Controls and Predictability of Large Floods in the Brahmaputra River Basin

The Brahmaputra River Basin is among the most flood-prone regions globally, experiencing recurrent large floods with severe socio-economic and ecological impacts. Despite extensive flood management interventions, forecasting skill remains limited due to the basin’s complex hydrology, strong monsoon variability, and pronounced land–atmosphere interactions. This study investigates the drivers and dynamics of large floods in the Brahmaputra Basin, with a particular emphasis on coupled land–atmosphere processes. We conduct a composite analysis of major flood events using reanalysis datasets, satellite observations, and hydrological records. Our results show that large floods are consistently associated with anomalously high atmospheric moisture content, extreme and spatially extensive precipitation, and elevated antecedent soil moisture that amplifies runoff generation. The concurrence of saturated catchments with persistent multiday monsoon rainfall leads to rapid escalation of flood magnitude and prolonged flood duration. In addition, enhanced moisture transport into the basin emerges as a critical contributor to the development of large flood events. By integrating these insights into coupled land–atmosphere modeling frameworks, we demonstrate that improved representation of soil moisture dynamics, rainfall persistence, and moisture transport pathways can substantially enhance flood predictability. This work advances the understanding of flood-generating mechanisms in monsoon-dominated river basins and provides actionable insights for improving early warning systems and adaptive flood risk management in the Brahmaputra Basin.