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Abstract:
The summer of 2018 was an extraordinary season in climatological terms for northern and
central Europe, bringing simultaneous, widespread, and concurrent heat and drought extremes in large
parts of the continent with extensive impacts on agriculture, forests, water supply, and socio-economic
sector. Here, we present a comprehensive, multi-faceted analysis of the 2018 extreme summer in terms
of heat and drought in central and northern Europe, with a particular focus on Germany. The heatwave
first affected Scandinavia by mid-July, shifted towards central Europe in late July, while Iberia was
primarily affected in early August. The atmospheric circulation was characterized by strongly positive
blocking anomalies over Europe, in combination with a positive summer North Atlantic Oscillation and
a double jet stream configuration before the initiation of the heatwave. In terms of possible precursors
common to previous European heatwaves, the Eurasian double jet structure and a tripolar sea-surface
temperature anomaly over the North Atlantic were identified already in spring. While in the early stages
over Scandinavia the air masses at mid- and upper-levels were often of remote, maritime origin, at later
stages over Iberia the air masses had primarily a local-to-regional origin. The drought affected Germany
the most, starting with warmer than average conditions in spring, associated with enhanced latent heat
release that initiated a severe depletion of soil moisture. During summer, a continued precipitation
deficit exacerbated the problem, leading to hydrological and agricultural drought. A probabilistic
attribution assessment of the heatwave in Germany showed that such events of prolonged heat have
become more likely due to anthropogenic global warming. Regarding future projections, an extreme
summer such as this of 2018 is expected to occur every two out of three years in Europe under a 1.5 °C
warmer world and virtually every single year under 2 °C of global warming. With such large-scale and
impactful extreme events becoming more frequent and intense under anthropogenic climate change,
comprehensive and multi-faceted studies like the one presented here quantify the multitude of effects
and provide valuable information as basis for adaptation and mitigation strategies.
