Compound events in Germany in 2018: drivers and case studies

Europe frequently experiences 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, known as compound events. We investigate the interactions between extreme weather events, their characteristics, and changes in their intensity and frequency, as well as uncertainties in the past, present, and future. We also explore their impacts on various socio-economic sectors in Germany and central Europe. This contribution highlights several case studies with special focus on 2018, a year marked by an exceptional sequence of compound events across large parts of Europe, resulting in severe impacts on human lives, ecosystems, and infrastructure. We provide new insights into the drivers of spatially and temporally compound events, such as heat and drought, and heavy precipitation combined with extreme winds, and their adverse effects on ecosystems and society, using large-scale atmospheric patterns. We also examine the interannual influence of droughts on surface water and the impact of water scarcity and heatwaves on agriculture and forests. We assess projected changes in compound events at different current and future global surface temperature levels, demonstrating the need for improved quantification of future extreme events to support adaptation planning. Finally, we address research gaps and future directions, stressing the importance of defining composite events primarily in terms of their impacts prior to their statistical characterisation.