Meltwater markedly exacerbates socioeconomic exposure to floods in the eastern Himalaya

Abstract Flood hazards across high mountain Asia present pronounced complexity due to the combined influence of rainfall, meltwater, and glacial lake outburst floods (GLOFs). The eastern Himalayan Brahmaputra basin is a critical hotspot of this integrated risk. However, a basin-wide quantification of the individual contributions of these drivers to flood exposure has been lacking. Here, we employ a calibrated coupled hydrological–hydraulic model to provide the first comprehensive assessment. We show that meltwater (snow and glacier melt) contributions to annual maximum floods increase with altitude. At the basin scale, meltwater amplifies population and gross domestic product (GDP) exposure to flooding by 1.3% and 1.5%, respectively. This amplification rises dramatically to 27.9% for population and 33.3% for GDP in high-altitude regions (⩾2000 m). Rainfall-derived discharge constitutes the dominant source of flood exposure, followed by meltwater; GLOFs present the least contribution. Nonetheless, GLOFs increase basin-wide population and GDP exposure by 1.2% and 1.3%, and notably intensify to 31.1% and 33.5% above 2000 m. Our findings deliver critical insights for developing targeted flood management strategies in the Brahmaputra basin.