The Drought Probability Analysis in the Upper and Middle Reaches of the Yangtze River Basin Based on Copula Function

受气候变化和强人类活动影响，长江流域年际和年内干旱频发，给长江经济带建设带来严峻挑战，干旱概率分析为把握应对极端天气挑战的主动权提供科学依据。本研究基于长江流域上中游气象站点和水文站点的实测数据以及ERA5数据集，通过标准化降水指数和标准化降水蒸散指数识别了气象干旱事件，并运用Copula函数构建气象–水文联合分布模型，系统解析了长江流域上中游地区气象干旱与水文干旱的联合概率分布特征。结果表明：长江流域上中游的气象干旱发生频率较高，干旱概率为25%~40%；气象干旱与水文干旱的联合概率在夏季最为显著，尤其是在岷江、乌江等流域，夏季的气象水文联合干旱概率达到峰值，夏季降水量减少与径流量下降之间相关性最为显著。两种干旱指标在长江流域上中游的表现一致性较好，自2006年后识别出的干旱事件明显增多，SPI和SPEI识别年均干旱事件次数较2006年之前分别增加了16次和17次。本研究揭示了长江流域上中游干旱发生规律，可为流域抗旱减灾策略的科学制定和水资源优化配置提供基础支撑。Due to the impacts of climate change and intense human activities, interannual and seasonal droughts in the Yangtze River basin have become frequent, posing severe challenges to the construction of the Yangtze River Economic Belt. Drought probability analysis provides a scientific support for taking proactive measures to address the challenges of extreme weather. This study identified meteorological drought events based on measured data from meteorological and hydrological stations in the upper and middle reaches of the Yangtze River Basin, as well as the ERA5 dataset, using the standardized precipitation index and standardized precipitation evapotranspiration index. It also employed Copula functions to construct a meteorological-hydrological joint distribution model, systematically analyzing the joint probability distribution characteristics of meteorological and hydrological droughts in the study area. The results indicate that the frequency of meteorological droughts in the sub-basins of the upper and middle reaches of the Yangtze River basin is relatively high, with drought probabilities ranging from 25% to 40%. The joint probability of meteorological and hydrological droughts is most significant in the summer, especially in the Min River and Wu River basins, where the joint drought probability reaches its peak during this season. Additionally, the correlation between reduced summer precipitation and decreased runoff is most pronounced. The two drought indices (SPI and SPEI) exhibit good consistency in the upper and middle Yangtze River basin. Since 2006, the number of identified drought events has significantly increased, with the annual average number of drought events identified by SPI and SPEI increasing by 16 and 17 times, respectively, indicating an intensification of drought conditions. The findings not only contribute to revealing the drought occurrence patterns in the upper and middle reaches of the Yangtze River basin but also provide a hydrological foundation for the scientific formulation of regional drought mitigation strategies and the optimal allocation of water resources.