2018 European heatwave
The 2018 European heatwave consisted of multiple episodes of extreme high temperatures across northern, central, and western Europe during late spring through early autumn, culminating in the warmest summer on record for many regions since instrumental measurements began.[1] Driven primarily by a persistent blocking high-pressure system over Scandinavia that inhibited typical westerly flows and precipitation, the event produced temperature anomalies exceeding 5°C above seasonal norms in parts of northern Europe, shattering national records in countries including Finland, Sweden, and the United Kingdom.[2] [3] The heatwave's intensity and duration—featuring extended periods of days with maximum temperatures over 25°C across large areas—exceeded thresholds observed in prior decades, contributing to severe soil moisture deficits and widespread drought conditions.[4] [1] These meteorological extremes amplified ecological stresses, including accelerated lake surface warming, reduced river discharges, and nutrient limitations in coastal systems, while igniting numerous wildfires and causing substantial agricultural yield reductions.[5] [6] The heat also imposed direct physiological burdens on human populations, particularly the vulnerable elderly, leading to elevated rates of heat-related illnesses and excess mortality, though precise continental totals remain subject to methodological variations in attribution studies.[7] Economically, the event disrupted energy demands, transportation, and water resources, underscoring vulnerabilities in infrastructure adapted to milder historical climates.[1] Despite its severity, analyses indicate the heatwave's occurrence aligned with natural atmospheric variability patterns, such as positive East Atlantic circulation indices, though superimposed on a backdrop of gradual atmospheric warming.[4]Overview
Event Summary
The 2018 European heatwave consisted of multiple prolonged episodes of extreme heat affecting large portions of the continent, particularly northern and central Europe, from late spring through early autumn. Characterized by unusually stable anticyclonic conditions, the event led to the second-warmest summer on record for Europe following 2010, with significant temperature anomalies driven by persistent high-pressure systems.[1][8] These conditions began emerging in April, with extended warm periods through May and June in western regions, escalating to peak intensities in July across Scandinavia and central Europe, before shifting southward in August.[9][4] Record-breaking temperatures were observed in multiple locations unaccustomed to such extremes, including new national highs in Sweden and Finland, with anomalies exceeding 5-10°C above seasonal norms in the Baltic region.[2] In June alone, western Europe experienced its warmest on record, with two distinct heatwaves peaking around mid-month and early July, pushing feels-like temperatures over 38°C in southern areas.[10] The prolonged dry conditions exacerbated drought, impacting agriculture, water resources, and ecosystems across the affected regions.[1] The heatwave's severity was compounded by low soil moisture from preceding deficits, amplifying surface heating through reduced evaporative cooling, and contributed to widespread wildfires, crop failures, and public health strains, including excess mortality particularly among vulnerable populations.[1] While comprehensive continent-wide mortality figures remain subject to varying attribution methods, the event underscored vulnerabilities in temperate climates to sustained high temperatures.[4]Geographical Scope and Severity
The 2018 European heatwave encompassed a broad geographical area spanning northern, central, and western Europe, with notable extensions into southern regions such as Iberia during August. The event originated with intense heat in Scandinavia starting in mid-July, subsequently propagating southward to central Europe in late July, while southern areas experienced peaks later in the season.[1] Affected nations included Norway, Sweden, Finland, Denmark, the United Kingdom, Germany, France, the Netherlands, Belgium, and Switzerland, among others, where prolonged high temperatures combined with drought conditions amplified impacts.[2] [4] Severity was most pronounced in northern Europe, where persistent high-pressure systems generated temperature anomalies exceeding 5°C above seasonal norms in northern Scandinavia and western Ireland. In Norway, the Arctic Circle community of Bardufoss recorded 33.5°C on July 17, marking an exceptional northward reach of extreme heat. Finland observed maxima up to 33.4°C, while Sweden and Denmark faced unprecedented summer warmth leading to widespread wildfires and agricultural stress. Central Europe endured extended hot spells from early spring through autumn, with anomalies peaking in regions like Germany and Poland, where the number of days exceeding 25°C set new records.[2] [11] [12] Western Europe registered its warmest June on record, with regional averages culminating at 24.9°C on June 30 across France, the United Kingdom, Spain, and Portugal. The United Kingdom experienced a peak of 35.3°C in Faversham on July 26, contributing to the joint hottest summer nationally. Multiple stations in Scandinavia and central Europe shattered all-time maxima, highlighting the event's rarity relative to historical baselines. Accompanying deficits in precipitation exacerbated drought across 22% of Europe's agricultural lands, intensifying the heat's ecological and societal toll.[10] [13] [4]Meteorological Drivers
Atmospheric Patterns and Blocking Highs
The 2018 European heatwave was primarily driven by a persistent atmospheric blocking pattern characterized by a high-pressure ridge over northern Europe, particularly centered over Scandinavia and the Baltic region, which stalled the typical westerly zonal flow of mid-latitude weather systems.[1] This blocking high, evident from late June onward, featured strongly positive geopotential height anomalies at 500 hPa levels over Scandinavia, preventing the eastward progression of Rossby waves and low-pressure systems from the North Atlantic.[7] [14] The ridge formed through the amplification of a Rossby wave train, transitioning into a quasi-stationary configuration that trapped hot continental air masses and allowed for radiative warming under prolonged clear skies.[1] This blocking regime promoted subsidence within the high-pressure core, enhancing adiabatic warming and suppressing precipitation, which contributed to the heatwave's intensity across central and northern Europe from mid-June to August.[15] [16] The pattern was reinforced by a positive phase of the summer North Atlantic Oscillation (NAO), which steered warm southerly flows from subtropical regions northward, bypassing usual cyclonic activity.[1] Analyses indicate that the blocking persisted for weeks, with the high-pressure anomaly over Scandinavia active from May through July, leading to anomalously high temperatures and drought conditions in affected areas.[2] Comparisons with prior events highlight the 2018 blocking as unusually stable and prolonged, akin to but exceeding the duration seen in the 2003 heatwave, due to the ridge's meridional elongation and resistance to breakdown from upstream wave propagation.[7] [14] Meteorological models from the European Centre for Medium-Range Weather Forecasts (ECMWF) captured this pattern's evolution, showing elevated predictability in extended-range forecasts owing to the blocking's quasi-resonant Rossby wave structure.[16] The absence of significant tropospheric instability further sustained the high, as minimal convective activity failed to erode the ridge, perpetuating the heat dome effect over much of the continent.[1]Preceding Conditions and Seasonal Anomalies
Europe experienced a transition from cold early spring conditions to warm and dry weather starting in April 2018, setting the stage for the summer heatwave. February and March featured below-average temperatures and exceptional snowfall across much of the continent, but from April onward, warmer and drier patterns emerged, with persistent high-pressure systems contributing to reduced precipitation.[17][1] Spring 2018 (March-May) was exceptionally warm and dry in central and northern Europe, with late spring temperatures exceeding 2.5°C above the 1981-2010 average in central regions. Precipitation totals fell below 80% of normal levels in these areas, leading to soil moisture deficits that persisted into summer.[17][18][19] These anomalies amplified the heatwave's intensity, as low soil moisture reduced latent heat flux and evapotranspiration, increasing sensible heating and surface temperatures during subsequent hot periods. A persistent high-pressure anomaly over Scandinavia from May onward further suppressed rainfall, exacerbating drought conditions.[20][2][1]Chronology
June Phase
The June phase of the 2018 European heatwave featured two primary heat events driven by persistent high-pressure systems, resulting in the warmest June on record for western Europe. The first event peaked from 17 to 22 June, affecting large areas of western and southern Europe through a 'heat dome' configuration that trapped warm air masses and suppressed precipitation.[10] [10] These conditions produced prolonged periods of hot, sunny, and dry weather, with temperatures significantly above seasonal norms across the region.[10] A second heatwave emerged at the month's end, bridging into early July and further entrenching the blocking pattern over northern and western Europe.[10] In the United Kingdom, this phase coincided with exceptionally dry conditions, especially in central and southern England, where some locations near London recorded little to no rainfall over extended periods approaching 57 days.[21] A dominant high-pressure ridge over the British Isles and North Sea reinforced the stagnation of weather systems, limiting convective activity and exacerbating aridity.[19] These early anomalies depleted soil moisture levels, creating feedback mechanisms that intensified surface heating by reducing evaporative cooling.[22] While not yet reaching the peak intensities of later months, the June events laid the groundwork for widespread drought, with northern Europe experiencing elevated temperatures under a quasi-stationary high-pressure influence extending from May.[2] Impacts during this phase were primarily preparatory, including initial strain on water resources and agriculture, though human health effects remained limited compared to subsequent periods.[16]July Peak
The July phase marked the peak intensity of the 2018 European heatwave, with northern Europe experiencing unprecedented heat under a persistent high-pressure system. Temperatures across Scandinavia were substantially elevated, contributing to the European monthly average anomaly of +1.7°C above the 1981-2010 baseline, the second highest July on record.[23] Independent analysis from NOAA indicated a +2.33°C departure from average, also ranking as the second warmest July since continental records began in 1910.[24] Mid-July saw the heatwave's northern apex, as anomalies intensified over Norway, Sweden, and Finland, with maximum temperatures surpassing 30°C as far north as the Arctic Circle. On July 17, Bardufoss in northern Norway registered 33.5°C, establishing a provisional national record for the location.[11] This event reflected the southward progression of prior warmth, exacerbated by blocked atmospheric patterns that trapped heat and suppressed precipitation.[2] By late July, the high-pressure ridge shifted toward central Europe, extending extremes to regions like Germany, the Benelux countries, and the United Kingdom, where monthly averages also deviated positively from norms.[23] In Finland, southern stations recorded peaks including 33.7°C in Porvoo and 33.2°C in Helsinki on July 28, underscoring the month's record-breaking maxima in multiple locales.[25] Overall, July shattered daily and monthly temperature records in several northern and central sites, amplifying drought conditions initiated earlier in the season.[1]August Extension and Aftermath
The 2018 European heatwave extended into August, with the month recording the highest average temperatures across the continent since records began, exceeding previous benchmarks by a significant margin.[16] This prolongation followed persistent high-pressure blocking patterns that had dominated since June, sustaining elevated temperatures and minimal precipitation over large areas.[4] In northwestern Europe, heat episodes continued from mid-July into early August, while a particularly intense short-duration event struck the western Mediterranean region at the month's start, pushing local maxima above 40°C in parts of Spain and Portugal.[7][4] August's extreme conditions exacerbated ongoing drought, leading to reduced river discharges and diminished nutrient inputs to coastal waters, which in turn caused rapid surface water warming and altered marine ecosystems.[6] Wildfire activity, fueled by the cumulative dryness, persisted in northern regions like Scandinavia, where the heatwave's extension intensified fire risks amid parched forests.[26] Human health burdens mounted as well, with the sustained thermal stress correlating to elevated incidences of heat-sensitive infections, such as Shiga toxin-producing E. coli enteritis and campylobacteriosis in areas like Ireland.[27] In the aftermath, forest ecosystems showed signs of strain without immediate widespread tree mortality; for instance, many species experienced stem dehydration and temporary shrinkage from depleted water reserves, but annual growth rates were not uniformly suppressed.[28] However, physiological recovery in trees was notably impaired, rendering stands more susceptible to secondary stressors like pests or subsequent droughts in the years following 2018.[29] Broader ecological damage from the 2018 event, compounded by recurring heat and drought through 2022, contributed to documented losses in European forest health, highlighting vulnerabilities amplified by the August extension's severity.[30]Human Health Impacts
Mortality Statistics
The 2018 European heatwave led to significant excess mortality, particularly among the elderly and those with pre-existing health conditions, though precise attribution to heat remains methodologically challenging due to confounding factors like underlying diseases and varying national reporting standards. Peer-reviewed analyses and official health agency estimates indicate thousands of additional deaths across affected countries, with higher burdens in central and northern Europe where temperatures were most anomalous.[31][32]| Country | Estimated Excess/Heat-Related Deaths | Notes/Details |
|---|---|---|
| Germany | 8,700 | Based on national mortality data analysis attributing deaths to elevated temperatures during the summer period; primarily affected older populations.[31] |
| France | ~1,500 | Official figures from health authorities linking deaths to prolonged high temperatures over the summer; concentrated in urban areas and among seniors.[33] |
| United Kingdom | 650–700 | Excess over seasonal averages during peak heat episodes in June–July and late July; vulnerable groups included those over 75 years.[34] |
| Sweden | 750 | Excess during early July to early August, as estimated by the Public Health Agency; heat attribution models confirmed direct temperature-mortality links.[32] |