Reservoir operation affects propagation from meteorological to hydrological extremes in the Lancang-Mekong River Basin

Hydrological extremes intensified by meteorological extremes are threatening water security in the Lancang-Mekong River Basin (LMRB), and reservoir operation may mitigate hydrological extreme through regulating hydrological pro-cesses during meteorological extreme. However, the capacity of reservoirs in modulating propagation from meteoro-logical extremes to hydrological extremes has seldom been quantified. This study adopted the VIC-Reservoir hydrological model to assess the impact of reservoir operation on the propagation at multi-timescales in the LMRB. The Standardized Precipitation Index and Standardized Streamflow Index were adopted to characterize meteorologi -cal extreme and hydrological extreme, respectively, on a range of timescales. The results indicate that reservoir oper-ation has effectively delayed the propagation from meteorological to hydrological extremes during the period of 2008-2016 with rapid reservoir development in the LMRB, compared with the period of 1984-2007 with natural con-dition. The transmission process of extreme events with a duration of no more than 6 months has been suppressed dur -ing the reservoir impact period. However, the influence of reservoir regulation on long-term extreme events that last more than 12 months is generally low. In the upstream basin where reservoir impact is largest, reservoirs can exert a weak mitigation effect on long-term dry extremes. This study provides quantitative assessment of the role of reservoirs in regulating propagation between meteorological and hydrological extremes in the LMRB, and facilitate decision making for the management of water hazards under changing environment.