Can enhanced three-outlet diversion and joint lake-outlet regulation mitigate droughts in Dongting Lake, China?

Study region Dongting Lake (DTL), China. Study focus DTL, the second-largest freshwater lake in China and an internationally important wetland, has experienced increasingly severe droughts over the past two decades, posing serious threats to regional ecosystem stability and water supply security. Enhancing the diversion capacity of the three Yangtze River outlets to increase inflow to DTL has been proposed as a potential drought-mitigation measure. However, its effectiveness, potential adverse impacts, and synergy with other regulation strategies remain poorly quantified. To address these gaps, this study couples a hydrodynamic model with a two-stage hierarchical model proposed herein to systematically assess drought responses in DTL to enhanced three-outlet diversion and, for the first time, to quantitatively evaluate the drought-mitigation effectiveness and spatial complementarity of its joint implementation with a planned lake-outlet water-level regulation project. New hydrological insights The results indicate that (1) increasing diversion capacity markedly raises water levels in the West–South connecting channel, most areas of South DTL, and parts of the main drainage channel in East DTL, while slightly lowering water levels at the lake outlet and adjacent shallow areas. Accordingly, drought-mitigation effectiveness exhibits a pronounced spatial gradient, gradually weakening from West DTL to South DTL and then to East DTL. (2) Joint regulation effectively offsets lake-outlet water-level declines induced by enhanced diversion alone and substantially reduces drought duration, severity, and intensity at the lake-wide scale. Moreover, the two measures exhibit strong spatial complementarity: lake-outlet water-level regulation mainly mitigates droughts in East DTL and eastern South DTL, whereas West DTL and most areas of South DTL benefit primarily from enhanced three-outlet diversion. This study provides quantitative and mechanistic insights into coordinated drought management for DTL.