasons in four typical neighborhoods, and the SF-36 health scale was employed to assess the physical and mental health of neighborhood residents in nine subscales (health transition(HT), physiological functions (PF), general health status (GH), physical pain (BP), physiological functions (RP), energy vitality (VT), mental health (MH), social function (SF), and emotional functions (RE)). The linear mixed model was used in an analysis of variance. We ranked the different environmental factors in relation to aspects of health and weighted them accordingly. Generally, the thermal environment had the greatest impact on both physical and mental health and the atmospheric environment and wind environment had the least impact on physical health and mental health, respectively. In addition, the physical health of the resident was more greatly affected by the environment than mental health. According to the results, we make a number of strategic suggestions for the renewal of the outdoor neighborhood environment in subtropical monsoon climate high-density cities and provide a theoretical basis for improving public health through landscape architecture at the neighborhood scale.

The associations between social, built and geophysical environment and age-specific dementia mortality among older adults in a high-density Asian city

Background

Although socio-environmental factors which may affect dementia have widely been studied, the mortality of dementia and socio-environmental relationships among older adults have seldom been discussed.

Method

A retrospective, observational study based on territory-wide register-based data was conducted to evaluate the relationships of four individual-level social measures, two community-level social measures, six short-term (temporally varying) environmental measures, and four long-term (spatially varying) environmental measures with dementia mortality among older adults in a high-density Asian city (Hong Kong), for the following decedents: (1) all deaths: age >= 65, (2) “old-old”: age > = 85, (3) “mid-old”: aged 75–84, and (4) “young-old”: aged 65–74.

Results

This study identified 5438 deaths (3771 old-old; 1439 mid-old; 228 young-old) from dementia out of 228,600 all-cause deaths among older adults in Hong Kong between 2007 and 2014. Generally, regional air pollution, being unmarried or female, older age, and daily O₃ were associated with higher dementia mortality, while more urban compactness and greenness were linked to lower dementia mortality among older adults. Specifically, being unmarried and the age effect were associated with higher dementia mortality among the “old-old”, “mid-old” and “young-old”. Regional air pollution was linked to increased dementia mortality, while urban compactness and greenness were associated with lower dementia mortality among the “old-old” and “mid-old”. Higher daily O₃ had higher dementia mortality, while districts with a greater percentage of residents whose native language is not Cantonese were linked to lower dementia mortality among the “old-old”. Economic inactivity was associated with increased dementia mortality among the “young-old”. Gender effect varied by age.

Conclusion

The difference in strengths of association of various factors with dementia mortality among different age groups implies the need for a comprehensive framework for community health planning. In particular, strategies for air quality control, usage of greenspace and social space, and activity engagement to reduce vulnerability at all ages are warranted.

Geospatial context of social and environmental factors associated with health risk during temperature extremes: Review and discussion

This study reviews forty-six publications between 2008 and 2017 dealing with socio-environmental impacts on adverse health effects of temperature extremes, in a geospatial context. The review showed that most studies focus on extremely hot weather but lack analysis of how spatial heterogeneity across a region can influence cold mortality/morbidity. There are limitations regarding the use of temperature datasets for spatial analyses. Only a few studies have applied air temperature datasets with high spatial resolution to health studies, but none of these studies have used anthropogenic heat as a factor for analysis of health risk. In addition, the elderly is generally recognized as a vulnerable group in most studies, but the interaction between old age and temperature risk varies by location. Other socio-demographic factors such as low income, low education and accessibility to community shelters may also need to be considered in the future. There are only a few studies which investigate the interaction between temperature and air pollution in a geospatial context, despite the fact that this is a known interaction that can influence health risk under extreme weather. In conclusions, although investigation of temperature effects on health risk is already at the "mature stage", studies of socio-environmental influences on human health under extreme weather in a geospatial context is still being investigated. A comprehensive assessment is required to analyse how the spatial aspects of the geophysical and social environments can influence human health under extreme weather, in order to develop a better community plan and health protocols for disaster preparedness.

Heat wave trends in Southeast Asia during 1979-2018: The impact of humidity

In tropics, especially Southeast Asia (SEA), heat wave (HW) research is seriously scarce although several global studies have projected this region to be greatly susceptible to increasing HW events under climate change scenarios. Using the recently released ERA5 reanalysis data, we find that in most parts of SEA, HWs are becoming more frequent, longer-lasting and stronger, no matter using dry-bulb or wet-bulb temperatures to define HW. The increasing trends of HW characteristics based on minimum temperatures are larger than those based on maximum temperatures, suggesting an alarming situation of anomalously warm night. HW characteristics based on wet-bulb temperatures show higher increasing rates in the IndoChina Peninsula and Malay Peninsula than those based on dry-bulb temperatures. Nearly all HW characteristics are significantly correlated with El Niño index, but Indian Ocean Dipole only significantly impacts HW characteristics based on wet-bulb temperature in Java. Results derived from other reanalysis products exhibit general agreement with those from ERA5, lending support to the findings reported herein. This study highlights the different role of humidity in changing HW trends in different regions of SEA, and calls for attention to the associated risk of increasing nighttime temperatures during HWs.

Integrated urban services: Experience from four cities on different continents

Rapid urbanization combined with climate change necessitates new types of urban services that make best use of science and technology. The Integrated Urban Hydro-Meteorological, Climate and Environmental Services and systems are a new initiative from the World Meteorological Organization (WMO) that seeks to provide science-based integrated urban services supporting safe, healthy and resilient cities. Various cities have already started development and implementation of such Integrated Urban Services and successfully test and use them following specific requirements of local stakeholders. This paper demonstrates the novel concept and approach of Integrated Urban Hydro-Meteorological, Climate and Environmental Services (IUS) from a set of four case study cities: Hong Kong, Toronto, Mexico City and Paris, that use different IUS configurations with good existing practice. These cities represent a range of countries, climates and geophysical settings. The aggregate main joint similarities of the IUS in these cities and synergy of the cities' experience, achievements and research findings are presented, as well as identification of existing gaps in knowledge and further research needs. A list of potential criteria for identifying and classifying IUS demonstration cities is proposed. It will aid future, more detailed analysis of the IUS experience, and selection of additional demonstration cities.

A new paradigm regarding testicular thermoregulation in ruminants?

Increased testicular temperature reduces percentages of morphologically normal and motile sperm and fertility. Specific sperm defects appear at consistent intervals after testicular hyperthermia, with degree and duration of changes related to intensity and duration of the thermal insult. Regarding pathogenesis of testicular hyperthermia on sperm quality and fertility, there is a long-standing paradigm that: 1) testes operate near hypoxia; 2) blood flow to the testes does not increase in response to increased testicular temperature; and 3) an ensuing hypoxia is the underlying cause of heat-induced changes in sperm morphology and function. There are very limited experimental data to support this paradigm, but we have data that refute it. In 2 × 3 factorial studies, mice and rams were exposed to two testicular temperatures (normal and increased) and three concentrations of O₂ in inspired air (hyperoxia, normoxia and hypoxia). As expected, increased testicular temperature had deleterious effects on sperm motility and morphology; however, hyperoxia did not prevent these changes nor did hypoxia replicate them. In two follow-up experiments, anesthetized rams were sequentially exposed to: 1) three O₂ concentrations (100, 21 and 13% O₂); or 2) three testicular temperatures (33, 37 and 40 °C). As O₂, decreased, testis maintained O₂ delivery and uptake by increasing testicular blood flow and O₂ extraction, with no indication of anaerobic metabolism. Furthermore, as testicular temperature increased, testicular metabolic rate nearly doubled, but increased blood flow and O₂ extraction prevented testicular hypoxia and anaerobic metabolism. In conclusion, our data, in combination with other reports, challenged the paradigm that testicular hyperthermia fails to increase testicular blood flow and the ensuing hypoxia disrupts spermatogenesis.

The impact of extremely hot weather events on all-cause mortality in a highly urbanized and densely populated subtropical city: A 10-year time-series study (2006-2015)

BACKGROUND

The impact of heatwaves on public health has led to an urgent need to describe extremely hot weather events (EHWEs) and evaluate their health impacts.

METHODS

In Hong Kong, a very hot day (VHD) can be defined when the daily maximum temperature ≥ 33 °C, and a hot night (HN) can be identified if the daily minimum temperature ≥ 28 °C. Three lengths of time, nine combinations of VHD and HN, and four categories of occurrence intervals between two EHWEs were considered over 2006-2015. The daily relative risk (RR) of all-cause mortality was estimated using Poisson generalized additive regression models, controlling for both short-term and long-term trends in temperature as well as four air pollutants. Lagged effects of the representative EHWEs were further examined for their association with mortality. Subgroup analysis was conducted for different sex and age groups.

RESULTS

Significant associations with raised mortality risks were observed for a single HN, while stronger associations with mortality were observed as significant for five or more consecutive VHDs/HNs. More HNs between the consecutive VHDs also significantly amplified the impact on mortality, with the strongest association observed for EHWEs characterized as 2D3N, and the effect significantly lagged for five days. Therefore, with identifiable health impacts, three thresholds (5VHDs, 5HNs, & 2D3N) were determined to be representative of identical types of EHWEs in Hong Kong. Furthermore, by taking 2 (3) consecutive VHDs (HNs) as one daytime (nighttime) EHWE event, those occurring consecutively without non-hot days (nights) in between were found to be significantly associated with excess mortality risks. Moreover, females and older adults were determined to be relatively more vulnerable to all defined EHWEs.

CONCLUSIONS

Among all the observed significant heat-mortality associations in highly urbanized cities, EHWEs that occurred during the nighttime, with extended length, consecutively without any break in between, or in the pattern of 2D3N might require the meteorological administration, healthcare providers, and urban planners to work interactively.

Development of the Adjusted Wind Chill Equivalent Temperature (AWCET) for cold mortality assessment across a subtropical city: validation and comparison with a spatially-controlled time-stratified approach

Background

Global warming has reduced the adaptability of the people living in subtropical regions to cope up with cold stress due to lengthening of hot days and shortening of transition period from hot to cold weather. However, existing studies on measuring cold stress are based on biometeorological indices designed for temperate regions. This may overestimate the impact of wind chill on mortality risk in subtropical cities.

Methods

This study developed an Adjusted Wind Chill Equivalent Temperature (AWCET) index. A spatially-controlled time-stratified approach was applied to evaluate the ability of AWCET for estimating cold mortality in subtropical cities, based on a mortality dataset (2008–2012) in Hong Kong.

Results

The use of AWCET could indicate increase in all-cause, cardiovascular, respiratory, and cancer-related mortality risk during the days with average temperature < = 1st [11.0 °C], <= 3rd [12.6 °C] and < = 5th [13.4 °C] percentiles. The results were stable and consistent based on both log-linear and curve-linear relationships between AWCET and mortality risk. AWCET was also compared with the New Wind Chill Equivalent Temperature (NWCET) designed for temperate regions, and has found that higher magnitude of mortality risk would be found when using AWCET for assessing all-cause and cause-specific mortality in Hong Kong, for days with average temperature < = 1st, <= 3rd and < = 5th percentiles.

Conclusions

AWCET is validated to be effective to access cold mortality in the context of subtropical cities. The use of AWCET may enhance the cold weather warning system in subtropical cities, as a supplementary tool to help demonstrating small administrative-level perceived temperature with volunteered geographic information.

Urban environmental influences on the temperature-mortality relationship associated mental disorders and cardiorespiratory diseases during normal summer days in a subtropical city

Temperature is associated with mortality risk across cities. However, there is lack of study investigating the summer effect on mortality associated with mental/behavioral disorders, especially in cities with subtropical climate. In addition, summer mortality in subtropical cities is different from tropical cities, and previous studies have not investigated the urban environmental inequality on heat mortality associated with mental/behavioral disorders. A register-based study was developed to estimate the temperature effects on decedents on days with 50^th percentile of average daily temperature between 2007 and 2014 in Hong Kong (n = 133,359). Poisson regression was firstly applied to estimate the incidence rate ratio (IRR) from the summer temperature effects on all-cause mortality, cardiovascular mortality, respiratory mortality, and mortality associated with mental/behavioral disorders. For a 1 °C increase in average temperature on days with temperature ≥ 24.51 °C, IRRs of mortality associated with mental and behavioral disorders on lag 0 and lag 1 days were 1.033 [1.004, 1.062] and 1.030 [1.002, 1.060], while temperature effects on cardiovascular mortality and respiratory mortality during normal summer days (not extreme heat events) were not significant. A further investigation with linear regression has shown that decedents with mental/behavioral disorders on higher temperature days resided in areas with lower percentage of sky view, lower percentage of vegetation cover, higher level of neighborhood-level PM_2.5, higher level of neighborhood-level NO, and higher level of neighborhood-level black carbon (BC). In order to develop protocols for community healthcare based on the "Leaving no one behind" scheme documented in the 2016 Sustainable Development Goals report of the United Nations, it is necessary to include heat effects on mental/behavioral disorders, especially people with dementia, for community planning and healthcare development.

Assessing spatial variability of extreme hot weather conditions in Hong Kong: A land use regression approach

The number of extreme hot weather events have considerably increased in Hong Kong in the recent decades. The complex urban context of Hong Kong leads to a significant intra-urban spatial variability in climate. Under such circumstance, a spatial understanding of extreme hot weather condition is urgently needed for heat risk prevention and public health actions. In this study, the extreme hot weather events of Hong Kong were quantified and measured using two indicators - very hot day hours (VHDHs) and hot night hours (HNHs) which were counted based on the summertime hourly-resolved air temperature data from a total of 40 weather stations (WSs) from 2011 to 2015. Using the VHDHs and HNHs at the locations of the 40 WSs as the outcome variables, land use regression (LUR) models are developed to achieve a spatial understanding of the extreme hot weather conditions in Hong Kong. Land surface morphology was quantified as the predictor variables in LUR modelling. A total of 167 predictor variables were considered in the model development process based on a stepwise multiple linear regression (MLR). The performance of resultant LUR models was evaluated via cross validation. VHDHs and HNHs were mapped at the community level for Hong Kong. The mapping results illustrate a significant spatial variation in the extreme hot weather conditions of Hong Kong in both the daytime and nighttime, which indicates that the spatial variation of land use configurations must be considered in the risk assessment and corresponding public health management associated with the extreme hot weather.

Spatiotemporal influence of temperature, air quality, and urban environment on cause-specific mortality during hazy days

Haze is an extreme weather event that can severely increase air pollution exposure, resulting in higher burdens on human health. Few studies have explored the health effects of haze, and none have investigated the spatiotemporal interaction between temperature, air quality and urban environment that may exacerbate the adverse health effects of haze. We investigated the spatiotemporal pattern of haze effects and explored the additional effects of temperature, air pollution and urban environment on the short-term mortality risk during hazy days. We applied a Poisson regression model to daily mortality data from 2007 through 2014, to analyze the short-term mortality risk during haze events in Hong Kong. We evaluated the adverse effect on five types of cause-specific mortality after four types of haze event. We also analyzed the additional effect contributed by the spatial variability of urban environment on each type of cause-specific mortality during a specific haze event. A regular hazy day (lag 0) has higher all-cause mortality risk than a day without haze (odds ratio: 1.029 [1.009, 1.049]). We have also observed high mortality risks associated with mental disorders and diseases of the nervous system during hazy days. In addition, extreme weather and air quality contributed to haze-related mortality, while cold weather and higher ground-level ozone had stronger influences on mortality risk. Areas with a high-density environment, lower vegetation, higher anthropogenic heat, and higher PM_2.5 featured stronger effects of haze on mortality than the others. A combined influence of haze, extreme weather/air quality, and urban environment can result in extremely high mortality due to mental/behavioral disorders or diseases of the nervous system. In conclusion, we developed a data-driven technique to analyze the effects of haze on mortality. Our results target the specific dates and areas with higher mortality during haze events, which can be used for development of health warning protocols/systems.