The extremely hot and dry 2018 summer in central and northern Europe from a multi-faceted weather and climate perspective

Abstract

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 the 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 in mid-July and 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 already identified in spring. While in the early stages over Scandinavia the air masses at mid and upper levels were often of a remote, maritime origin, at later stages over Iberia the air masses primarily had 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 that of 2018 is expected to occur every 2 out of 3 years in Europe in a +1.5 ∘C warmer world and virtually every single year in a +2 ∘C warmer world. 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 their effects and provide valuable information as a basis for adaptation and mitigation strategies.

Long‐term variability and trends of meteorological droughts in Ukraine

“…As the droughts are facilitated by the high frequency of anticyclonic circulation and blocking processes in the troposphere, the drought propagation gradient within a certain area will obviously be linked to the relative position of the blocking centre (Cherenkova et al, 2015; Kautz et al, 2022). However, studies show that this fact on its own does not fully explain the intensity and duration of the drought (Fink et al, 2004; Rousi et al, 2023). In addition, accompanying peripheral processes cause dry winds in different parts of Ukraine, locally called “sukhovei” (Semenova & Slizhe, 2020), which can intensify and accelerate drought manifestation and lead to flash drought (Otkin et al, 2013).…”

Record-breaking and unprecedented compound hot and dry summers in Europe under different emission scenarios

“…However, it must be noted that the full range of possible future events can be much larger (as shown for instance in figure 6 where all model results are shown); as a consequence, our findings may underestimate the risk of high-impact low-likelihood events, even under the low-emission scenario. • (5) Finally, our study does not investigate the physical mechanisms (or the change in the mechanisms) leading to (past and future) heat waves, droughts and, ultimately, CHD events (Ionita et al 2021, Herrera-Lormendez et al 2023, Rousi et al 2023. As mentioned, these mechanisms are very complex and include both dynamic and thermodynamic factors, at both large (circulation patterns) and local (e.g.…”

“…Under future warmer conditions, the dependence between temperature and precipitation can strengthen further, with higher evaporation causing soils to dry earlier and, ultimately, increasing the probability of CHD events (Zscheischler and Seneviratne 2017), even of those that are today considered extreme, such as the 2018-2019 CHD event in Germany (Toreti et al 2019, Zscheischler and Fischer 2020, Rousi et al 2023.…”

Impact of drought hazards on flow regimes in anthropogenically impacted streams: an isotopic perspective on climate stress

“…Contemporary tracer-based catchment inter-comparisons using high resolution isotope data are still rare in the context of urbanization and agricultural intensification (Bonneau et al, 2018;Marx et al, 2023). Despite a wet year in 2017, 2018 had a dry late winter with low regional groundwater levels, which progressively declined during a hot, dry summer, turning into an extreme 200 year drought with significant impacts for agriculture, ecology and river flows (Beillouin et al, 2020;Rousi et al, 2023). Under the most climate change scenarios, further declines in groundwater levels by the end of the century are expected for North and Eastern Germany with dry-hot seasons getting longer, exacerbating existing patterns of increased streamflow intermittency and low flows (Tramblay et al, 2021;Wunsch et al, 2022).…”