Abstract: The construction and operation of the Three Gorges Project (TGP) have significantly altered the hydrological regime of the middle and lower reaches of the Yangtze River, thereby impacting irrigation water supply. This study focuses on analyzing the effects of TGP operation on the safety of irrigation water supply in the Poyang Lake areas, specifically considering water quantity and fulfillment of water supply. To achieve this, the evolution of water resources and the situation of water supply before and after TGP operation were investigated. Following the operation of TGP, the Poyang Lake witnessed a decreasing trend in available water supply, with the most significant reductions occurring in September and October during impoundment periods. Moreover, the overall water level in the lake area has dropped by 1.1-2.5 meters. Although the total water quantity can still meet irrigation and water supply demands, there is a noticeable decline in the fulfillment of both irrigation and water supply requirements in urban and rural regions, leading to a significant increase in total water shortage. The fulfillment of secured rural and urban water supply and irrigation water supply requirements has dropped from 99.1% and 83.6% before TGP operation to 87.5% and 42.7% after operation, respectively. Simultaneously, water shortage for rural and urban water supply and irrigation water supply has increased from 0.78 and 70.32 to 93.85 and 186.11 million cubic meters, respectively. However, it is worth mentioning that early or delayed impoundment of TGP can slightly mitigate the project’s influence on water supply and irrigation during impoundment, thereby increasing the water supply capacity by 0.2% and 0.3% respectively.

Key words: modified hydrological regime, irrigation safety, water supply safety, Three Gorges Project, Poyang Lake