Impact of heat waves on nonaccidental deaths in Jinan, China, and associated risk factors

Heat wave, fine particulate matter, and cardiovascular disease mortality: A time-stratified case-crossover study in Shenzhen, China

BACKGROUND

In the context of global warming, the frequency of heat wave and the concentration of fine particulate matter (PM2.5) have increased, and more people are co-exposed to air pollution and extreme heat. However, the interaction between heat wave and PM2.5 on cardiovascular disease (CVD) mortality remained largely unknown.

METHODS

We conducted a time-stratified case-crossover study of 40,169 CVD deaths in Shenzhen, China between 2013 and 2022. Meteorological data and air pollutants information were obtained based on the residential addresses from the validated grid datasets. A total of 21 heat wave definitions were constructed using various relative temperature thresholds and durations. Conditional logistic regression was used to evaluate the independent and interactive effects of exposure to heat wave and PM2.5 on CVD mortality.

RESULTS

The odds ratios (ORs) and 95 % confidence intervals (CIs) for CVD mortality associated with heat waves ranged from 1.17 (95 % CI: 1.001,1.36) to 1.91 (95 % CI: 1.42, 2.56). For every increase of 10 µg/m³ in PM2.5 exposure, the ORs (95 % CI) for CVD mortality ranged from 1.0283 (95 % CI: 1.0162, 1.0406) to 1.029 (95 % CI: 1.0169, 1.0413). There was a synergistic effect between heat wave and PM2.5 exposures on CVD mortality. It was estimated that up to 2.03 % of CVD deaths were attributable to heat wave and PM2.5 levels exceeding the interim target 4 in the World Health Organization air quality guidelines (≥ 25 μg/m3), resulting in 816 premature deaths. Females and individuals over 75 years old were vulnerable populations.

CONCLUSIONS

Heat wave and PM2.5 exposures individually and synergistically contributed to increased risks of CVD mortality. Our findings indicate that reducing exposure to both heat wave and PM2.5 may yield significant health benefits and prevent a significant portion of premature deaths from CVDs.

The synergistic effect of high temperature and relative humidity on non-accidental deaths at different urbanization levels

Numerous studies have examined the impact of temperature on mortality, yet research on the combined effect of temperature and humidity on non-accidental deaths remains limited. This study investigates the synergistic impact of high temperature and humidity on non-accidental deaths in China, assessing the influence of urban development and urbanization level. Utilizing the distributed lag nonlinear model (DLNM) of quasi-Poisson regression, we analyzed the relationship between Wet Bulb Globe Temperature (WBGT) and non-accidental deaths in 30 Chinese cities from 2010 to 2016, including Guangzhou during 2012-2016. We stratified temperature and humidity across these cities to evaluate the influence of varying humidity levels on deaths under high temperatures. Then, we graded the duration of heat and humidity in these cities to assess the impact of deaths with different durations. Additionally, the cities were categorized based on gross domestic product (GDP), and a vulnerability index was calculated to examine the impact of urban development and urbanization level on non-accidental deaths. Our findings reveal a pronounced synergistic effect of high temperature and humidity on non-accidental deaths, particularly at elevated humidity levels. The synergies of high temperature and humidity are extremely complex. Moreover, the longer the duration of high temperature and humidity, the higher the risk of non-accidental death. Furthermore, areas with higher urbanization exhibited lower relative risks (RR) associated with the synergistic effects of heat and humidity. Consequently, it is imperative to focus on damp-heat related mortality among vulnerable populations in less developed regions.

Knowledge, Attitudes, and Practices of Military Personnel Regarding Heat-Related Illness

INTRODUCTION

Heat-related illnesses are a global concern, affecting millions of people and leading to numerous deaths annually. Since military personnel are exposed to heat, the purpose of the study was to evaluate military personnel's knowledge, attitudes, and practices (KAP) related to heat-related illnesses. Their KAP may help to prevent heat-related illness.  Methods: We conducted a cross-sectional study using a structured online questionnaire on 168 military personnel who were training and working in a high-temperature and high-humidity environment all year round in Jeddah, Saudi Arabia. The questionnaire assessed the KAP and associated factors and was distributed as a Google Form.

RESULTS

The mean knowledge score was 9.04 (range = 2-13, SD = 1.832), the mean awareness score was 9.61 (range = 4-15, SD = 2.415), and the mean practice score was 3.39 (range = 0-6, SD = 1.703). Most participants correctly identified symptoms (n=130; 77.4%). In terms of attitudes, most participants showed a good attitude (n=151; 81%), though 24.4% did not perceive the risk. Regarding practice, most were attentive to heat-related illness signs and hydration(75.6%), but there were gaps in receiving briefings from doctors (69%) and adequate guidance on treatment (56%). There was a split opinion on whether commanders adjust field activities based on temperature warnings (54.8% Yes, 45.2% No). There were no significant differences in knowledge scores based on age or educational level (both p>0.05), while some age and education-related differences were noted in practice scores (p<0.05). There was a positive correlation between knowledge and attitudes (r = 0.222, p = 0.004), knowledge and practices (r = 0.165, p = 0.033), and attitudes and practice (r=0.326, p < 0.001).

CONCLUSION

Our study found that military personnel generally possess good knowledge of heat-related illnesses and good attitudes and practices concerning heat-related illnesses. However, there are areas in need of improvement, and enhancing awareness and practical implementation of preventive measures, along with the development of precise guidance and protocols, should involve active collaboration between military commanders and healthcare professionals.

Urbanization-driven increases in summertime compound heat extremes across China

Summertime extreme heat events exert severe impacts on the natural environment and human society, especially in densely populated and highly urbanized regions. While previous studies have focused on independent heat day/night, there is a lack of attention to the changes in compound events with cooccurring daytime and nighttime extreme temperature on the same day. In this study, we examine the spatio-temporal changes of summertime compound heat extremes (including compound heat day and compound heatwave) across China, with a particular focus on 20 major urban agglomerations (UAs), and quantify the urbanization effects on these changes. We find that the frequency and fraction of compound heat events show obvious spatial disparities across China. The compound heat events occur more frequently in highly populated and urbanized areas such as the Pearl River Delta. Moreover, the frequency and fraction of compound heat events have significantly increased in recent decades in most parts of China, especially in more developed UAs. These intensifying trends have even accelerated in more recent decades. Our further investigations suggest that most UAs of China experienced an intensifying urbanization effect on compound heat events, and few UAs in northwestern and central China (e.g., UAs of the north Tianshan mountain and the middle reaches of the Yangtze River) display a weakening effect of urbanization. Our findings highlight the important role of urbanization in increasing compound heat extremes and suggest that the increasing threats of compound events in urban areas should be given more attention under the context of global warming and local urbanization.

Effects of extreme temperature on respiratory diseases in Lanzhou, a temperate climate city of China

Under the global climate warming, extreme weather events occur more and more frequently. Epidemiological studies have proved that extreme temperature is strongly correlated with respiratory diseases. We evaluated extreme-temperature effect on respiratory emergency room (ER) visits for 5 years in Lanzhou, a northwest temperate climate city of China from January 1st, 2013, to August 31st, 2017. We built a distributed lag non-linear model (DLNM) to evaluate the lag effect up to 30 days. Results showed the relative risk (RR) of respiratory disease always reached the maximum at lag 0 day and decreased to 1.0 at lag 5 days. Extremely low temperature showed the lag effect of 22 days and the maximum RR was 1.415 (95% CI 1.295-1.546) at lag 0 day. Extremely high temperature showed the lag effect of 7 days and the maximum RR was 1.091 (95% CI 1.069-1.114) at lag 0 day. The elders (age > 65 years) were at the greatest risk to extreme temperatures and the response were very acute. Children (age ≤ 15 years) were at the lowest risk but the lag effect lasted the longest lag days than other subgroups. Males showed longer-term lag effect and higher RR than females. Our study indicated that the extremely low temperature has a significantly greater effect on respiratory diseases than extremely high temperature.

Effective analysis of a community-based intervention during heat waves to improve knowledge, attitude and practice in a population in Licheng District, Jinan City, China

Background

Intervention strategies that focus on coping with continuous heat wave threats have been implemented in many countries. Despite these efforts, we still lack evidence concerning intervention efficacy. A Heat Wave Intervention Program (HWIP) that impacts knowledge, attitude and practice (KAP) was designed, and its effectiveness during heat waves was evaluated.

Methods

A stratified two-stage probability proportion to size sampling method was employed to analyze an intervention group and a control group. Two cross-sectional surveys, which included questions about heat waves in 2014 and 2015, were analyzed using difference-in-difference (DID) analysis.

Results

Mean KAP scores among participants with different demographic characteristics in the intervention group were higher in 2015 than those in 2014. Further analysis by DID found that implementing interventions was positively associated with knowledge (ß = 0.387, P < 0.001) and attitude (ß = 0.166, P < 0.01).

Conclusion

Intervention measures can significantly promote levels of knowledge and attitude. However, as the practice level, most of the sub-groups showed no significant differences for net values between in the intervention group and control group. A cost-benefit analysis was suggested as future work to check the effectiveness of the program. Therefore, further improvement measures should be targeted towards the populations to enable them to effectively cope with the heat waves.

The Use of a Quasi-Experimental Study on the Mortality Effect of a Heat Wave Warning System in Korea

Many cities and countries have implemented heat wave warning systems to combat the health effects of extreme heat. Little is known about whether these systems actually reduce heat-related morbidity and mortality. We examined the effectiveness of heat wave alerts and health plans in reducing the mortality risk of heat waves in Korea by utilizing the discrepancy between the alerts and the monitored temperature. A difference-in-differences analysis combined with propensity score weighting was used. Mortality, weather monitoring, and heat wave alert announcement data were collected for 7 major cities during 2009–2014. Results showed evidence of risk reduction among people aged 19–64 without education (−0.144 deaths/1,000,000 people, 95% CI: −0.227, −0.061) and children aged 0–19 (−0.555 deaths/1,000,000 people, 95% CI: −0.993, −0.117). Decreased cardiovascular and respiratory mortality was found in several subgroups including single persons, widowed people, blue-collar workers, people with no education or the highest level of education (university or higher). No evidence was found for decreased all-cause mortality in the population (1.687 deaths/1,000,000 people per day; 95% CI: 1.118, 2.255). In conclusion, heat wave alerts may reduce mortality for several causes and subpopulations of age and socio-economic status. Further work needs to examine the pathways through which the alerts impact subpopulations differently.

Health impact of climate change in cities of middle-income countries: the case of China

BACKGROUND

This review examines the human health impact of climate change in China. Through reviewing available research findings under four major climate change phenomena, namely extreme temperature, altered rainfall pattern, rise of sea level and extreme weather events, relevant implications for other middle-income population with similar contexts will be synthesized.

SOURCES OF DATA

Sources of data included bilingual peer-reviewed articles published between 2000 and 2018 in PubMed, Google Scholar and China Academic Journals Full-text Database.

AREAS OF AGREEMENT

The impact of temperature on mortality outcomes was the most extensively studied, with the strongest cause-specific mortality risks between temperature and cardiovascular and respiratory mortality. The geographical focuses of the studies indicated variations in health risks and impacts of different climate change phenomena across the country.

AREAS OF CONTROVERSY

While rainfall-related studies predominantly focus on its impact on infectious and vector-borne diseases, consistent associations were not often found.

GROWING POINTS

Mental health outcomes of climate change had been gaining increasing attention, particularly in the context of extreme weather events. The number of projection studies on the long-term impact had been growing.

AREAS TIMELY FOR DEVELOPING RESEARCH

The lack of studies on the health implications of rising sea levels and on comorbidity and injury outcomes warrants immediate attention. Evidence is needed to understand health impacts on vulnerable populations living in growing urbanized cities and urban enclaves, in particular migrant workers. Location-specific climate-health outcome thresholds (such as temperature-mortality threshold) will be needed to support evidence-based clinical management plans and health impact mitigation strategies to protect vulnerable communities.

Health-risk perception and its mediating effect on protective behavioral adaptation to heat waves

Ensuring spontaneously adjusting behaviors of the public in their daily life in response to heat waves is an important aspect of successful public health intervention under climate change. However, the current response behavior guidance released by the government is insufficient because of the limited understanding of public perceptions of heat-related risk and the motivating factors for the public's diverse adaptive behaviors. Here, we conducted a survey on the behavioral adaptations of 3065 urban residents in response to heat waves in Jinan, which is a typical city suffering from a hot climate. We provided evidence on the current state of residents' perception of heat waves and the mechanism of how risk perception mediates individual behavioral intentions upon exposure to high ambient temperatures. We found that the mediating effects of risk perception varied significantly with respect to different types of adaptive behaviors. Concern behaviors appeared be motivated completely by the mediating effects of perceived concern (b = 0.45, p < 0.01 for concerns about health guidelines; b = 0.36, p < 0.01 for concerns about the weather forecast) and severity (b = 0.11, p < 0.01 for concerns about health guidelines), while outdoor activity could be consciously adjusted according to temperature changes without those mediating effects (p > 0.05). Indoor cooling behaviors and transportation behaviors are partially mediated by risk perception (b = -0.04, p < 0.01; b = 0.08, p < 0.01; b = 0.08, p < 0.01 for indoor fan usage, use of air-conditioned buses, and use of private cars, respectively). The conclusions could help determine more targeted and detailed interventions to enhance public behavioral adjustments, including participation in adaption to and emergency preparedness for extreme temperature under the ongoing climate changes.

Impact of heat on mortality and morbidity in low and middle income countries: A review of the epidemiological evidence and considerations for future research

Heat waves and high air temperature are associated with increased morbidity and mortality. However, the majority of research conducted on this topic is focused on high income areas of the world. Although heat waves have the most severe impacts on vulnerable populations, relatively few studies have studied their impacts in low and middle income countries (LMICs). The aim of this paper is to review the existing evidence in the literature on the impact of heat on human health in LMICs. We identified peer-reviewed epidemiologic studies published in English between January 1980 and August 2018 investigating potential associations between high ambient temperature or heat waves and mortality or morbidity. We selected studies according to the following criteria: quantitative studies that used primary and/or secondary data and report effect estimates where ambient temperature or heat waves are the main exposure of interest in relation to human morbidity or mortality within LMICs. Of the total 146 studies selected, eighty-two were conducted in China, nine in other countries of East Asia and the Pacific, twelve in South Asia, ten in Sub-Saharan Africa, eight in the Middle East and North Africa, and seven in each of Latin America and Europe. The majority of studies (92.9%) found positive associations between heat and human morbidity/mortality. Additionally, while outcome variables and study design differed greatly, most utilized a time-series study design and examined overall heath related morbidity/mortality impacts in an entire population, although it is notable that the selected studies generally found that the elderly, women, and individuals within the low socioeconomic brackets were the most vulnerable to the effects of high temperature. By highlighting the existing evidence on the impact of extreme heat on health in LMICs, we hope to determine data needs and help direct future studies in addressing this knowledge gap. The focus on LMICs is justified by the lack of studies and data studying the health burden of higher temperatures in these regions even though LMICs have a lower capacity to adapt to high temperatures and thus an increased risk.

Influence of Heat Waves on Daily Hospital Visits for Mental Illness in Jinan, China-A Case-Crossover Study

Background: Given that more frequent and intensive extreme heat events have been projected based on climate change modeling, it is of significance to have a better understanding of the association between heat waves and mental illnesses. This study aimed to explore the effects of heat waves on daily hospital visits for mental illness in the summer of 2010 in Jinan, China. Methods: A symmetric bidirectional case-crossover study was firstly conducted to determine the relationship between daily hospital visits for mental illness and heat waves in Jinan in 2010. Multifactor logistic regression analysis was then used to analyze the influencing factors for daily hospital visits for mental illness during the heat wave periods. Results: Multivariable analysis showed that the heat wave events were associated with an increased risk of mental illness. The largest odds ratios (ORs) of the heat waves for daily hospital visits for mental illness were 2.231 (95% confidence interval (CI): 1.436–3.466) at a 3-day lag, 2.836 (95% CI: 1.776–4.525) at a 2-day lag, 3.178 (95% CI: 1.995–5.064) at a 3-day lag, and 2.988 (95% CI: 2.158–4.140) at a 2-day lag for the first, second, third, and fourth heat waves, respectively. The elderly, urban residents, outdoor workers, and singles may be high-risk populations for developing heat wave-related mental illness. Conclusions: Our study has supported that there is a positive association between heat waves and hospital visits for mental illness in the study site. Age, home address, occupation, and marital status were associated with daily hospital visits for mental illness during the heat wave periods.

Mortality effects of heat waves vary by age and area: a multi-area study in China

BACKGROUND

Many studies have reported an increased mortality risk from heat waves comparing with non-heat wave days. However, how much the mortality rate change with the heat intensity-vulnerability curve-is still unknown. Such unknown information makes the related managers impossible to assess scientifically life losses from heat waves, consequently fail in conducting suitable integrated risk management measures.

METHODS

We used the heat wave intensity index (HWII) to characterize quantitatively the heat waves, then applied a distributed lag non-linear model to explore the area-specific definition of heat wave, and developed the vulnerability models on the relationships between HWII and mortality by age and by area. Finally, Monte Carlo method was run to assess and compare the event-based probabilistic heat wave risk during the periods of 1971-2015 and 2051-2095.

RESULTS

We found a localized definition of heat wave for each corresponding area based on the minimum AIC (Akaike information criterion). Under the local heat wave events, the expected life loss during 1971-2015 does distinguish across areas, and decreases consistently in the order of WZ Chongqing, PK Nanjing and YX Guangzhou for each age group. More specifically, for the elders (≥65), the average annual loss (AAL) (and 95% confidence interval) would be 61.3 (30.6-91.9), 38 (3.8-72.2) and 18.7 (7.3-30) deaths per million people. With two stresses from warming and aging in future China, the predicted average AAL of the elders under four Representative Carbon Pathways (2.6, 4.5, 6.0, and 8.5) during 2051-2095 would be 2460, 1675, 465 deaths per million for PK Nanjing, YX Guangzhou and WZ Chongqing, respectively, approximately becoming 8~ 90 times of the AAL during 1971-2015.

CONCLUSION

This study found that the non-linear HWII-mortality relationships vary by age and area. The heat wave mortality losses are closely associated with the social-economic level. With the increasing extreme climatic events and a rapid aging trend in China, our findings can provide guidance for policy-makers to take appropriate regional adaptive measures to reduce health risks in China.

Ambient high temperature and mortality in Jinan, China: A study of heat thresholds and vulnerable populations

BACKGROUND

Understanding the health consequences of continuously rising temperatures-as is projected for China-is important in terms of developing heat-health adaptation and intervention programs. This study aimed to examine the association between mortality and daily maximum (T_max), mean (T_mean), and minimum (T_min) temperatures in warmer months; to explore threshold temperatures; and to identify optimal heat indicators and vulnerable populations.

METHODS

Daily data on temperature and mortality were obtained for the period 2007-2013. Heat thresholds for condition-specific mortality were estimated using an observed/expected analysis. We used a generalised additive model with a quasi-Poisson distribution to examine the association between mortality and T_max/T_min/T_mean values higher than the threshold values, after adjustment for covariates.

RESULTS

T_max/T_mean/T_min thresholds were 32/28/24°C for non-accidental deaths; 32/28/24°C for cardiovascular deaths; 35/31/26°C for respiratory deaths; and 34/31/28°C for diabetes-related deaths. For each 1°C increase in T_max/T_mean/T_min above the threshold, the mortality risk of non-accidental-, cardiovascular-, respiratory, and diabetes-related death increased by 2.8/5.3/4.8%, 4.1/7.2/6.6%, 6.6/25.3/14.7%, and 13.3/30.5/47.6%, respectively. Thresholds for mortality differed according to health condition when stratified by sex, age, and education level. For non-accidental deaths, effects were significant in individuals aged ≥65 years (relative risk=1.038, 95% confidence interval: 1.026-1.050), but not for those ≤64 years. For most outcomes, women and people ≥65 years were more vulnerable.

CONCLUSION

High temperature significantly increases the risk of mortality in the population of Jinan, China. Climate change with rising temperatures may bring about the situation worse. Public health programs should be improved and implemented to prevent and reduce health risks during hot days, especially for the identified vulnerable groups.

The impact of temperature extremes on mortality: a time-series study in Jinan, China

OBJECTIVE

To investigate the relationship between temperature extremes and daily number of deaths in Jinan, a temperate city in northern China.

METHODS

Data ondaily number of deaths and meteorological variables over the period of 2011-2014 were collected. Cold spells or heat waves were defined as ≥3 consecutive days with mean temperature ≤5th percentile or ≥95th percentile, respectively. We applied a time-series adjusted Poisson regression to assess the effects of extreme temperature on deaths.

RESULTS

There were 152 150 non-accidental deaths over the study period in Jinan, among which 87 607 people died of cardiovascular disease, 11 690 of respiratory disease, 33 001 of stroke and 6624 of chronic obstrutive pulmonary disease (COPD). Cold spells significantly increased the risk of deaths due to non-accidental mortality (RR 1.08, 95% CI 1.06 to 1.11), cardiovascular disease (RR 1.06, 95% CI 1.03 to 1.10), respiratory disease (RR 1.19, 95% CI 1.11 to 1.27), stroke (RR 1.11, 95% CI 1.06 to 1.17) and COPD (RR 1.27, 95% CI 1.16 to 1.38). Heat waves significantly increased the risk of deaths due to non-accidental mortality (RR 1.02, 95% CI 1.00 to 1.05), cardiovascular disease (RR 1.03, 95% CI 1.00 to 1.06) and stroke (RR 1.06, 95% CI 1.00 to 1.13). The elderly were more vulnerable during heat wave exposure; however, vulnerability to cold spell was the same for the whole population regardless of age and gender.

CONCLUSIONS

Both cold spells and heat waves have increased the risk of death in Jinan, China.

The prevalence of heat-related cardiorespiratory symptoms: the vulnerable groups identified from the National FINRISK 2007 Study

The prevalence of heat-related cardiorespiratory symptoms among vulnerable groups is not well known. We therefore estimated the prevalence of heat-related cardiorespiratory symptoms among the Finnish population and their associations with social and individual vulnerability factors. The data came from the National FINRISK 2007 Study, in which 4007 men and women aged 25-74 answered questions on heat-related cardiorespiratory symptoms in the Oulu Cold and Heat Questionnaire 2007. Logistic regression was used to calculate odds ratios (ORs), their 95 % confidence intervals (CIs), and model-predicted prevalence figures. The prevalence of heat-related cardiorespiratory symptoms was 12 %. It increased with age, from 3 % at the age of 25 years to 28 % at the age of 75 years. The symptoms were associated with pre-existing lung (OR 3.93; CI 3.01-5.13) and cardiovascular diseases (OR 2.27; 1.78-2.89); being a pensioner (OR 2.91; 1.65-5.28), unemployed (OR 2.82; 1.47-5.48), or working in agriculture (OR 2.27; 1.14-4.46) compared with working in industry; having only basic vs academic education (OR 1.98; 1.31-3.05); being female (OR 1.94; 1.51-2.50); being heavy vs light alcohol consumer (OR 1.89; 1.02-3.32); undertaking hard vs light physical work (OR 1.48;1.06-2.07); and being inactive vs active in leisure time (OR 1.97; 1.39-2.81). The adjusted prevalence of symptoms showed a wide range of variation, from 3 to 61 % depending on sex, age, professional field, education, and pre-existing lung and cardiovascular diseases. In conclusion, heat-related cardiorespiratory symptoms are commonly perceived among people with pre-existing lung or cardiovascular disease, agricultural workers, unemployed, pensioners, and people having only basic education. This information is needed for any planning and targeting measures to reduce the burden of summer heat.

A Cross-Sectional Study of Heat Wave-Related Knowledge, Attitude, and Practice among the Public in the Licheng District of Jinan City, China

Knowledge, attitude, and practice (KAP) are three key components for reducing the adverse health impacts of heat waves. However, research in eastern China regarding this is scarce. The present study aimed to evaluate the heat wave-related KAP of a population in Licheng in northeast China. This cross-sectional study included 2241 participants. Data regarding demographic characteristics, KAP, and heat illnesses were collected using a structured questionnaire. Univariate analysis and unconditional logistic regression models were used to analyze the data. Most residents had high KAP scores, with a mean score of 12.23 (standard deviation = 2.23) on a 17-point scale. Urban women and participants aged 35-44 years had relatively high total scores, and those with high education levels had the highest total score. There was an increased risk of heat-related illness among those with knowledge scores of 3-5 on an 8-point scale with mean score of 5.40 (standard deviation = 1.45). Having a positive attitude toward sunstroke prevention and engaging in more preventive practices to avoid heat exposure had a protective interaction effect on reducing the prevalence of heat-related illnesses. Although the KAP scores were relatively high, knowledge and practice were lacking to some extent. Therefore, governments should further develop risk-awareness strategies that increase awareness and knowledge regarding the adverse health impact of heat and help in planning response strategies to improve the ability of individuals to cope with heat waves.