Hydrological drought classification in Europe

We propose a formal classification scheme for streamflow droughts in humid-temperature climate regions. The classification scheme relies on an existing drought typology and assigns events to one of eight drought types - each characterized by a set of compounding drivers - using information about seasonality, precipitation deficits and snow availability.
To ensure generalizability, the classification scheme uses globally available data i.e. observed streamflow from the Global Runoff Database and hydro-meteorological time series from the ERA5-Land reanalysis including temperature, precipitation, and snow-water-equivalent (SWE).
Hydrological drought types include rainfall deficit droughts, which are exclusively caused by a prolonged lack of rainfall and possibly aggravated by high evapotranspiration; rain-to-snow-season droughts, caused by a rainfall deficit in the rain season continuing into the snow season; wet-to-dry season droughts caused by a rainfall deficit in the rain season that continues into the dry season; cold-snow-season droughts, caused by abnormally low temperatures in the snow season; warm-snow-season droughts, caused by abnormally high temperatures in the snow season; snowmelt droughts, caused by a lack of snowmelt discharge in snow-influenced basins; glaciermelt droughts, caused by a lack of glaciermelt; and composite droughts, caused by a number of drought generation mechanisms.