To evaluate the capacity of a reservoir system operated presently in the Sishui River System of Dongting against historical extreme floods

this study develops a VIC-WUR distributed hydrological model coupled with a reservoir operation module. This model simulates and compares the 1954 basin-wide catastrophic flood events under the scenarios with and without reservoir regulation. The results demonstrate the reservoir group generates significant attenuation to flood peaks

with a maximum peak flow reduction of 62.5% (the Zaoshi Reservoir on the Lishui River)

and the longest peak lag of 177.0 hours. The regulatory efficacy features significant spatial variations

subject to the storage capacity

geographical location

and coordinated operation. In the joint operation case of the Zaoshi and Jiangya reservoirs on the Lishui River

the average peak reduction rate is increased up to 56.6%. This study reveals quantitatively the spatiotemporal regulation patterns of reservoir groups against extreme floods

laying a basis critical for managing flood risks in the middle Yangtze and decision making of its collaborative reservoir operation.