Snow drought propagation and its impacts on streamflow drought in the Alps

Abstract Snow droughts, that is negative anomalies in annual snow storage, challenge water resources management in snow-rich catchments and their downstream regions because they can lead to succeeding streamflow droughts in the following melt season. Under continued global warming, snow droughts are expected to become more frequent and intense, which likely increases the occurrence of succeeding streamflow droughts. However, we still know little about the rate at which snow droughts propagate to subsequent streamflow droughts, the spatial patterns of these concurrent events, the influence of snow drought characteristics on the occurrence, deficit, and duration of streamflow droughts, and temporal changes in snow drought propagation. To address these research gaps, we developed a novel dynamic bi-directional snow-to-streamflow drought propagation scheme, that resulted in a unique dataset of concurrent snow and streamflow droughts for 207 catchments in Switzerland and Austria. We found that in the period from 1961 to 2020, 18% of the snow droughts propagated to a streamflow drought, and that 21% of the spring/summer streamflow droughts were preceded by a snow drought. Snow-to-streamflow droughts are most common in catchments at high elevations without glaciers and among the snow droughts with the largest deficits and longest durations. In general, snow droughts lead to streamflow droughts with higher deficits, longer durations, and earlier occurrences. In the last six decades, the number of snow droughts has increased, which resulted in a doubling of snow-to-streamflow drought events in 1991–2020 compared to 1961–1990. As snow droughts are expected to further increase due to climate change, the propagation of snow-to-streamflow droughts will likely increase in medium to high elevation catchments and lead to more frequent and intense spring and summer droughts in the Alps.