Hydrological Drought Generation Processes and Severity Are Changing in the Alps

Streamflow droughts are governed by different hydro‐meteorological processes, whose relative importance may change over time, with potential impacts on drought severity. Here, we assess changes in the importance of different hydrological drought generation processes in the European Alps by applying a standardized drought type classification scheme to two time periods—one in the distant (1970–1993) and one in the recent past (1994–2017). Our findings show that changes in the relative importance of different drought generation processes are stronger in high‐elevation catchments, where we detect clear changes in drought seasonality, than in low‐elevation catchments. Furthermore, they suggest that changes in drought severity and generation processes are related because increasingly frequent snowmelt‐deficit droughts in high‐elevation catchments have larger deficits than droughts caused by decreasingly frequent cold temperatures. These changes might persist into the future, because of continuing decreases in snow cover and increases in evapotranspiration, with potential implications for water management. Plain Language Summary Droughts are caused by a range of different processes including rainfall and snowmelt deficits or high evaporation. Depending on their generation processes, droughts have different severities. Because of this relationship between drought generation processes and those severities, drought severities might change as a result of changes in drought generation processes. In this study, we assess how the relative importance of rainfall deficits, snow‐melt deficits and other drought generation processes has changed over time in the European Alps, specifically the Rhine, Rhone, and Danube river basins. For this change assessment, we looked at different drought types over the period from 1970 to 2017. We find that changes in the relative importance of different drought generation processes are stronger in high‐elevation regions influenced by snow because of clear changes in drought seasonality than in low‐elevation regions mainly influenced by rainfall. Our results also suggest that these changes in drought generation processes have led to changes in drought severity. These changes might persist into the future, because of continuing decreases in snow cover and increases in evaporation, with potential implications for water management. Key Points We assess past changes in the relative frequency of different hydrological drought types in the Alps u