Climate change and effectiveness of dams in flood mitigation in India

India is the third largest dam-building nation in the world. Dams are critical in irrigation, hydropower generation, and flood control. Observational evidence suggests that dams mitigated and caused floods in several river basins in India. However, the effectiveness of dams in flood mitigation and associated driving factors remain unexplored under the current and projected future climate. Using in-situ and satellite observations and simulations from hydrological and hydrodynamic models for 178 major dams, we show that major dams' effectiveness in flood mitigation in India depends more on the antecedent reservoir storage than precipitation variability in the river basins upstream of dams. Most floods in dams' downstream regions occur when reservoirs exceed 90% of their full capacity. Dams are more effective in mitigating floods in July than in the later part of the summer monsoon season. The number of days with reservoir storage over 90% of total capacity is projected to rise considerably under the warming climate, limiting dams' effectiveness in mitigating floods. The duration with reservoir storage exceeding 90% of the total capacity is projected to rise from ~ 6 days at 1°C to 23 at 3°C global warming levels, highlighting the need for climate change mitigation. The substantial rise in compound extremes of high inflow and high antecedent storage in the future under the warming climate will limit the effectiveness of dams in mitigating floods in India. Our findings highlight the need for more advanced approaches for dam operations integrated with early warning of extreme inflow and reservoir storage in India.