Changes In Heat Wave Characteristics Research Articles

A study on the monitoring of heatwaves and bivariate frequency analysis based on mortality risk assessment in Wuhan, China.

The increasingly frequent occurrence of urban heatwaves has become a significant threat to human health. To quantitatively analyze changes in heatwave characteristics and to investigate the return periods of future heatwaves in Wuhan City, China, this study extracted 9 heatwave definitions and divided them into 3 mortality risk levels to identify and analyze historical observations and future projections of heatwaves. The copula functions were employed to derive the joint distribution of heatwave severity and duration and to analyze the co-occurrence return periods. The results demonstrate the following. (1) As the concentration of greenhouse gas emissions increases, the severity of heatwaves intensifies, and the occurrence of heatwaves increases significantly; moreover, a longer duration of heatwaves correlated with higher risk levels in each emission scenario. (2) Increasing concentrations of greenhouse gas emissions result in significantly shorter heatwave co-occurrence return periods at each level of risk. (3) In the 3 risk levels under each emission scenario, the co-occurrence return periods for heatwaves become longer as heatwave severity intensifies and duration increases. Under the influence of climate change, regional-specific early warning systems for heatwaves are necessary and crucial for policymakers to reduce heat-related mortality risks in the population, especially among vulnerable groups.

Observed Global Changes in Sector‐Relevant Climate Extremes Indices—An Extension to HadEX3

AbstractGlobal gridded data sets of observed extremes indices underpin assessments of changes in climate extremes. However, similar efforts to enable the assessment of indices relevant to different sectors of society have been missing. Here we present a data set of sector‐specific indices, based on daily station data, that extends the HadEX3 data set of climate extremes indices. These additional indices, which can be used singly or in combinations, have been recommended by the World Meteorological Organization and are intended to empower decision makers in different sectors with accurate historical information about how sector‐relevant measures of the climate are changing, especially in regions where in situ daily temperature and rainfall data are hard to come by. The annual and/or monthly indices have been interpolated on to a 1.875° × 1.25° longitude‐latitude grid for 1901–2018. We show changes in globally‐averaged time series of these indices in comparison with reanalysis products. Changes in temperature‐based indices are consistent with global scale warming, with days with Tmax > 30°C (TXge30) increasing virtually everywhere with potential impacts on crop fertility. At the other end of the scale, the number of days with Tmin < −2°C (TNltm2) are reducing, decreasing potential damage from frosts. Changes in heat wave characteristics show increases in the number, duration and intensity of these extreme events in most places. The gridded netCDF files and, where possible, the underlying station indices are available from https://www.metoffice.gov.uk/hadobs/hadex3 and https://www.climdex.org.

Future Projections of Heat Waves and Associated Mortality Risk in a Coastal Mediterranean City

Climate change has been linked to the escalating frequency, duration, and intensity of heat waves in the Mediterranean region, intensifying health concerns for the general populace. Urban environments face elevated health risks due to concentrated populations and the urban heat island effect, further amplifying nighttime heat conditions. This study aims to project changes in heat wave characteristics and the associated population exposure risk in a large Mediterranean city, Thessaloniki, Greece. High-resolution climate simulations, using the WRF model, were conducted for three 5-year periods (2006–2010, 2046–2050, 2096–2100) under the RCP8.5 emission scenario, covering Thessaloniki with a 2 km grid. By the end of the century, Thessaloniki is projected to experience over 60 annual heat wave days, compared to ~8 in the present climate, while some episodes were found to persist beyond 30 days. The relative risk during heat wave days is expected to rise, which is primarily due to nighttime heat stress. Interestingly, the results indicate that minimum apparent temperature might be a more reliable indicator in predicting heat-related mortality compared to maximum apparent temperature. These findings emphasize the growing importance of informed heat mitigation and adaptation strategies and healthcare preparedness in urban areas facing escalating heat-related health challenges.

Frequency dominates intensity of future heat waves over India

Future changes in heat wave characteristics over India have been analyzed using Coordinated Regional Climate Downscaling Experiments (CORDEX) for South Asia (SA) regional climate model simulations for mid-term (2041-2060) and long-term (2081-2099) future under the representative concentration pathway (RCP) 4.5 and RCP 8.5 emission scenarios, respectively. SMHI_CSIRO-MK3.6 was found to be the best model in simulating heat wave trend over India for historical period. Future projections show a four-to-seven-fold increase in heat wave frequency for mid-term and long-term future under RCP 4.5 scenario, and five-to-ten-fold increase under RCP 8.5 scenario with increase in frequency dominating intensity in both the scenarios. Northwestern, Central, and South-central India emerged as future heat wave hotspots with largest increase in the south-central region. This high-resolution regional future projection of heat wave occurrence will serve as a baseline for developing transformational heat-resilient policies and adaptation measures to reduce potential impact on human health, agriculture, and infrastructure.

Projected changes in heat wave characteristics over India

Projected changes in heat wave characteristics over India

Indian heatwaves in a future climate with varying hazard thresholds

India has experienced remarkable changes in temperature extremes in recent decades due to rapid global warming leading to extreme heat events with disastrous societal impacts. In response to continuing global warming, this study investigates summertime (March–June) heatwave characteristics over India in the present and future climate. During 1951–2020, India Meteorological Department observational data show rising trends in heatwave characteristics such as frequency, intensity, duration, and season length, mainly over India’s northwest, central, and south peninsular regions. Further, the present study explores the changes in future heatwave characteristics using the state-of-the-art statistically downscaled bias-corrected climate models data from Coupled Model Intercomparison Project Phase 6 (CMIP6) of the Shared Socioeconomic Pathway scenario. This study uses varying hazard thresholds, namely fixed (time-invariant historical climatological threshold) and decadal moving thresholds (time-varying future climatological threshold), to define heatwaves and examine the future changes in heatwave characteristics over India. Results show a significant increase in mean summertime heatwaves defined using fixed thresholds in terms of their frequency, duration, number, amplitude, cumulative magnitude, and season length in the near future (NF) (2025–2054) and the far future (FF) (2065–2094) compared to the baseline period (1985–2014) over much of India, with the most substantial increases seen in the FF. However, heatwaves defined using the decadal moving thresholds show no significant changes in their characteristics during the NF but a substantial change in the FF over many parts of India. This work is the first attempt to use bias-corrected CMIP6 models data to project heatwave characteristics utilising the concept of the varying hazard thresholds across India. Overall, this study provides a comprehensive assessment of climate change’s impact on Indian heatwaves, which can help in planning better adaptation and mitigation strategies.

European heatwaves in present and future climate simulations: a Lagrangian analysis

Abstract. Heatwaves are prolonged periods of anomalously high temperatures that can have devastating impacts on the environment, society and economy. In recent history, heatwaves have become more intense and more numerous over most continental areas, and it is expected that this trend will continue due to the ongoing global temperature rise. This general intensification may be modified by changes also in the underlying thermodynamical and dynamical processes. In order to study potential changes in heatwave characteristics and dynamics, we compare Lagrangian backward trajectories of airstreams associated with historic (1991–2000) and future (2091–2100) heatwaves in six different European regions. We use a percentile-based method (Heat Wave Magnitude Index daily) to identify heatwaves in a large ensemble of climate simulations (Community Earth System Model Large Ensemble (CESM-LE) with 35 members). The simulations have been forced by historical representative concentration pathways (RCPs) up to 2005 and by the RCP8.5 scenario afterwards. In general, we find that air parcels associated with heatwaves are located to the east or inside the respective regions 3 d prior to the events. For future heatwaves, the model projects a north-/northeastward shift of the origin of the air masses in most study regions. Compared to climatological values, airstreams associated with heatwaves show a larger temperature increase along their trajectory, which is connected to stronger descent and/or stronger diabatic heating when the air parcels enter the boundary layer. We find stronger descent associated with adiabatic warming in the northern, more continental regions and increased diabatic heating in all regions (except of the British Isles) in the simulated future climate. The enhanced diabatic heating is even more pronounced for heatwaves over continental regions. Diabatic temperature changes of near-surface air are driven by sensible heat fluxes, which are stronger over dry soils. The amplified diabatic heating associated with future heatwaves may thus be explained by an additional drying of the land surface.

Future changes in heat wave characteristics and their impacts on the electricity demand in South Korea

This study examined the characteristics of the extreme high temperature events in South Korea in relation to the spatial extent, intensity, and persistence of the heat wave (HW), and analyzed the effect of the HW events on the future changes in electricity demands. The HW magnitude is newly calculated by combining the spatial extent of HW with its station average intensity, to evaluate the effect of extreme high temperatures more accurately. The observed frequency and magnitude of heat wave days (HWDs) have significantly increased during 1973–2019. Climate model simulations under the Representative Concentration Pathways (RCP) 8.5 scenario project the increased occurrences of unprecedented wide and strong HW events in the late 21st century (2071–2100). Observations show that the electricity demands increase as the spatial extent of HW widens, the intensity gets stronger, and the duration gets longer. Based on the observed relationship, we proposed a multiple linear regression model to predict the electricity demand with improved accuracy by including the magnitude and duration of HWs as additional explanatory factors. According to the proposed model, as the magnitude and the duration of HWs increase in the future, electricity demands required for cooling are predicted to increase significantly. In the late 21st century, the daily peak electricity demands on HWDs are projected to increase by 9.1% relative to the present level. In particular, its extreme values (30-year return level) are expected to increase more strongly by 19.1%, which is found to be alleviated substantially (4.6%) when greenhouse gas emission is reduced following the RCP 2.6 scenario. Further, strong electricity demands are expected to expand into early and late summer, irrespective of scenarios, in line with the summer season expansion. These climate-induced increases in energy demands will significantly amplify those due to the socioeconomic growth.

Rapid rises in the magnitude and risk of extreme regional heat wave events in China

Increasing occurrence of extreme heat waves poses serious risks to human society and ecosystems. Past studies generally examined the changes in heat wave characteristics at individual stations or grid points; however, a heat wave typically appears as a regional event being continuous in time and space. Using an objective identification technique for distinguishing regional extreme events and a metric for measuring regional heat wave magnitude (i.e., an integrated index that accounts for heat wave intensity, duration, and spatial extent), this study revealed an approximate doubling in both the frequency and the magnitude of regional heat wave events observed over 1960–2018 in China. The identified top three regional heat wave events occurred in the summers of 2013, 2017, and 2003, respectively. Fine-resolution multimodel climate projections suggest that China will experience regional heat wave events with magnitude exceeding the 2013 heat event on a regular basis by 2030 under a business-as-usual scenario (RCP8.5). Compared to a 2 °C warming level, 1.5 °C warming could halve the expected occurrence of future severe regional heat wave events with magnitude similar to or slightly greater than the record-breaking one in 2013.

Heatwaves in Southeast Asia and Their Changes in a Warmer World

AbstractBased on the observational dataset SA‐OBS and model outputs from the Community Earth System Model Large Ensemble project, this study investigates heatwaves in Southeast Asia in the current and future warmer climate. A heatwave is detected when the daily maximum temperature exceeds the 90th percentile threshold at each grid for at least three consecutive days. Three characteristics describing the frequency, duration, and amplitude of heatwaves are examined, including the sum of heatwave days per year (HWF) satisfying the heatwave definition, the length of the longest yearly heatwave event (HWD), and the hottest amplitude of the hottest yearly heatwave event (HWA). Results indicate that increased global warming is associated with substantial changes in heatwave characteristics over Southeast Asia, with more frequent heatwaves, longer heatwave duration, and higher extreme temperatures. The increase in HWA has a linear growth against global warming levels with distinct regional differences between the Maritime Continent and the Indochina Peninsula due to their different heat content of lower atmospheric boundaries. In contrast, those in HWF and HWD have nonlinear growth characteristics. The projected warmer future tends to be associated with a higher risk ratio value with the occurrence of rarer extreme heatwaves relative to the current climate. These results reiterate the potential risks of extreme regional heatwaves if global warming is unrestricted.

Recent changes in heatwave characteristics over Korea

Global warming and abnormal climate change have resulted in an increase in the frequency of severe heatwave events. Recently, a series of extreme heatwave events have occurred in South Korea, and the damage from these events has also been increasing. Thus, it is necessary to analyze the mechanisms for generating and developing heatwaves. In this study, the long-term trend for heatwave events in South Korea was investigated using cluster analysis. Heatwave events in a 38-year period in South Korea were defined, and their synoptic patterns were categorized into three clusters. The number of heatwave days of cluster 2, which is related to the anomalous positive geopotential height (GPH) over the Kamchatka Peninsula, was found to significantly increase in recent years (2000–2018) compared with the past (1981–1999). In contrast, the frequency of cluster 3 associated with a negative GPH anomaly over the Kamchatka Peninsula decreased in the same period. There were five regions, including northern China and the Kamchatka Peninsula, where the mid-level GPH significantly increased between 2000 and 2018. This change in GPH was positively (negatively) correlated with the patterns associated to long-term variability of heatwave days of cluster 2 (cluster 3). The long-term trends of the GPH anomalies over five regions showed a significant correlation with the North Atlantic Oscillation (NAO) index during midsummer. As a result, it is likely that the heatwave events related to cluster 2 (cluster 3) have increased (decreased) in South Korea because the long-term variability of the summer NAO has recently induced a favorable (unfavorable) atmospheric condition for cluster 2 (cluster 3).

Heatwaves intensification in Australia: A consistent trajectory across past, present and future

Heatwaves are defined as unusually high temperature events that occur for at least three consecutive days with major impacts to human health, economy, agriculture and ecosystems. This paper investigates: 1) changes in heatwave characteristics such as peak temperature, number of events, frequency and duration over a past 67-year period in Australia; 2) projected changes in heatwave characteristics for this century in Queensland, northeast Australia; and 3) the avoided heatwave impacts of limiting global warming by 1.5 °C, 2.0 °C and 3.0 °C. The results reveal that heatwaves have increased in intensity, frequency and duration across Australia over the past 67 years, such intensification was particularly higher on recent decades. Downscaled future climate projections for Queensland suggest that heatwaves will further intensify over the current century. The projections also highlight that distinct climatic regions within Queensland may have different heatwave responses under global warming, where tropical and equatorial heatwaves appear to be more sensitive to elevated atmospheric CO2 concentrations than temperate and arid regions. The results offer new insights to support climate adaptation and mitigation at regional scales. These findings are already being used by health and emergency services to inform the development of statewide policies to mitigate heatwave impacts.

Projected changes in heat wave characteristics in the Carpathian Basin comparing different definitions

Heat waves (HWs) associated with climate change and increased near-surface air temperature can be considered as a climatic hazard for people and the environment. This study evaluates six HW detecting methods and the estimated HW characteristics (duration, frequency and intensity) from observational (CarpatClim database) and modelled (RegCM simulations with the representative concentration pathway (RCP) 4.5 and 8.5) datasets. The RegCM model results show a considerable future increase (by 2016-2045; 2061-2090) in HW days compared to the reference period (1971-2000). In case of RCP4.5, HW days become 3-6 times more frequent, while the increase is 5-9 fold for RCP8.5 by the end of the century. As a consequence of climate change, HW durations are also projected to become 1-2 (3-4) days longer on average for RCP4.5 (RCP8.5) in the Carpathian Basin.

Projected changes in heat wave characteristics in the Carpathian Basin comparing different definitions

Heat waves (HWs) associated with climate change and increased near-surface air temperature can be considered as a climatic hazard for people and the environment. This study evaluates six HW detecting methods and the estimated HW characteristics (duration, frequency and intensity) from observational (CarpatClim database) and modelled (RegCM simulations with the representative concentration pathway (RCP) 4.5 and 8.5) datasets. The RegCM model results show a considerable future increase (by 2016-2045; 2061-2090) in HW days compared to the reference period (1971-2000). In case of RCP4.5, HW days become 3-6 times more frequent, while the increase is 5-9 fold for RCP8.5 by the end of the century. As a consequence of climate change, HW durations are also projected to become 1-2 (3-4) days longer on average for RCP4.5 (RCP8.5) in the Carpathian Basin.

Recent Changes in U.S. Regional Heat Wave Characteristics in Observations and Reanalyses

AbstractHumidity is a key determinant of heat wave impacts, but studies investigating changes in extreme heat events have not differentiated between events characterized by high temperatures and those characterized by simultaneously elevated temperature and humidity. The authors present a framework, using air temperature (T) and equivalent temperature (TE; a measure combining temperature and specific humidity), to examine changes in local percentile-based extreme heat events characterized by high temperature (T only) and those with high temperature and humidity (T-and-TE events). Application to one observational dataset (PRISM), four reanalysis products (1981–2015), and seven U.S. regions reveals widespread changes in heat wave characteristics over the 35-yr period. Agreement among the datasets employed on several heat wave metrics suggests that many of the findings are robust. With the exception of the northern plains region, all regions experienced increases in both T-only and T-and-TE heat wave day (HWD) frequency in each of the reanalyses. In the northern plains, all datasets have negative trends in T-only HWD frequency and positive trends in T-and-TE HWD frequency. Trends in HWD frequency were generally accompanied by changes in the spatial footprint in heat wave conditions. Temperature has increased significantly during T-only HWDs in the western regions, while increases in TE during T-and-TE HWDs have occurred in the central United States and Northeast region. These findings suggest that equivalent temperature provides an alternative perspective on the evolution of regional heat wave climatology. Studies considering changes in regional heat wave impacts should carefully consider the role of atmospheric moisture.

Changes in heat wave characteristics over Extremadura (SW Spain)

Heat wave (HW) events are becoming more frequent, and they have important consequences because of the negative effects they can have not only on the human population in health terms but also on biodiversity and agriculture. This motivated a study of the trends in HW events over Extremadura, a region in the southwest of Spain, with much of its area in summer devoted to the production of irrigated crops such as maize and tomatoes. Heat waves were defined for the study as two consecutive days with temperatures above the 95th percentile of the summer (June–August) maximum temperature (T max) time series. Two datasets were used: One consisted of 13 daily temperature records uniformly distributed over the Region, and the other was the SPAIN02 gridded observational dataset, extracting just the points corresponding to Extremadura. The trends studied were in the duration, intensity and frequency of HW events, and in other parameters such as the mean, low (25th percentile) and high (75th percentile) values. In general terms, the results showed significant positive trends in those parameters over the east, the northwest and a small area in the south of the region. In order to study changes in HW characteristics (duration, frequency and intensity) considering different subperiods, a stochastic model was used to generate 1000 time series equivalent to the observed ones. The results showed that there were no significant changes in HW duration in the last 10-year subperiod in comparison with the first. But, the results were different for warm events (WE), defined with a lower threshold (the 75th percentile), which are also important for agriculture. For several sites, there were significant changes in WE duration, frequency and intensity.

The representation of health‐relevant heatwave characteristics in a Regional Climate Model ensemble for New South Wales and the Australian Capital Territory, Australia

ABSTRACTHeatwaves have been linked to increased rates of human mortality and morbidity. Given these adverse health impacts, it is crucial to improve our understanding of future changes in these extreme events to inform health impacts studies and adaptation planning. While this information would be most beneficial at a local scale, Global Climate Models provide projections on much coarser resolutions. Regional Climate Models, such as those used in the New South Wales/Australian Capital Territory Regional Climate Modelling (NARCliM) project, provide simulations at a finer scale more appropriate for regional assessments. This study uses NARCliM output to investigate the ability of a Regional Climate Model ensemble to represent heatwave characteristics through the Excess Heat Factor, an index that includes factors that are known to be important to the heat‐health relationship. Both uncorrected and bias‐corrected model output is evaluated against observationally‐derived heatwave characteristics for the period 1990–2009. The effect of bias‐correction on future changes in heatwave characteristics is also assessed. Overall, the simulations provided a good representation of the recent climate and bias‐correction did not greatly change simulated heatwave characteristics. Some regions were more affected by bias‐correction than others, with bias‐correction being most beneficial for coastal regions. We emphasise that these results may not apply to all indices measuring extreme heat, and demonstrate that results for an index based on a fixed absolute temperature threshold are substantially affected when bias‐correction is applied. While supporting bias‐correction, this study demonstrates that it is not necessarily required when evaluating a relative measure such as the Excess Heat Factor.

Projected changes in heat wave characteristics in the eastern Mediterranean and the Middle East

According to observed twentieth century temperature trends and twenty-first century climate model projections, the region that encompasses the eastern Mediterranean and the Middle East (EMME) is identified as a climate change hot spot. We extend previous studies by a comprehensive climatology of heat waves in the EMME based on regional climate model simulations for the recent past and the end of the twenty-first century. A percentile-based definition of heat waves is used to account for local climatic conditions. Spatial patterns of several heat wave properties are assessed and associated with atmospheric circulation regimes over specific locations. To cover a range of possible future climates, we use three SRES emission scenarios. According to our results, all indices that characterize heat wave severity will strongly increase compared with the control period of 1961–1990. The northern part of the EMME could be exposed to increased heat wave amplitudes by 6–10 °C, and the southern part may experience 2–3 months more combined hot days and tropical nights. Heat wave peak temperatures will be higher due to the overall mean warming as well as stronger summer anticyclonic conditions. The projected changes will affect human health and the environment in multiple ways and call for impact studies to support the development of adaptation strategies.

Increased risk of heat waves in Florida: Characterizing changes in bivariate heat wave risk using extreme value analysis

Maximum and minimum daily temperatures from the second half of the 20th century are examined using a high resolution dataset of 833 grid cells across the state of Florida. A bivariate Extreme Value Analysis Point Process approach is used to model characteristics including the frequency, magnitude, duration, and timing of periods or heat waves during which both daily maximum and minimum temperatures exceed their respective 90th percentile thresholds. Variability in heat wave characteristics is examined across the state to give an indication of those areas where heat waves with certain characteristics may be more likely to occur. Changes in heat wave characteristics through time are examined by halving the temperature record and determining changes to heat wave characteristics between the two periods. This exploration of changes in heat wave risk through time gives a possible suggestion of trends in future heat wave risk. Findings indicate that there is considerable spatial variability in heat wave characteristics although heat waves have become increasingly frequent and intense throughout much of the state.

Future projections of heat waves around Japan simulated by CMIP3 and high‐resolution Meteorological Research Institute atmospheric climate models

AbstractFuture changes in heat wave characteristics around Japan are investigated using Coupled Model Intercomparison Project Phase 3 (CMIP3) model outputs, and high‐resolution present‐day (1979–2003) and future (2075–2099) climate simulations under the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) A1B emission scenario. The high‐resolution simulations are conducted using 20, 60, and 180 km mesh atmospheric general circulation models (AGCMs), as well as a 5 km mesh regional climate model (RCM) nested within the 20 km mesh AGCM. The CMIP3 models project that the frequency of heat wave days (HWF) will increase 22.8, 22.3, and 26.5 d yr–1 in northern, eastern, and western Japan, respectively. The multimodel ensemble spread of future changes in HWF averaged around Japan is large (4–58 d yr–1). The spread is affected by the climate sensitivity of the models and the simulated magnitude of the interannual variation of the daily maximum temperature in present‐day climate. In the atmospheric model simulations, the 5 and 20 km mesh models can qualitatively simulate observed HWF distributions, which are affected by steep backbone mountain ranges in Japan. The 5 and 20 km mesh models project large (>30 d yr–1) increases in HWF in the coastal areas of Japan. The duration of heat wave days is projected to increase in areas with increasing HWF.