Abstract Hydrological whiplash refers to rapid transitions between low flows (referred to here as droughts) and floods, typically occurring at sub-seasonal timescales. This phenomenon has emerged as a critical hydroclimatic risk, posing serious challenges to water resources management and infrastructure resilience. However, the spatiotemporal characteristics of hydrological whiplash and their drivers remain poorly understood. Here using daily mean discharge data from 2,212 streamflow stations across the contiguous United States during 1951–2024, we identify 13,661 drought-to-flood and 4,721 flood-to-drought events. We find drought-to-flood transitions occur more frequently, over shorter transition periods, and with greater intensity than flood-to-drought transitions, with the former predominantly occurring in autumn and winter, and the latter in summer. Both whiplash types exhibit predominant decreasing trends in frequency over the past seven decades, consistent with the declining occurrences of drought. The negative trend contrasts with that of hydroclimatic whiplash characterized solely based on precipitation anomalies, highlighting the essential role of watershed functions (e.g., partition, storage, and release) in modulating discharge variability. Divergent trends between near-natural and human-regulated watersheds further highlight that reservoir operations could be a key modulator of hydrological whiplash dynamics. Our findings underscore the importance of incorporating human and watershed processes into future assessments of hydroclimatic extremes under a changing climate.