Baseflow dominates river flow during droughts across the global streamflow network

Hydrological droughts occur when rainfall shortages reduce water storage in catchments, leading to delayed and prolonged low-flow conditions. How strongly baseflow supports river flow during droughts and whether this buffering remains stable under climate warming remain uncertain across regions. Using global streamflow gauge observations, terrestrial water storage information, and CMIP6 simulations, we quantified the drought-sustained fraction (DSF), representing the fraction of drought-period streamflow contributed by baseflow, and the additive baseflow buffering index (BBI), which measures the departure from the climatological baseflow index (BFI). Under severe meteorological drought, 74.2% of stations showed a positive BBI, indicating stronger relative baseflow dominance, whereas 12.7% showed little change and 13.1% showed a decline in the baseflow fraction. BBI increased with low-flow severity and streamflow deficit, while baseflow retention declined, indicating that quickflow generally decreased more rapidly than baseflow. Present-day flow partitioning also constrained future slow-flow behavior, underscoring the importance of storage-release processes in sustaining river flow during drought. Baseflow contributions to river flow increase during drought relative to baseline conditions, highlighting the increasing importance of groundwater-supported flow as drought severity intensifies, according to a study that combines global streamflow records, satellite observations, and CMIP6 simulations.