Streamflow drought intensification in the European Alps
A five-decade analysis of drought generation processes in the Alps shows their changing seasonality in high-elevation basins with increasingly frequent droughts caused by a lack of snowmelt water.
The European Alps, sometimes described as the ‘water towers of Europe’, represent an important source of freshwater for millions of people residing in their watersheds. Understanding hydrology and particularly the streamflow drought regime of the Alps is critical for water management and growing hydropower production in the region.
Brunner et al.  analyze the seasonality and relative frequency of different drought types in the region. Drought types have substantially changed over the past 50 years. Changes are more pronounced in high-elevation (greater than 1,500 meters) watersheds that exhibit more frequent occurrence of snowmelt-deficit droughts (caused by a lack of snowmelt discharge in spring and summer), with rainfall-deficit droughts (due to low rainfall and high evapotranspiration) and cold-snow-season droughts (caused by abnormally low temperatures in the snow season) becoming relatively less important. Such changes in the dominant type of drought generation mechanism have also increased drought severity in these watersheds, raising questions as to whether these trends will persist into the future.