Subsurface conditions and hydrologic accumulation drive stream connectivity and flow intermittency in urban river networks

Hydrological alteration and climate change are making urban rivers drier and more intermittent, but limited understanding of urban stream network dynamics prevents effective, context-specific management. We determined how urban land cover, subsurface characteristics, and weather collectively control stream network connectivity and flow intermittency in the Little Calumet River Watershed, USA. Contrary to prevailing expectations, headwater tributaries with greater impervious cover were more persistent, while tributaries with greater prevalence of permeable soils and paleo-sand deposits were more intermittent, underscoring the importance of subsurface conditions for urban stream connectivity. Active network drainage length was best correlated with antecedent effective precipitation at six days, indicating that these urban headwater systems expand primarily through hydrologic accumulation rather than immediate runoff. These observations challenge prevailing assumptions about fundamental drivers on urban stream connectivity. Our findings show how hydrometeorological, land surface, and subsurface conditions jointly control network dynamics, offering a foundation for building urban watershed resilience. Urban headwaters with less impervious cover are more intermittent due to infiltration in permeable soils, while stream network expansion follows hydrologic accumulation, as revealed by hydrologic observations and modeling in the Little Calumet River Watershed, USA.