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 socio-economic sector. 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 the prolonged heat has become more likely due to 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.

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).…”

Weather persistence on sub-seasonal to seasonal timescales: a methodological review

“…Separating distinct occurrences of a state, pattern or event is critical to distinguish recurrence from stationarity. Over short periods, like a season, it is in principle possible to visually separate multiple systems occurring in close succession, for instance with Hovmoeller diagrams (e.g., Rousi et al, 2022a). Most of the time, however, separation cannot be done by hand, and objective criteria are required.…”

“…The first option is to choose a single, fixed timescale for analysis. This choice can be guided by impact and forecasting considerations, by physical knowledge of the underlying system, or by observations of persistent events (e.g., Huntingford et al, 2014;Lawrence et al, 2020;Overland and Wang, 2021;Rakovec et al, 2022;Rousi et al, 2022a). This is the most common approach to analyse episodic persistence, but it is also applicable to global persistence.…”

Implementation of a Satellite-Based Tool for the Quantification of CH4 emissions over Europe (AUMIA v1.0) – Part 1: Forward Modeling Evaluation against Near-Surface and Satellite Data

“…According to Kaplan (2002), potential natural wetlands in the 30 km modeling domain concentrate over the Baltic countries, Belarus and western regions of Russia. Among the factors that could have negatively influenced the accumulation of biospheric CH4 in the atmosphere over the study region are: a less CH4 formation tied to the extremely dry season in summer 2018 over central and northern Europe (Rousi et al, 2022); a CH4 compensation by soil uptake processes; and Concentrations were averaged for grid points with satellite measurements during the period from May 1 to August 31, 2018, months with the best model performance for smoothed concentrations (see Fig. 4).…”