Understanding Drivers of Baseflow Changes and Their Role in Hydrological Droughts

Hydrological droughts are often viewed through the immediate lens of atmospheric droughts, driven by precipitation deficits and evaporative demand. However, these droughts can be exacerbated by the long-term impacts of baseflow changes, which alter groundwater-fed streamflow critical for sustaining hydrological systems during prolonged dry periods. This study employs a global dataset of 7,138 catchments and the PCMCI+ causal discovery algorithm to unravel the spatiotemporal drivers of baseflow changes and their relationship with hydrological drought severity. We identify key climatic controls—precipitation, evaporative demand, and snow fraction—and quantify their influence across diverse climate zones. Precipitation emerges as the dominant driver globally (58.3% of catchments), while evaporative demand and snow fraction govern baseflows in tropical and polar regions, respectively. By mapping concurrent spatial occurrence in baseflow and hydrological drought, we delineate zones of critical risk where these processes overlap, exacerbating vulnerability to extremes. This study advances our understanding of spatiotemporal extremes and offers insights for improving the modeling and management of compound hydroclimatic events under climate change.