Summer floods have always been a major challenge for people living in the Brahmaputra river basin in Northeast India. At the same time, the Brahmaputra River is the backbone of the region's resource-based economies and livelihoods. Riverine communities in the region rely upon a variety of adaptation strategies to cope with recurrent floods, but climate change impacts are testing their resilience and adaptive capacity to floods by increasing their severity. At the same time, a multitude of new dams are under construction in Northeast Arunachal Pradesh along the Brahmaputra River and its tributaries in an effort to meet India's growing energy demands. Using a case study dam and household-level interview data, this research examines how large-scale hydropower development efforts in Arunachal Pradesh shape the capacity of downstream communities to adapt to floods. Results showed that, by prioritizing hydroelectricity production over flood protection, large dams along the Brahmaputra are eroding the adaptive capacity of downstream communities to summer floods, at the same time as climate change impacts are exacerbating the flood risk. As dams and climate change jointly make the floodplains of Northeast India increasingly hazardous, many are likely to relocate and shift livelihoods away from agriculture and towards daily wage labor.