A comparative analysis of hydrological drought in the Rur catchment under human and natural impacts

Rur river catchment, North Rhine-Westphalia (NRW), Germany In a changing climate, the propagation of drought through coupled groundwater–surface water systems remains difficult to investigate, particularly in catchments strongly influenced by human activities. This study presents a joint analysis of groundwater and streamflow droughts in the anthropogenically influenced Rur river catchment. Standardized indices were computed for 209 groundwater wells (standardized groundwater level index, SGI) and 16 streamflow gauges (standardized streamflow index, SSI). Hierarchical clustering yielded five groundwater clusters (SGI_C1–SGI_C5) and three streamflow clusters (SSI_C1–SSI_C3). Cluster-mean hydrographs were analyzed using run theory and cross-correlation to characterize regional drought attributes and the propagation process. Regional groundwater droughts are strongly modulated by anthropogenic activities and local hydrogeology. Notably, SGI_C2 shows a persistent declining trend, associated with nearby lignite open-pit mining. SGI_C5, comprising wells near the Rur, exhibits shorter mean drought durations. In contrast, streamflow droughts respond rapidly to precipitation deficits and vary with topographic setting. The mountainous cluster SSI_C2 shows the strongest correlation with the standardized precipitation index (SPI; r = 0.60). In lowland regions, strong groundwater–surface water coupling is evident, with moderate-to-strong correlations between SGI_C5 and SSI_C1 (r = 0.55) and between SGI_C1 and SSI_C3 (r = 0.45), implying that concurrent groundwater drought can intensify streamflow drought. Reservoir operations mitigate streamflow drought severity in SSI_C1 relative to SSI_C3, which more closely reflects natural flow and exhibits more pronounced droughts. The study provides a transferable workflow for investigating hydrological drought propagation under anthropogenic influence. It highlights the roles of human water management, precipitation variability, and groundwater–river interaction in shaping drought dynamics across the groundwater and stream flow system. • Integrated drought analysis used clustering, run theory, and cross-correlation. • Five groundwater (SGI C1–C5) and three streamflow clusters (SSI C1–C3) were identified. • Groundwater–streamflow interactions strongly shape drought characteristics and propagation.