Four Decades of Baseflow Drought Analysis Reveals Varying Contributions of Climatic Drivers and Physical Controls

While the impacts of subsurface fluxes on mediating hydrologic response to droughts are often ignored, several studies indicate that baseflow can sustain rivers during droughts and decrease the vulnerability of water supplies. Therefore, given the increasing impacts of droughts on economic and environmental issues, understanding the baseflow drought (BFD) evolution and its drivers are critical. In this study, we quantify and analyze the long-term evolution of BFD characteristics across the Contiguous United States. We use long-term daily baseflow values of DeepBase data set and explainable machine learning models to identify and rank the climatic and physical drivers of BFD. Our analysis reveals notable regional disparities in BFDs, with western regions, particularly the Southwest, experiencing increased frequency and prolonged durations, while much of the eastern areas show declining trends. During the past decade, BFD frequency has been governed mainly by anomalies in the atmospheric water balance and by soil properties. Its duration has been primarily influenced by hydrogeologic attributes, and its intensity has been modulated most strongly by topographic setting. Highlighting the non-stationary and complex nature of BFD mechanisms, our results have practical implications for water resource management and drought adaptation strategies.