Pathways of drought propagation in near-natural catchments across Germany

Drought is one of the costliest natural hazards of widespread occurrence and long-lasting economic, social, and environmental consequences. Droughts are gradual phenomenon with far-reaching effects that develop over time. Therefore, understanding how drought conditions spread through the terrestrial compartments is essential for predicting impacts, adjusting mitigation strategies, and enhancing climate adaptation. Here, we analyze and characterized drought propagation from meteorological to streamflow and groundwater observations in more than 500 selected river catchments (areas below 300 km²⁾, hosting 13,500 shallow and deep groundwater wells in Germany using the variable threshold level method. We use daily meteorological and streamflow data from CAMELS-DE (Loritz et al.,2024) and a biweekly dataset of groundwater observation compiled from German water authorities, covering the period 1980 to 2020. Among near-natural German river catchments (with no noticeable direct human influence on river flow through reservoir storage and or abstractions), we find four main drought propagation archetypes that evidence the strong coupling or decoupling of surface and subsurface waters: (1) catchments with very reactive groundwater but unresponsive streamflow, where groundwater droughts onset almost immediately in response to meteorological droughts, while the response of streamflow is delayed; (2) fast reactive catchments with delayed response of groundwater droughts; (3) slow reactive catchments characterized by the delayed propagation of groundwater droughts and long recovery times; and (4) very resilient catchments where only the most severe meteorological droughts manifest in either streamflow or groundwater droughts. Our results provide insights on the spatial variability of drought propagation mechanisms at a national scale that can be used to pinpoint the hotspots of rapid drought onset and slow recovery that require targeted mitigation and adaptation strategies.

Loritz, R., Dolich, A., Acuña Espinoza, E., Ebeling, P., Guse, B., Götte, J., Hassler, S. K., Hauffe, C., Heidbüchel, I., Kiesel, J., Mälicke, M., Müller-Thomy, H., Stölzle, M., and Tarasova, L.: CAMELS-DE: hydro-meteorological time series and attributes for 1582 catchments in Germany, Earth Syst. Sci. Data (2024) Vol. 16 Issue 12. DOI: 10.5194/essd-16-5625-2024