Compound events in Germany in 2018: drivers and case studies

Abstract. The European continent is regularly affected by a wide range of extreme events and natural hazards including heatwaves, extreme precipitation, droughts, cold spells, windstorms, and storm surges. Many of these events do not occur as single extreme events, but rather show a multivariate character, the so-called compound events. Within the scope of the interdisciplinary project climXtreme (https://climxtreme.net/), we investigate the interplay of extreme weather events, their characteristics and changes, intensity, frequency and uncertainties in the past, present and future and associated impacts on various socio-economic sectors in Germany and Central Europe. This contribution presents several case studies with special emphasis on the calendar year of 2018, which is of particular interest given the exceptional sequence of different compound events across large parts of Europe, with devastating impacts on human lives, ecosystems and infrastructure. We provide new evidence on drivers of spatially and temporally compound events (heat and drought; heavy precipitation in combination with extreme winds) with adverse impacts on ecosystems and society using large-scale atmospheric patterns. We shed light on the interannual influence of droughts on surface water and the impact of water scarcity and heatwaves on agriculture and forests. We assessed projected changes in compound events at different current and future global surface temperature levels, demonstrating the importance of better quantifying the likelihood of future extreme events for adaptation planning. Finally, we addressed research needs and future pathways, emphasising the need to define composite events primarily in terms of their impacts prior to their statistical characterisation.