Reservoir storage flash droughts in India are driven by human interventions

• Precipitation changes in upstream catchments do not fully explain the long-term trends in reservoir storage. • Reservoir storage flash droughts (RFDs) are primarily driven by human interventions. • Small-sized (storage less than 1 BCM) reservoirs experience RFDs more frequently than large reservoirs. Reservoir storage flash droughts (RFDs), characterized by the rapid decline in reservoir storage, and conventional (long-term) reservoir storage droughts (RDs) impact water availability, hydropower generation, and agricultural activities. However, the mechanism and drivers of flash and conventional reservoir storage droughts in India remain unexplored. Using daily observations of reservoir storage, we identify RFDs and RDs in 81 major reservoirs in India during the 2000–2023 period. 46 out of 81 reservoirs are dominated by upstream climate as reservoir storage trends are driven by changes and variability in upstream precipitation, while the remaining 35 reservoirs are identified as human-dominating reservoirs. RFDs occur more frequently in human-dominating reservoirs than climate-dominating, especially in small reservoirs. About 70 % of RFDs in climate and human-dominating reservoirs are caused by sudden release to meet increased water demands in the downstream regions. Additionally, upstream precipitation deficit and downstream water demand control RDs, while downstream water demands can solely drive RFDs. Unlike reservoir storage trends, reservoir storage droughts are mostly linked with downstream water demands. We highlight the role of climate and human interventions in reservoir storage/droughts in India.