| 10 Aug 2026
Large droughts are not large small droughts: hydro-meteorological drought generation processes vary with streamflow drought size in the Alpine region
Abstract. Streamflow droughts can be caused by a range of processes which can show strong heterogeneity from basin to basin. In contrast to local droughts, spatially extensive droughts seem to have more spatially homogeneous driving processes. However, the underlying mechanisms that cause this difference in the generation processes of small vs. large droughts are not well understood. This study presents an observation-based analysis that bridges this scale gap between large and small streamflow droughts. We assess how drought generation processes vary with drought size by classifying droughts into different types using streamflow drought observations and different hydro-meteorological variables. We find that: (1) most large drought events are characterized by one or two drought types even in hydro-climatically complex regions such as the Alps; (2) each drought type has its own spatial footprint and only specific drought types can lead to large droughts; and (3) in recent years, large droughts have increasingly been characterized by a mix of drought types. Our results highlight that the most common drought type in a catchment might not always lead to large droughts, which can be important for water management.
Competing interests: Manuela Brunner is an editor with HESS. The authors declare no further competing interests.
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