ALBERT

Description: 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.

Description: The frequency of occurrence of extreme weather events, such as heat waves, severe storms, and extreme precipitation has increased dramatically in recent years and is expected to further increase with rising global temperatures. Extreme weather events and their changing characteristic due to rising global temperatures have a large societal impact. Exemplary, extremely warm summers can lead to severe health problems and are thus associated with an increased mortality. Furthermore, economic impacts, such as crop failure and water shortage, and political aspects, such as climate migration and general crisis management are associated with extremely warm summers. Reliable and precise predictability years in advance of these high-impact events would be crucial to reduce potential impacts. We use the demonstrated processes connecting the North Atlantic circulation and European temperatures (Hellmich et al., in review) to enhance the prediction skill of extremely warm European summers. The North Atlantic heat inertia can drive extremely warm European summers on sub-decadal time scales, thus acting as a precursor for the occurrence of such extreme events. Here we demonstrate how the sub-decadal North Atlantic heat inertia can be used to predict extremely warm European summers several years in advance, using a decadal hindcast ensemble based on the Max-Planck-Institute Earth system model.