Isotope tracers reveal summer drought effects on urban water systems and their recovery in Berlin, Germany

Abstract:

With proceeding urbanization around the globe, precise knowledge of water cycling in large urban areas is crucial to secure a sustainable water supply in the future. Especially the potential of increasing climate warming and changing precipitation patterns poses risks on urban water systems. Following the exceptionally warm and dry summer of 2018, we performed spatially-distributed, seasonal, synoptic sampling of surface- and groundwater across the large metropolitan area of Berlin, Germany, to trace water cycling in an urban system recovering from drought conditions using stable isotopes. Our results indicate that especially the Spree and Havel rivers, characterized by large catchments outside the city boundaries, and wetland-impacted local streams experienced substantial evaporative losses, whose impacts could be traced well into the autumn and winter months. Smaller urban, groundwater-fed streams showed better resilience to such evaporative losses, but more pronounced short-term variability as they received runoff from stormwater drainage and impervious surfaces during larger precipitation events. Effluent-impacted streams were least affected by seasonal fluctuations. Combined with proceeding investigations of ecohydrological partitioning under the complex mosaic of urban green spaces and a more efficient source identification between effluents and groundwater in closed urban water cycles, our approach, which combines isotopic, hydrogeochemical, climatic and hydrometric data, provides profound insights into urban water cycling in a changing environment and an evidence base for adapting water management strategies in urban areas to future challenges of a changing climate and increasing urbanization.