Number Of Heat Waves Research Articles

Climatology of Wet-Bulb Globe Temperature and Associated Heat Waves in the U.S. Great Plains

Abstract Extreme heat such as that seen in the United States and Europe in summer 2022 can have significant impacts on human health and infrastructure. The Occupational Safety and Health Administration (OSHA) and the U.S. Army use wet-bulb globe temperature (WBGT) to quantify the impact of heat on workers and inform decisions on workload. WBGT is a weighted average of air temperature, natural wet-bulb temperature, and black globe temperature. A local hourly, daily, and monthly WBGT climatology will allow those planning outdoor work to minimize the likelihood of heat-related disruptions. In this study, WBGT is calculated from the ERA5 reanalysis and is validated by the Oklahoma Mesonet and found to be adequate. Two common methods of calculating WBGT from meteorological observations are compared. The Liljegren method has a larger diurnal cycle than the Dimiceli method, with a peak WBGT about 1°F higher. The high- and extreme-risk categories in the southern U.S. Great Plains (USGP) have increased from 5 days per year to 15 days from 1960 to 2020. Additionally, the largest increases in WBGT are occurring during DJF, potentially lengthening the warm season in the future. Heat wave definitions based on maximum, minimum, and mean WBGT are used to calculate heat wave characteristics and trends with the largest number of heat waves occurring in the southern USGP. Further, the number of heat waves is generally increasing across the domain. This study shows that heat wave days based on minimum WBGT have increased significantly which could have important impacts on human heat stress recovery.

Determination of heat wave definition temperatures in Spain at an isoclimatic level: time trend of heat wave duration and intensity across the decade 2009–2018

BackgroundIn line with WHO guidelines for the implementation of public health prevention plans targeted at the impacts of high temperatures, a heat wave definition temperature (Tthreshold) was calculated for 182 so-called “isoclimatic zones” (IZ) in Spain. As the dependent variable for determining this Tthreshold, we analysed daily all-cause mortality data (ICD-10: A00-R99) for each IZ across the period 2009–2018. The independent variable used was the mean value of the maximum daily temperature of the summer months recorded at meteorological observatories in each IZ. We used Box–Jenkins models to ascertain mortality anomalies, and scatterplots to link these anomalies to the temperatures at which they occurred, thereby determining the Tthreshold for each IZ. We then calculated how many heat waves had occurred in each IZ, as well as their intensity, and analysed their time trend over this period.ResultsThe results showed that in 52.5% of the IZ, the percentile of the maximum temperatures series of the summer months to which Tthreshold corresponded was below the 95th percentile of the meteorological heat wave definition in Spain: indeed, it only coincided in 30.7% of cases. The geographical distribution of these percentiles displayed great heterogeneity as a consequence of the local factors that influence the temperature–mortality relationship. The trend in the number of heat waves analysed indicated an overall increase in Spain at a rate of 3.9 heat waves per decade, and a similar rise in mean annual intensity of 9.5 °C/decade. These time-trend values were higher than those yielded by analysing the trend in meteorological heat waves based on the 95th percentile.ConclusionsThe results obtained in this study indicate the need to use a heat wave definition based on epidemiological temperature–mortality studies, rather than on values based on meteorological percentiles. This could be minimising estimated health impacts in analyses of future impacts attributable to heat.

Heat wave characteristics: evaluation of regional climate model performances for Germany

Abstract. Heat waves are among the most severe climate extreme events. In this study, we address the impact of increased model resolution and tailored model settings on the reproduction of these events by evaluating different regional climate model outputs for Germany and its near surroundings between 1980–2009. Outputs of an ensemble of six EURO-CORDEX models with 12.5 km grid resolution and outputs from a high-resolution (5 km) WRF (Weather Research and Forecasting) model run are employed. The latter was especially tailored for the study region regarding the physics configuration. We analyze the reproduction of the maximum temperature, number of heat wave days, heat wave characteristics (frequency, duration and intensity), the 2003 major event, and trends in the annual number of heat waves. E-OBS is used as the reference, and we utilize the Taylor diagram, the Mann–Kendall trend test and the spatial efficiency metric, while the cumulative heat index is used as a measure of intensity. Averaged over the domain, heat waves occurred about 31 times in the study period, with an average duration of 4 d and an average heat excess of 10 ∘C. The maximum temperature was only reproduced satisfactorily by some models. Despite using the same forcing, the models exhibited a large spread in heat wave reproduction. The domain mean conditions for heat wave frequency and duration were captured reasonably well, but the intensity was reproduced weakly. The spread was particularly pronounced for the 2003 event, indicating how difficult it was for the models to reproduce single major events. All models underestimated the spatial extent of the observed increasing trends. WRF generally did not perform significantly better than the other models. We conclude that increasing the model resolution does not add significant value to heat wave simulation if the base resolution is already relatively high. Tailored model settings seem to play a minor role. The sometimes pronounced differences in performance, however, highlight that the choice of model can be crucial.

Evaluating the Present and Future Heat Stress Conditions in the Grand Duchy of Luxembourg

The impact of elevated air temperature and heat stress on human health is a global concern. It not only affects our well-being directly, but also reduces our physical work capacity, leading to negative effects on society and economic productivity. Climate change has already affected the climate in Luxembourg and, based on the results of regional climate models, extreme heat events will become more frequent and intense in the future. To assess historical conditions, the micro-scaleRayManPro 3.1 model was used to simulate the thermal stress levels for different genders and age classes based on hourly input data spanning the last two decades. For the assessment of future conditions, with a special emphasis on heat waves, a multi-model ensemble of regional climate models for different emission scenarios taken from the Coordinated Regional Climate Downscaling Experiment (CORDEX) was used. For both, the past and future conditions in Luxemburg, an increase in the heat stress levels was observed. Small differences for different age groups and genders became obvious. In addition to the increase in the absolute number of heat waves, an intensification of higher temperatures and longer durations were also detected. Although some indications of the adaptation to rising air temperatures can be observed for high-income countries, our results underscore the likelihood of escalating heat-related adverse effects on human health and economic productivity unless more investments are made in research and risk management strategies.

How persistent and hazardous will extreme temperature events become in a warming Portugal?

The impact of rising greenhouse gases (GHGs) in the atmosphere on the temperature distributions is felt not only in the mean values but primarily in the extremes. The temperature distributions are becoming slightly flattened and more broadened towards higher values, leading to a decrease in extreme cold events and more importantly to a considerable increase in the frequency and intensity of extreme hot events. These changes are no longer simple projections but are already occurring. It is thus imperative an assessment of the projected changes even under reduced emissions scenarios for the entire 21st century. In this study, a multi-variable ensemble based on 13 EURO-CORDEX high-resolution simulations at 0.11° resolution, was used to analyse the extreme heat events as well as the Universal Thermal Climate Index (UTCI) for such extremes between March and November over Portugal. The 13 simulations have in common three Representative Concentration Pathways (RCP), RCP2.6, RCP4.5 and RCP8.5 as well as data covering a historical period (1971–2000) and three future consecutive periods, 2011–2040, 2041–2070 and 2071–2 100. The results show that severe future heatwaves will develop beyond the extended summer months in all scenarios. Even under a high mitigation scenario (RCP2.6), the number of heatwaves will more than double in number, relative to the historical record. In the high emission scenario (RCP8.5), a sharp increase in the number, severity and areal extension of heatwaves is projected for the end of the 21st century. The analysis of the heat stress indicates that most of the projected future heatwaves will induce heat stress and the projected increase in areal extension and the number of occurrences will have an impact on morbidity and mortality rates simply due to the shear rise in the number of the affected population and the increased frequency of occurrence.

Parametric heat wave insurance

This paper proposes a flexible framework for structuring and pricing parametric heat wave insurance. The framework is based on a general heat wave definition formulated in terms of an underlying temperature index. The definition can be varied in terms of the heat wave duration, intensity, measurement period and underlying index. This construction makes it straightforward to create contracts tailored to insure against heat events of many different types. A single stochastic model for the underlying index can be used to price all contracts. We consider contracts with payments that depend on the number of heat waves of a certain type occurring in the measurement period and derive the necessary pricing relations based on a general model structure encompassing several popular temperature models in the literature. An empirical case study is performed using data for Berlin where the daily maximum temperature is used as the underlying index. Model implied heat wave probabilities are consistent with historical patterns, point to high likelihoods for short duration heat events of different threshold temperatures and non-negligible risks for future heat waves of extreme temperatures and durations never before observed.

Potential impact of climate change on shifting the calendar of rainfed crops produced in Jordan

Climate change alters the usual pattern of rainfall distribution and temperature in the East Mediterranean region. We investigated the impact of climate change on true season onset, and crop calendar for field crops grown in areas with Semi-Arid-Sub-Humid Mediterranean climate. Analysis showed a clear reduction of annual rainfall for the zone with rainfall more than 200 mm, and above 1°C rise in air temperature for all zones. Generally, the rainfall reduction occurred, in descending order, along the South-North direction. A new approach is proposed to identify the true season onset and the end of the effective rainy season. Shifting the true season onset consequently reduces the crop-growing season and hence the yield. Reducing annual rainfall and the length of effective rainfall season, rising air temperature, and the sharp increase in the number of heat waves will have profound negative impacts on both plant growth and yield.

Spatio-Temporal Analysis of Heatwaves Characteristics in Greece from 1950 to 2020

Heatwave events are of major concern in the global context, since they can significantly impact ecosystems, economies and societies. For this reason, more detailed analyses of the characteristics and trends of heatwaves represent a priority that cannot be neglected. In this study, the interannual and decadal variability of seven indices of heatwaves were investigated during the warmest period of the year (June–August) by using an enhanced resolution reanalysis model (ERA5-Land) over a 71-year period (1950–2020) for the area of Greece. Heatwaves were defined as periods where two thresholds, based on a modified version of the Excess Heat Factor index (EHF) and the 95th percentile of the maximum daily temperature, were exceeded for at least three consecutive days. Greece experiences almost yearly 0.7 heatwaves on average during the whole period of study, while this value has increased by ~80% since 1990. Trend analysis revealed that heatwaves have become more frequent, longer, and more intense since 1950. The percentage of the land area that experiences at least one heatwave per year was almost doubled in the examined period. An increasing trend in the number of heatwaves that occurred in June was identified.

Exacerbated heat in large Canadian cities

Extreme temperature is a major threat to urban populations; thus, it is crucial to understand future changes to plan adaptation and mitigation strategies. We assess historical and CMIP6 projected trends of minimum and maximum temperatures for the 18 most populated Canadian cities. Temperatures increase (on average 0.3°C/decade) in all cities during the historical period (1979–2014), with Prairie cities exhibiting lower rates (0.06°C/decade). Toronto (0.5°C/decade) and Montreal (0.7°C/decade) show high increasing trends in the observation period. Higher-elevation cities, among those with the same population, show slower increasing temperature rates compared to the coastal ones. Projections for cities in the Prairies show 12% more summer days compared to the other regions. The number of heat waves (HWs) increases for all cities, in both the historical and future periods; yet alarming increases are projected for Vancouver, Victoria, and Halifax from no HWs in the historical period to approximately 4 HWs/year on average, towards the end of 2100 for the SSP5–8.5. The cold waves reduce considerably for all cities in the historical period at a rate of 2 CWs/decade on average and are projected to further reduce by 50% compared to the observed period.

Increased occurrence of high impact compound events under climate change

While compound weather and climate events (CEs) can lead to significant socioeconomic consequences, their response to climate change is mostly unexplored. We report the first multi-model assessment of future changes in return periods for the co-occurrence of heatwaves and drought, and extreme winds and precipitation based on the Coupled Model Intercomparison Project (CMIP6) and three emission scenarios. Extreme winds and precipitation CEs occur more frequently in many regions, particularly under higher emissions. Heatwaves and drought occur more frequently everywhere under all emission scenarios examined. For each CMIP6 model, we derive a skill score for simulating CEs. Models with higher skill in simulating historical CEs project smaller increases in the number of heatwaves and drought in Eurasia, but larger numbers of strong winds and heavy precipitation CEs everywhere for all emission scenarios. This result is partly masked if the whole CMIP6 ensemble is used, pointing to the considerable value in further improvements in climate models.

Progress in extreme heat management and warning systems: A systematic review of heat-health action plans (1995-2020)

In recent decades, rising trend in the number of heat waves (HWs) has exacerbated the risk of heat-related mortality and morbidity. The frequent deadly HWs precipitated a multitude of national and sub-national heat-health prevention and research efforts. In 2008, the WHO Regional Office for Europe developed and published guidance on heat-health action plans (HHAPs). This provided a blueprint for countries to design heat-related prevention efforts. Since then, a large corpus of new evidences and implementation experiences has emerged around adaptive measures, alert systems and urban planning interventions. The present study conducts a systematic review to critically assess the advent and development of HHAPs with a special focus on its integration with urban planning policies. It reviews the concept of threshold, indicators for heat event determination and measurement of HWs to understand trigger setting mechanisms. The results show that implementation of core elements of HHAPs varies significantly in the areas of long-term urban planning, real-time surveillance, monitoring and evaluation. Moreover, low levels of inclusion of HHAPs with national policies hinder the overall potential of adaptation measures. The growing impacts of HWs emphasize the urgent need to address spatial heat vulnerability and build urban heat resilience into implementable action plans.

The influence of summer temperatures on the incidence of Takotsubo cardiomyopathy : a retrospective study

Takotsubo cardiomyopathy (TK-CM) is a reversible acute left ventricular dysfunction that cannot be explained by an obstructive coronary lesion. The aim of our study was to explore the possible correlation between the incidence of TK-CM in summer and the average temperature, number of heat waves or number of days hotter than 30°C. 482 patients presented an acute coronary syndrome in the summers of 2012 until 2017 in our region. 15 patients met the inclusion and exclusion criteria and were diagnosed as TK-CM. The study analysis showed a statistically correlation between the number of heatwaves and the incidence of TK-CM (coefficient of correlation: 0.77; p = 0.04). This comforts the hypothesis of climatic influence on this pathology.

Features of the dynamics of heat waves in selected cities of Ukraine

Formulation of the problem. One of the main manifestations of regional climate changes in Ukraine on the background of global warming is substantial rise of air temperature and increasing of extreme weather conditions. Therefore heat waves became a concern. Detection of heat waves and their physical and statistical characteristics on the territory of Ukraine was done by many researchers only during warm period of the year and on the basis of fact data. But it's interesting to find out what happens in this context during cold period as well because heat waves affect not only human health but also agriculture, transportation etc throughout the year. Besides in order to overcome negative consequences and for adaptation of people for climate changes prognostic values of meteorological indices, in particular air temperature according to modern climate change scenarios. Review of previous publications. Consequences of thermal waves impact on population health is being studied in different countries of the world and in the main medical data base PubMed there are more than 1000 publications in this branch of research. But still there is no universal definition of heat waves which could be used as criteria for detecting this anomaly in all the researches. This can be explained that depending on challenges of scientific research or practical service of household activity waves of certain intensity or duration can be the most interesting. Purpose. The aim of this work is detection of heat waves on the basis of actual and scenario data and analysis of their physical and statistical characteristics and dynamics until 2050. Methods. Heat waves were detected on the base of actual data and model ranges by low (RCP 2.6), medium (RCP 4.5), high (RCP 8.5) levels of greenhouse gases emissions and also there were analyzed their physical and statistical characteristics and dynamics until 2050 in different regions of Ukraine. Results. The smallest annual number of heat waves is recorded in the south of Ukraine and the maximum heat wave duration is approximately the same at all the research stations (Uzhgorod, Kharkiv, Odessa). According to all climate change trends that were used, the greatest number of heat waves in the next thirty years is expected in the south of Ukraine, with a maximum in the cold season (October-April). The intensity of heat waves, expressed by the cumulative temperature, during the cold period slightly exceeds this index during the warm period in the west and north-east and substantially exceeds it in the south, and heat waves of the same duration can have quite different intensities. Conclusions. In the west of Ukraine, there is a trend of increasing the number of heat waves and their duration over the studied period by decades, in the northeast and south - these indicators have fluctuated. It was discovered that in all regions, according to actual data, heat waves of 6-9 days have the highest recurrence (82% of total amount of heat waves per year); according to the RCP2.6 scenario, their recurrence will be minimized (up to 52%) in the south of the country. According to all used climate change trends by 2050, the highest number of heat waves is expected in southern Ukraine, with a maximum during the cold season (October-April). The intensity of heat waves of the cold period is higher than during the warm period in all regions of Ukraine, especially the south.

Prediction of Heatwave 2013 over Andhra Pradesh and Telangana, India using WRF Model

Heatwaves are acknowledged to be the major meteorological disaster, causing a noticeable impact on humans and animals’ lives during the last few decades. The number, frequency, duration, intensity, and areal extent of the heatwaves are on the rise during recent years. The Maximum temperature data of 2013 is analyzed to assess the synoptic nature, intensity, frequency, and various significant facets of the heatwave over the south peninsular states of Andhra Pradesh and Telangana. Indian subcontinent experienced a major heatwave during 2013, which claimed 1216 human lives. Even though the highest intensity of maximum temperatures is observed in May over major areas of India, the increasing (incidence, duration, number of spells, and the sweltering temperatures) number of heatwaves are observed over many parts of the country. The northwest and southeast coastal regions are the two heat wave prone regions. The advection of heat from the northwest with the aid of north-westerly winds causes heatwaves over northwest India to sweep or move towards India’s southeast and east coast. The heatwave record over south-eastern India, i.e, Andhra Pradesh and the adjoining Telangana state during May 22–24, 2013 were described in this study. Maximum temperatures above 40°C are observed with a sudden rise by 6 to 7°C over the study region. An attempt is made to predict the maximum temperatures 72 hours before the existence of a heatwave at 3 km horizontal resolution using the Advanced core of the Weather Research and Forecasting (WRF) model. Model predicted temperature values match with observations and the statistical metrics show a high index of the agreement, lower values for root-mean-square error and mean absolute error. Atmospheric circulation patterns associated with this heatwave are also presented. The arrest of sea breeze, the hovering of diabatic heat because of subsidence is the factor that abetted the heatwave blockade over the south-eastern part of the country. The WRF model forecasts could present the occurance of the heat wave over AP and Telangana region with 72 hour lead time with high accuracy.

Dynamics thresholds for heat-health watch and warning system with extended season

BACKGROUND AND AIM: A significant number of heat waves with very severe impacts have been observed over the past three decades. The multiplication of the latter during the last decades has incited some countries to elaborate heat-health watch and warning systems (HHWWS). However, these HHWWS cover the hottest months of the year with a unique threshold for the whole summer season. According to some studies, the summers are expected to be longer and hotter in a future climate, with periods of heat waves earlier and later in the season. Besides, the heat effects tend to be more severe when the human body is not acclimatized to hot temperatures. To adapt the system to potential heat waves outside the hot season and consider the meteorological variability within the season, this study proposes a HHWWS with an extended season and evolving thresholds per month. METHODS: For this, historical health and weather data over the years of Greater Montreal area (Canada) are considered. Splines and distributed lag non-linear model (DLNM) were also used in our approach to the implementation of the system. RESULTS:The resulting HHWWS provide thresholds for a couple of maximum and minimum temperature (in °C) that range from (23 and 12) in April, to (32 and 21) in July and back to (25 and 13) in October. CONCLUSIONS:The proposed system is more flexible and adapted over an extended season and with monthly evolving thresholds. KEYWORDS: Warning systems,Temperature extremes, Environmental epidemiology, climate, thresholds, mortality.

Responses of Manduca sexta larvae to heat waves.

Climate change is increasing the frequency of heat waves and other extreme weather events experienced by organisms. How does the number and developmental timing of heat waves affect survival, growth and development of insects? Do heat waves early in development alter performance later in development? We addressed these questions using experimental heat waves with larvae of the tobacco hornworm, Manduca sexta. The experiments used diurnally fluctuating temperature treatments differing in the number (0-3) and developmental timing (early, middle and/or late in larval development) of heat waves, in which a single heat wave involved three consecutive days with a daily maximum temperature of 42°C. Survival to pupation declined with increasing number of heat waves. Multiple (but not single) heat waves significantly reduced development time and pupal mass; the best models for the data indicated that both the number and developmental timing of heat waves affected performance. In addition, heat waves earlier in development significantly reduced growth and development rates later in larval development. Our results illustrate how the frequency and developmental timing of sublethal heat waves can have important consequences for life history traits in insects.

Health Risks Due To Climate Change: Inequity In Causes And Consequences.

Climate change has altered global to local weather patterns and increased sea levels, and it will continue to do so. Average temperatures, precipitation amounts, and other variables such as humidity levels are all rising. In addition, weather variability is increasing, causing, for example, a greater number of heat waves, many of which are more intense and last longer, and more floods and droughts. These changes are collectively increasing the number of injuries, illnesses, and deaths from a wide range of climate-sensitive health outcomes. Future health risks will be determined not just by the hazards created by a changing climate but also by the sensitivity of individuals and communities exposed to these hazards and the capacity of health systems to prepare for and effectively manage the attendant risks. These risks include deaths and injuries from extreme events (for example, heat waves, storms, and floods), infectious diseases (including food-, water-, and vectorborne illnesses), and food and water insecurity. These risks are unevenly distributed and both create new inequities and exacerbate those that already exist. Most of these risks are projected to increase with each additional unit of warming. Using an equity lens to move beyond incremental to transformational resilience would reduce vulnerability and improve sustainability for all, but substantial additional funding is required for proactive and effective actions by the health system.

Comparing interannual variability in three regional single-model initial-condition large ensembles (SMILEs) over Europe

Abstract. For sectors like agriculture, hydrology and ecology, increasing interannual variability (IAV) can have larger impacts than changes in the mean state, whereas decreasing IAV in winter implies that the coldest seasons warm more than the mean. IAV is difficult to reliably quantify in single realizations of climate (observations and single-model realizations) as they are too short, and represent a combination of external forcing and IAV. Single-model initial-condition large ensembles (SMILEs) are powerful tools to overcome this problem, as they provide many realizations of past and future climate and thus a larger sample size to robustly evaluate and quantify changes in IAV. We use three SMILE-based regional climate models (CanESM-CRCM, ECEARTH-RACMO and CESM-CCLM) to investigate downscaled changes in IAV of summer and winter temperature and precipitation, the number of heat waves, and the maximum length of dry periods over Europe. An evaluation against the observational data set E-OBS reveals that all models reproduce observational IAV reasonably well, although both under- and overestimation of observational IAV occur in all models in a few cases. We further demonstrate that SMILEs are essential to robustly quantify changes in IAV since some individual realizations show significant IAV changes, whereas others do not. Thus, a large sample size, i.e., information from all members of SMILEs, is needed to robustly quantify the significance of IAV changes. Projected IAV changes in temperature over Europe are in line with existing literature: increasing variability in summer and stable to decreasing variability in winter. Here, we further show that summer and winter precipitation, as well as the two summer extreme indicators mostly also show these seasonal changes.

Intraurban social risk and mortality patterns during extreme heat events: A case study of Moscow, 2010-2017.

There is currently an increase in the number of heat waves occurring worldwide. Moscow experienced the effects of an extreme heat wave in 2010, which resulted in more than 10,000 extra deaths and significant economic damage. This study conducted a comprehensive assessment of the social risks existing during the occurrence of heat waves and allowed us to identify the spatial heterogeneity of the city in terms of thermal risk and the consequences for public health. Using a detailed simulation of the meteorological regime based on the COSMO-CLM regional climate model and the physiologically equivalent temperature (PET), a spatial assessment of thermal stress in the summer of 2010 was carried out. Based on statistical data, the components of social risk (vulnerabilities and adaptive capacity of the population) were calculated and mapped. We also performed an analysis of their changes in 2010-2017. A significant differentiation of the territory of Moscow has been revealed in terms of the thermal stress and vulnerability of the population to heat waves. The spatial pattern of thermal stress agrees quite well with the excess deaths observed during the period from July to August 2010. The identified negative trend of increasing vulnerability of the population has grown in most districts of Moscow. The adaptive capacity has been reduced in most of Moscow. The growth of adaptive capacity mainly affects the most prosperous areas of the city.

Change in the heatwave statistical characteristics over China during the climate warming slowdown

Heatwaves are multi-day periods of extremely high-temperature weather relative to a region's average conditions and are among the deadliest natural disasters. This study was designed to evaluate changes in the characteristics of heatwaves during the periods of warming acceleration versus warming slowdown using the multivariate joint probability distributions of heatwave duration and severity. The results revealed that: (1) From the warming acceleration period (1961–1997) to the warming slowdown period (1998–2017), the return levels of heatwave duration increased by <1.0 d as the return period increased. As the return period lengthened, the return level of heatwave severity rose as well; (2) The joint occurrence probability of heatwaves with both variables exceeding the 20-yr, 50-yr, and 100-yr return levels exhibited relative increases of 3%, 8%, and 16% across China, respectively. There were greater than the joint probability of heatwaves with only 1 variable exceeding the return levels; (3) The number of heatwaves with both duration and severity exceeding the 50-yr joint return period increased in China, and this increase was dominated by heatwaves with joint return periods of 50–100 years, leading to a strengthening of heatwave severity.