Impacts of the Three Gorges Reservoir on its immediate downstream hydrological drought regime during 1950–2016

Impacts of the Three Gorges Reservoir (TGR) on the downstream hydrological extremes always draw public attentions, particularly during its (quasi) normal water storing period. To investigate the impact of the TGR on its downstream hydrological drought regime during different operation stages, Yichang and Cuntan stations were selected as the case study site with Cuntan station as a reference. On the basis of the recent updated long-term flow discharge data series from 1950 to 2016, drought occurrence, duration and frequency of the hydrological droughts downstream of the TGR during pre- and post-dam periods were analyzed and compared, respectively. Abrupt changes were also identified for hydrological drought at different timescales. Results showed that TGR’s operation altered its downstream seasonal variation patterns of dry/wet spells, i.e., more severe drought from middle summer to middle winter while much wetter condition in late winter and spring; impacts on the downstream hydrological drought intensify with upgrading reservoir water storing levels; significant abrupt changes of hydrological droughts were identified, and the abrupt changing years were greatly correlated with the impoundment stages of the TGR. The study could provide valuable references for the ecological security and integrated water resources management of the Yangtze River basin and other large rivers severely impacted by anthropogenic activities over the world.