Hydrological droughts have caused greater damage due to climate change and rapid socio-economic development. Exploring future hydrological drought variations is imperative for drought defense and infrastructure construction. This study aims to investigate future changes in hydrological droughts across the Yangtze River Basin during 2025 ∼ 2100. The Distributed Time-Variant Gain Model coupled with the Standard Operation Policy module (DTVGM-SOP) was employed to project future runoff driven by the bias-corrected Coupled Model Intercomparison Project Phase 6 (CMIP6) data. Subsequently, future spatial–temporal changes in the characteristics of hydrological droughts were analyzed based on the Standardized Runoff Index (). Lastly, future changes in the probability of concurrent hydrological droughts were evaluated using the bivariate copula functions. Results show that: (1) The DTVGM-SOP model can satisfactorily simulate monthly streamflow with a high Nash-Sutcliff Efficiency () of 0.75 ∼ 0.92. Future annual maximum discharge and annual average discharge in the mainstream and the northern tributaries are expected to increase by 3.34%∼58.19% and 3.11%∼32.66% respectively, while annual maximum discharge in the southern tributaries decreases by 0.54%∼20.09%. (2) The future annual and seasonal hydrological drought frequency is expected to decrease in most regions, while the frequency in spring increases in the Qinghai Tibet Plateau. The duration and severity of future hydrological droughts are expected to decrease by 9.52%∼78.69% and 5.13%∼81.36% in the whole basin except the source area and the Yalong River Basin. (3) Future concurrent hydrological droughts will be mitigated with decreasing frequency. The probability of concurrent hydrological droughts is expected to decrease by 46.15%∼96.47%, while future changes in the conditional probability of the mainstream are diverse in different concurrent scenarios with a range of −93.41%∼40.09%. The findings are helpful to improve the understanding of future hydrological drought variations in the Yangtze River Basin and provide essential information for damage reduction.

中文翻译：

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长江流域水文干旱未来变化：识别、时空特征及并发概率

由于气候变化和社会经济快速发展，水文干旱造成的损失更大。探索未来水文干旱变化对于抗旱和基础设施建设至关重要。本研究旨在调查2025年~2100年长江流域水文干旱的未来变化。采用分布式时变增益模型与标准运算政策模块（DTVGM-SOP）相结合来预测由偏差驱动的未来径流修正了耦合模型比对项目第 6 阶段 (CMIP6) 数据。随后，基于标准化径流指数（）分析了未来水文干旱特征的时空变化。最后，使用双变量 copula 函数评估了并发水文干旱概率的未来变化。结果表明： (1) DTVGM-SOP 模型能够很好地模拟月流量，Nash-Sutcliff 效率 () 高达 0.75 ∼ 0.92。预计未来干流和北部支流年最大流量和年平均流量将分别增加3.34%～58.19%和3.11%～32.66%，南部支流年最大流量减少0.54%～20.09%。 （2）预计未来大部分地区年季水文干旱频率将减少，青藏高原春季水文干旱频率将增加。预计未来除源区和雅砻江流域外的全流域水文干旱持续时间和严重程度将分别减少9.52%～78.69%和5.13%～81.36%。 （3）未来并发水文干旱将随着频率的减少而减轻。预计并发水文干旱的概率将下降46.15%∼96.47%，而未来主流条件概率的变化在不同并发情景下是不同的，范围为-93.41%∼40.09%。研究结果有助于提高对长江流域未来水文干旱变化的认识，为减轻损失提供重要信息。