European Heat Wave Research Articles

Towards a more comprehensive assessment of the intensity of historical European heat waves (1979–2019)

AbstractEurope has been affected by record‐breaking heat waves in recent decades. Using station data and a gridded reanalysis as input, four commonly used heat wave indices, the heat wave magnitude index daily (HWMId), excess heat factor (EHF), wet‐bulb globe temperature (WBGT) and universal thermal climate index (UTCI), are computed. The extremeness of historical European heat waves between 1979 and 2019 using the four indices and different metrics is ranked. A normalisation to enable the comparison between the four indices is introduced. Additionally, a method to quantify the influence of the input parameters on heat wave magnitude is introduced. The spatio‐temporal behaviour of heat waves is assessed by spatial–temporal tracking. The areal extent, large‐scale intensity and duration are visualized using bubble plots. As expected, temperature explains the largest variance in all indices, but humidity is nearly as important in WBGT and wind speed plays a substantial role in UTCI. While the 2010 Russian heat wave is by far the most extreme event in duration and intensity in all normalized indices, the 2018 heat wave was comparable in size for EHF, WBGT and UTCI. Interestingly, the well‐known 2003 central European heat wave was only the fifth and tenth strongest in cumulative intensity in WBGT and UTCI, respectively. The June and July 2019 heat waves were very intense, but short‐lived, thus not belonging to the top heat waves in Europe when duration and areal extent are taken into account. Overall, the proposed normalized indices and the multi‐metric assessment of large‐scale heat waves allow for a more robust description of their extremeness and will be helpful to assess heat waves worldwide and in climate projections.

Accelerated western European heatwave trends linked to more-persistent double jets over Eurasia

Persistent heat extremes can have severe impacts on ecosystems and societies, including excess mortality, wildfires, and harvest failures. Here we identify Europe as a heatwave hotspot, exhibiting upward trends that are three-to-four times faster compared to the rest of the northern midlatitudes over the past 42 years. This accelerated trend is linked to atmospheric dynamical changes via an increase in the frequency and persistence of double jet stream states over Eurasia. We find that double jet occurrences are particularly important for western European heatwaves, explaining up to 35% of temperature variability. The upward trend in the persistence of double jet events explains almost all of the accelerated heatwave trend in western Europe, and about 30% of it over the extended European region. Those findings provide evidence that in addition to thermodynamical drivers, atmospheric dynamical changes have contributed to the increased rate of European heatwaves, with implications for risk management and potential adaptation strategies.

Excess Heat Factor climatology, trends, and exposure across European Functional Urban Areas

In Europe, regional climate change prospects indicate the urgency of adapting to extreme weather events. While increasing temperature trends have already been detected, in the last decades, the adoption of a European heatwave (HW) early-warning index is not yet consensual, partially due to the significant number of alternative algorithms, in some cases adjusted to the measurement of sector-specific impacts (as per the Expert Team on Climate Risk and Sector-specific Indices (ET-SCI)). In particular, the Excess Heat Factor (EHF) has been shown to accurately predict heat-related human health outcomes, in mid-latitude climates, provided that local summer exposure to excess heat is mostly driven by extreme air temperatures, with a lower contribution from relative humidity. Here, annual summaries of EHF-based HW detection were calculated for the European region, using daily maximum and minimum temperatures from the homogenised version of the E-OBS gridded dataset. Annual HW frequencies, duration, mean magnitude, maximum amplitude, and severity were subject to climatology and trend analysis across the European biogeographical regions, considering the 1961–1990 period as the baseline reference for anomaly detection in the more recent (1991–2018) decades. As HW-dependent morbidity/mortality affects mostly the elderly, an EHF-based HW Exposure Index was also calculated, by multiplying the recent probability of severe events per the number of people aged 65, or more, in the European Functional Urban Areas (FUAs). Results show that recent historical EHF-based patterns diverge across European Biogeographical regions, with a clear latitudinal gradient. Both the historical mean and recent trends point towards the greater exposure in the southern European Mediterranean region, driven by the significant increase of HW frequency, duration and maximum severity, especially in the last 3 decades; conversely, annual maximum EHF intensities (i.e., greatest deviations from the local 90th daily mean temperature) are mostly found in the northern and/or high altitude Boreal, Alpine and Continental regions, as a consequence of the latitudinal effect of local climatology on the HWM/HWA indices (this also translates into greater magnitudes of change, in this regions). Nonetheless, by simultaneously considering the probability of Severe HW occurrence in the last three decades, together with the log transformation of people aged 65 or more, results show that greater HW Exposure Indices affect FUAs across the whole Europe, irrespective of its regional climate, suggesting that more meaningful vulnerability assessments, early warning and adaptation measures should be prioritized accordingly.

The negative bidirectional interaction between climate change and the prevalence and care of liver disease: A joint BSG, BASL, EASL, and AASLD commentary

The climate crisis is one of the biggest threats to global health of the 21st century1 because climate change is accompanied by numerous medical consequences.2 We are already seeing these negative global health impacts due to excessive ambient temperatures and air pollution. One notable episode was the extreme heatwave in Europe in summer 2003, which resulted in approximately 70,000 more deaths across Europe, of which 20% in London and 70% in Paris were attributed to human-induced or anthropogenic climate change.

The Negative Bidirectional Interaction Between Climate Change and the Prevalence and Care of Liver Disease: A Joint BSG, BASL, EASL, and AASLD Commentary

The Negative Bidirectional Interaction Between Climate Change and the Prevalence and Care of Liver Disease: A Joint BSG, BASL, EASL, and AASLD Commentary

The July 2019 European Heat Wave in a Warmer Climate: Storyline Scenarios with a Coupled Model Using Spectral Nudging

Abstract Extreme weather events are triggered by atmospheric circulation patterns and shaped by slower components, including soil moisture and sea surface temperature, and by the background climate. This separation of factors is exploited by the storyline approach in which an atmospheric model is nudged toward the observed dynamics using different climate boundary conditions to explore their influence. The storyline approach disregards uncertain climatic changes in the frequency and intensity of dynamical conditions, focusing instead on the thermodynamic influence of climate on extreme events. Here we demonstrate an advanced storyline approach that employs a coupled climate model (AWI-CM-1-1-MR) in which the large-scale free-troposphere dynamics are nudged toward ERA5 data. Five-member ensembles are run for present-day (2017–19), preindustrial, +2-K, and +4-K climates branching off from CMIP6 historical and scenario simulations of the same model. In contrast to previous studies, which employed atmosphere-only models, feedbacks between extreme events and the ocean and sea ice state, and the dependence of such feedbacks on the climate, are consistently simulated. Our setup is capable of reproducing observed anomalies of relevant unconstrained parameters, including near-surface temperature, cloud cover, soil moisture, sea surface temperature, and sea ice concentration. Focusing on the July 2019 European heat wave, we find that the strongest warming amplification expands from southern to central Europe over the course of the twenty-first century. The warming reaches up to 10 K in the 4-K-warmer climate, suggesting that an analogous event would entail peak temperatures around 50°C in central Europe. Significance Statement This work explores a new storyline method to determine the impact of climate change on specific recent extreme events. The observed evolution of the large-scale atmospheric circulation is imposed in a coupled climate model. Variations in climate parameters, including ocean temperatures and sea ice, are well reproduced. By varying the background climate, including CO2 concentrations, it is demonstrated how the July 2019 European heat wave could have evolved in preindustrial times and in warmer climates. For example, up to 10°C warmer peak temperatures could occur in central Europe in a 4°C warmer climate. The method should be explored for other types of extreme events and has the potential to make climate change more tangible and to inform adaptation measures.

The 2018 European heatwave led to stem dehydration but not to consistent growth reductions in forests

Heatwaves exert disproportionately strong and sometimes irreversible impacts on forest ecosystems. These impacts remain poorly understood at the tree and species level and across large spatial scales. Here, we investigate the effects of the record-breaking 2018 European heatwave on tree growth and tree water status using a collection of high-temporal resolution dendrometer data from 21 species across 53 sites. Relative to the two preceding years, annual stem growth was not consistently reduced by the 2018 heatwave but stems experienced twice the temporary shrinkage due to depletion of water reserves. Conifer species were less capable of rehydrating overnight than broadleaves across gradients of soil and atmospheric drought, suggesting less resilience toward transient stress. In particular, Norway spruce and Scots pine experienced extensive stem dehydration. Our high-resolution dendrometer network was suitable to disentangle the effects of a severe heatwave on tree growth and desiccation at large-spatial scales in situ, and provided insights on which species may be more vulnerable to climate extremes.

Heatwave breaks down the linearity between sun-induced fluorescence and gross primary production.

Sun-induced fluorescence in the far-red region (SIF) is increasingly used as a remote and proximal-sensing tool capable of tracking vegetation gross primary production (GPP). However, the use of SIF to probe changes in GPP is challenged during extreme climatic events, such as heatwaves. Here, we examined how the 2018 European heatwave (HW) affected the GPP-SIF relationship in evergreen broadleaved trees with a relatively invariant canopy structure. To do so, we combined canopy-scale SIF measurements, GPP estimated from an eddy covariance tower, and active pulse amplitude modulation fluorescence. The HW caused an inversion of the photosynthesis-fluorescence relationship at both the canopy and leaf scales. The highly nonlinear relationship was strongly shaped by nonphotochemical quenching (NPQ), that is, a dissipation mechanism to protect from the adverse effects of high light intensity. During the extreme heat stress, plants experienced a saturation of NPQ, causing a change in the allocation of energy dissipation pathways towards SIF. Our results show the complex modulation of the NPQ-SIF-GPP relationship at an extreme level of heat stress, which is not completely represented in state-of-the-art coupled radiative transfer and photosynthesis models.

Identifying agricultural disaster risk zones for future climate actions.

Identifying agricultural disaster risk regions before the occurrence of climate-related disasters is critical for early mitigation planning. This paper aims to identify these regions based on data from the Food and Agriculture Organization of the United Nations (FAO), the bilateral and multilateral trade network data of the World Integrated Trade Solution(WITS) and the agent-based economic model Acclimate. By applying a uniform forcing across agricultural sectors of some breadbasket regions (US, EU and China), when single and simultaneous extreme weather events occur, such as the 2018 European heatwave, production and consumption value losses and gains are calculated at regional and global levels. Comparing the FAO data sets, WITS, and Acclimate's production value losses, the results show a strong dependence of agricultural production losses on a region's output and connectivity level in the global supply and trade network. While India, Brazil, Russia, Canada, Australia, and Iran are highly vulnerable, the imposition of export restrictions to compensate for demand shortfalls makes Sub-Saharan Africa the most vulnerable region, as it is heavily dependent on agricultural imports. In addition, simultaneous extreme weather events can exacerbate the loss of value of agricultural production relative to single extreme weather events. Agricultural practices to increase production such as smart farming, increased investment in plantation agriculture, and diversification of trading partners can help mitigate future food security risks in Sub-Saharan Africa and other agricultural import-dependent regions.

Forecast-based attribution of a winter heatwave within the limit of predictability

Attribution of extreme weather events has expanded rapidly as a field over the past decade. However, deficiencies in climate model representation of key dynamical drivers of extreme events have led to some concerns over the robustness of climate model-based attribution studies. It has also been suggested that the unconditioned risk-based approach to event attribution may result in false negative results due to dynamical noise overwhelming any climate change signal. The "storyline" attribution framework, in which the impact of climate change on individual drivers of an extreme event is examined, aims to mitigate these concerns. Here we propose a methodology for attribution of extreme weather events using the operational European Centre for Medium-Range Weather Forecasts (ECMWF) medium-range forecast model that successfully predicted the event. The use of a successful forecast ensures not only that the model is able to accurately represent the event in question, but also that the analysis is unequivocally an attribution of this specific event, rather than a mixture of multiple different events that share some characteristic. Since this attribution methodology is conditioned on the component of the event that was predictable at forecast initialization, we show how adjusting the lead time of the forecast can flexibly set the level of conditioning desired. This flexible adjustment of the conditioning allows us to synthesize between a storyline (highly conditioned) and a risk-based (relatively unconditioned) approach. We demonstrate this forecast-based methodology through a partial attribution of the direct radiative effect of increased CO2 concentrations on the exceptional European winter heatwave of February 2019.

Is it climate change? Coverage by online news sites of the 2019 European summer heatwaves in France, Germany, the Netherlands, and the UK

In 2019, several countries across Western Europe experienced record-breaking temperatures and heatwaves which, in some cases, reached temperatures of over 40 °C for three to four consecutive days during June and July. Extreme event attribution (EEA) studies show that anthropogenic climate change increased the likelihood of these events by at least three to ten times (with different results for different countries), and increased the temperature by 1.2 to 3.0 °C. The heatwaves resulted in more than 2500 deaths. Based on a content analysis of 267 articles taken from 20 of the most visited online news websites in four of the countries most affected by the heatwaves (France, Germany, the Netherlands, and the UK), we find strong variations between countries and media outlets in how much attention journalists pay to links between climate change and the heatwaves (the UK media the most, and politically left-leaning titles more than right-leaning ones); many different types of statements depicting the link but in general, the presence of accurate, science-based descriptions; a strong presence of EEA studies in the coverage; and more quotes from climate scientists than politicians and NGOs, with a minimal presence of climate change skeptics. These results contribute to our understanding of media coverage around extreme weather events in different countries and media outlets, and how such events might serve as opportunities for public engagement with climate change.

Heat strain and mortality effects of prolonged central European heat wave\u2014an example of June 2019 in Poland

The occurrence of long-lasting severe heat stress, such as in July–August 2003, July 2010, or in April–May 2018 has been one of the biggest meteorological threats in Europe in recent years. The paper focuses on the biometeorological and mortality effects of the hot June that was observed in Central Europe in 2019. The basis of the study was hourly and daily Universal Thermal Climate Index (UTCI) values at meteorological stations in Poland for June 2019. The average monthly air temperature and UTCI values from 1951 to 2018 were analysed as background. Grosswetterlagen calendar of atmospheric circulation was used to assess synoptic conditions of heat wave. Several heat strain measures were applied : net heat storage (S), modelled heart rate (HR), sultriness (HSI), and UTCI index. Actual total mortality (TM) and modelled strong heat-related mortality (SHRM) were taken as indicators of biometeorological consequences of the hot June in 2019. The results indicate that prolonged persistence of unusually warm weather in June 2019 was determined by the synoptic conditions occurring over the European region and causing advection of tropical air. They led to the emergence of heat waves causing 10% increase in TM and 5 times bigger SHRM then in preceding 10 years. Such increase in SHRM was an effect of overheating and overload of circulatory system of human organism.

Current and projected regional economic impacts of heatwaves in Europe

Extreme heat undermines the working capacity of individuals, resulting in lower productivity, and thus economic output. Here we analyse the present and future economic damages due to reduced labour productivity caused by extreme heat in Europe. For the analysis of current impacts, we focused on heatwaves occurring in four recent anomalously hot years (2003, 2010, 2015, and 2018) and compared our findings to the historical period 1981–2010. In the selected years, the total estimated damages attributed to heatwaves amounted to 0.3–0.5% of European gross domestic product (GDP). However, the identified losses were largely heterogeneous across space, consistently showing GDP impacts beyond 1% in more vulnerable regions. Future projections indicate that by 2060 impacts might increase in Europe by a factor of almost five compared to the historical period 1981–2010 if no further mitigation or adaptation actions are taken, suggesting the presence of more pronounced effects in the regions where these damages are already acute.

Has the risk of a 1976 north‐west European summer drought and heatwave event increased since the 1970s because of climate change?

AbstractIn the summer of 1976, north‐west Europe experienced an exceptional heatwave and drought, which impacted agriculture and public water supply. This study aims to assess how the likelihood of the event in the present‐day climate has changed since 1976 because of climate change. The analysis focuses on the England and Wales region, which was particularly badly impacted. Three key factors contributing to the extreme summer were identified: the dry preceding winter–spring period, the dry summer and the hot summer. Following the principles of event attribution, three methods are used to evaluate the change in event risk: one using observational data, a second using CMIP5 coupled climate models and a third using HadGEM3‐A atmosphere‐only simulations. This is the first time that this method has been used to evaluate how the risk of a historical extreme event has changed since it originally occurred. The results from the three methods agree qualitatively. The probability of a summer at least as hot as 1976 has increased significantly between the 1970s and the present‐day climate (estimated risk ratios 11 (5–95% confidence interval (CI) [7,14]), 9 (CI [4,28]) and 19 (CI [5,25]) based on the three respective methods). In contrast, no significant change in the probability of an extreme dry winter–spring or an extreme dry summer was found. However, the joint probability of an extreme dry winter–spring followed by an extreme hot summer and the probability of an extreme hot and dry summer have both increased significantly between the 1970s and the present day (estimated risk ratios between 5 and 79, and between 3 and 39, respectively). Water resource systems should therefore be robust enough to cope with more frequent occurrences of summers as extreme as 1976.

Scale-dependent response of the urban heat island to the European heatwave of 2018

Extreme heat continues to be a pressing challenge of the changing climate. The impacts of extreme heat manifest on two different spatio-temporal scales: (1) episodic continent-wide heatwaves (HWs) and (2) the city-scale urban heat island (UHI). As HWs are becoming more frequent, longer, and severe, they pose serious implications of increased public health risks at a city scale, and have adverse impacts on agricultural and terrestrial/aquatic ecosystems on the regional scale. Here we offer a fresh perspective of the HW as a forcing that invokes dynamic, heterogeneous, scale-dependent responses evident in inter and intra-urban heat islets. A numerical simulation of the 2018 European HW including the surface and air temperature-based UHIs of six urban agglomerations, with a high-resolution focus on Paris, serves as our case study. We find that the mean nighttime UHI intensities are reduced for inland cities but increased for coastal cities. Our examination of the heat islets reveals two major findings: (i) the HW homogenizes the intra-urban surface temperatures during the daytime (reduces variance), (ii) the HW impacts are most significant on the scale of large, spatially discontiguous extreme heat islets during nighttime. These results underscore the need to move beyond the prevalent HW-mean UHI intensity characterization and toward intra-urban heat islet analyses that aid targeted mitigation.

Detecting Climate Driven Changes in Chlorophyll-a Using High Frequency Monitoring: The Impact of the 2019 European Heatwave in Three Contrasting Aquatic Systems.

The frequency of heatwave events in Europe is increasing as a result of climate change. This can have implications for the water quality and ecological functioning of aquatic systems. We deployed three spectroradiometer WISPstations at three sites in Europe (Italy, Estonia, and Lithuania/Russia) to measure chlorophyll-a at high frequency. A heatwave in July 2019 occurred with record daily maximum temperatures over 40 °C in parts of Europe. The effects of the resulting storm that ended the heatwave were more discernable than the heatwave itself. Following the storm, chlorophyll-a concentrations increased markedly in two of the lakes and remained high for the duration of the summer while at one site concentrations increased linearly. Heatwaves and subsequent storms appeared to play an important role in structuring the phenology of the primary producers, with wider implications for lake functioning. Chlorophyll-a peaked in early September, after which a wind event dissipated concentrations until calmer conditions returned. Synoptic coordinated high frequency monitoring needs to be advanced in Europe as part of water management policy and to improve knowledge on the implications of climate change. Lakes, as dynamic ecosystems with fast moving species-succession, provide a prism to observe the scale of future change.

Reporting on the 2019 European Heatwaves and Climate Change: Journalists’ Attitudes, Motivations and Role Perceptions

ABSTRACT In summer 2019, several countries in Europe experienced unprecedented heatwaves. Two extreme event attribution (EEA) studies, which assess the role of climate change in extreme weather events, were published at roughly the same time as the heatwaves were taking place (June/August 2019). Building on a prior study of online news media coverage of the heatwaves, this study surveyed journalists from major news outlets in France, Germany, the Netherlands and the UK. Based on the responses of 42 journalists, we found a relative lack of knowledge about EEA studies but a high level of importance assigned to writing about the link between the heatwaves and climate change (e.g., likelihood or intensity); a relatively low number of specialist reporters vs. general reporters covering the heatwaves; a strong reliance on scientific experts as sources; no inclusion of climate change deniers; stronger role perceptions as educators than advocates; relatively little time and resource constraints on their reporting; and an overall tendency for the journalists to report more about climate change. The findings provide new insights into journalism practice and climate journalism in terms of the peculiarities and contextual factors that can influence coverage of extreme weather events and climate change.

SARS COV11 AND OTHER CALAMITIES IN ADAM NEVILL’S LOST GIRL

Speculating about future based on the present, climate change fiction (cli-fi) seems to have proved its unique potential to predict the environmental and social repercussions of the forced anthropogenic transformation(s) on Earth. As a cli-fi and horror novel, it is hardly a coincidence that the British author, Adam Nevill’s Lost Girl (2015) predicts no less with its haunting atmosphere. Envisioning a total collapse of the world through grim depictions of the nonhuman environment and restless societies, it recounts the dangerous quest of a father to find his lost daughter amidst (un)natural disasters, pandemics, and chaos. In the oddly realistic world of Lost Girl, originating from extreme weather conditions and the loss of natural balance, new strains of deadly viruses take hold of the world. Prophesying the coronavirus pandemic and other calamities that actually came out to be true five years later, in 2020; such as the destructive wildfires in Australia or the heatwaves in Europe among others, Lost Girl is a noteworthy cli-fi novel with its realistic touch leaving a permanent wake-up call effect on the reader to change their anthropocentric way of living through a posthuman perspective.

Tracking heatwave extremes from an event perspective

Public perceptions of the risk posed by natural hazards and climate change are typically associated with extreme events. While there are studies focused on the detailed synergy for processes that lead to the event occurrence. Past literature working on long-term variations of global weather and climate extremes often studies the derived indices and applies further statistical models to data sampled from a fixed grid point or area. Our study, using extreme heatwave events as an example, proposes an alternative framework to track and analyze extremes from an event perspective to facilitate better climate risk communication.With a selected threshold of daily heatwave intensity and an objective spatial and temporal connectivity algorithm, we introduce an event-tracking method to automatically track all global heatwaves based on long-term reanalysis data. Two nearby but separate European heatwave events (Scandinavia and France) in 2003 are used to demonstrate the validity of our event-tracking method. We further highlight the genesis frequency, occurrence density, and tracks of all historical heatwave events over global land areas from 1979 to 2018. The contributions from heatwave intensity, the affected area, and temporal evolution to each extreme event are documented. With the retaining spatial and temporal evolutions of tracked heatwave events during their lifespans, the precursory and concurrent environmental conditions associated with the event can be further studied. The integrated size and scale measures of extreme heatwave events can be compared historically in a region and/or across different climate regimes. They also provide better information for the risk assessment on event-associated loss and damages, and can easily be extended to study compound hazards with intersections of different types of extreme events.

Moisture recycling and the potential role of forests as moisture source during European heatwaves

Heatwaves are extreme weather events that have become more frequent and intense in Europe over the past decades. Heatwaves are often coupled to droughts. The combination of them lead to severe ecological and socio-economic impacts. Heatwaves can self-amplify through internal climatic feedback that reduces local precipitation. Understanding the terrestrial sources of local precipitation during heatwaves might help identify mitigation strategies on land management and change that alleviate impacts. Moisture recycling of local water sources through evaporation allows a region to maintain precipitation in the same region or, by being transported by winds, in adjacent regions. To understand the role of terrestrial moisture sources for sustaining precipitation during heatwaves, we backtrack and analyse the precipitation sources of Northern, Western, and Southern sub-regions across Europe during 20 heatwave periods between 1979 and 2018 using the moisture tracking model Water Accounting Model-2layers (WAM-2layers). In Northern and Western Europe, we find that stabilizing anticyclonic patterns reduce the climatological westerly supply of moisture, mainly from the North Atlantic Ocean, and enhances the moisture flow from the eastern Euro-Asian continent and from within their own regions—suggesting over 10% shift of moisture supply from oceanic to terrestrial sources. In Southern Europe, limited local moisture sources result in a dramatic decrease in the local moisture recycling rate. Forests uniformly supply additional moisture to all regions during heatwaves and thus contribute to buffer local impacts. This study suggests that terrestrial moisture sources, especially forests, may potentially be important to mitigate moisture scarcity during heatwaves in Europe.