Ephemeral Channel Expansion: Predicting Shifts Toward Intermittency in Vulnerable Streams Across Semi-Arid CONUS

Broad trends point to the slow drying of streams, with warming temperatures and altered precipitation fueling declines in discharge across the Western United States. Sustained reductions in streamflow have the potential to drive the expansion of non-perennial channel networks, yet this process remains poorly characterized, with limited understanding of the variables which control stream vulnerability to intermittency or the spatial and temporal extent of these shifts. This research identifies significant trends toward novel intermittency across semi-arid regions of CONUS from 1980 to 2024. Of the 483 stream gages analyzed, more than half demonstrated reductions in discharge and increases in the frequency and duration of flow cessation. The relationship between flow intermittency and physical, hydrologic, climatic, and agricultural variables was further explored through discriminant function analysis (DFA). The timing of wet-season moisture, specifically December and January precipitation, was identified as the primary factor controlling the development of intermittency in semi-arid zones. With forecasted reductions in precipitation across CONUS, many currently perennial systems are vulnerable to developing intermittency. As a result, intermittent flow regimes are projected to expand further into previously perennial streams, as well as exacerbate dry-down across vulnerable channels.