Spatially Compounding Drought-Flood Events Are Favored by Atmospheric Blocking Over Europe

Droughts and floods can occur simultaneously at the continental scale, resulting in impacts from both excess and deficit of water at the same time. Such spatially compounding drought-flood events can result in contrasting water management challenges. Despite their relevance for insurance and management, we know little about their occurrence, seasonality, and large-scale atmospheric drivers. We address this research gap by studying spatially compounding drought-flood events using streamflow and precipitation observations in Europe. Our results show that these compounding events have a strong seasonality and occur most often during winter, spring, and in June, even though their meteorological counterpart, spatially compounding dry-wet extremes, mainly occur in summer. Each of these events has its own spatial footprint. These footprints can be categorized in four main clusters, with the flood part of the compounding extreme either occurring over Central Europe or the UK in summer or winter, Eastern Europe in spring, or Southern Europe in winter. Our analysis of the relationship between seven European weather regimes and spatially compounding drought-flood events shows that these events are mainly favored by different types of blocking regimes in winter, spring, and summer and by the Zonal Regime in winter and spring. These weather regimes are all related to stable high-pressure systems located over one part of Europe and cyclonic conditions at their edges over another part of Europe. We conclude that spatially compounding drought-flood events are favored by particular weather regimes, whose relative importance depends on the season and the location of the flood hotspot.