Spatiotemporal Dynamics of Streamflow Drought in the Larger Alpine Region

Streamflow droughts are spatial phenomena that are generally not restricted to individual rivers or catchments. However, many studies spatially limit their drought analysis, for example focusing on a specific country or catchment only, which makes it difficult to study spatiotemporal drought evolution in detail. Here, we analyze the spatiotemporal dynamics of streamflow droughts over the larger Alpine region using spatially-explicit and high-resolution simulations from the hydrological model PCR-GLOBWB2.0. Specifically, we apply a novel spatial and temporal clustering algorithm to track streamflow drought events in space and time. Our results show that spatially-extensive streamflow droughts ((Formula presented.) 500km of river network) typically experience phases of growth and recovery, during which extensive drought events sometimes consist of several spatially-distinct sub-events. Streamflow droughts behave differently in different geographic regions. Drought extent is often limited by the Alpine mountain range and the mountain river network is less frequently part of spatially-extensive drought events than the surrounding lowland rivers. Furthermore, the spatial evolution of streamflow drought is affected by different hydrometeorological drivers. Rainfall deficits are the most dominant driver of spatially-extensive streamflow drought in the study domain, but many drought events result from the interplay of multiple processes. The dominant drivers of streamflow droughts change over time as the affected domain changes. Since drought extent can influence the effectiveness of drought impact mitigation strategies, a better understanding of the spatiotemporal dynamics of streamflow drought has important implications for future water management.