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基于Vine Copula的非一致性水文干旱动态风险评估模型

Model for estmating non-consistency hydrological drought dynamic risks based on Vine Copula

  • 摘要: 当前非一致性水文干旱研究多聚焦于指数构建与干旱特征分析,干旱风险评估模型的研究相对有限。该研究以绿洲农业为主导的和田河流域为研究对象,采用平稳性检验分析径流序列非一致性特征;基于广义可加模型耦合气候变化(降水、气温和蒸散发)和人类活动(水库指数、取用水)构建非一致性标准化径流指数(non-consistent standardized runoff index,NSRI),并与标准化径流指数(standardized runoff index,SRI)对比验证其适用性;结合游程理论和Vine Copula构建耦合干旱特征变量与发生概率的非一致性水文干旱动态风险评估模型。结果表明:1)流域径流序列呈现非一致性特征,表明该流域径流过程受气候变化和人类活动显著影响;2)NSRI在干旱事件表征方面较SRI更为准确,更适用于和田河流域水文干旱监测;3)和田河流域整体处于中风险状态,玉龙喀什河风险均值0.308、喀拉喀什河风险均值0.306均位于中风险区间,经1991—1992年典型干旱事件验证,模型具有较好的预警能力。基于Vine Copula的非一致性水文干旱动态风险评估模型能够有效识别和预警和田河流域水文干旱事件,研究成果可为流域水文干旱监测、农业灌溉用水调度及绿洲农业干旱风险预警提供科学依据。

     

    Abstract: Hydrological drought has posed serious threats to water security in the arid and semi-arid regions. Particularly, the surface water resources are already scarce in the typical oasis areas in the Hotan River Basin of the southern Xinjiang Uygur Autonomous Region in China. However, the water demands have expanded to cause a non-consistent pattern in the hydrological regime of the basin under climate change. The conventional consistency assumption on the hydrological drought is also limited in the large-scale production of sustainable agriculture. Previous research has also focused on the non-consistent drought indices and drought features under changing conditions. It is often required to accurately assess the dynamic drought risk for agricultural planning and water resources. In this study, a dynamic risk assessment framework was developed for the non-consistent hydrological drought in the Hotan River Basin. The runoff series was selected to examine the non-consistent features using statistical testing. Empirical evidence was then provided for the impacts of environmental changes on the hydrological process. The Generalized Additive Models for Location, Scale, and Shape (GAMLSS) framework was employed to construct a non-consistent standardized runoff index (NSRI). Distribution parameters were explicitly incorporated with the time-varying influences of the climatic factors and anthropogenic activities. Consistent drought indices were avoided to validate the superiority of the framework. The NSRI was systematically compared against SRI using drought characteristic analysis and historical drought events. Better performance was achieved in capturing the drought severity, in agreement with actual disaster occurrences. Multiple drought features were integrated with the occurrence probabilities under non-consistent conditions using the Vine Copula method. The high-dimensional joint distributions were decomposed into a series of conditional bivariate copulas, effectively reducing the complex parameter estimation and the complex dependencies among different drought attributes. The drought risk was quantified as more actionable information using continuous, time-varying metrics rather than a static value. The performance was validated using well-documented historical drought events, indicating reliable early warnings. Some insights were obtained. Firstly, there was a significant variation in the hydrological regime, where the non-consistent features of the runoff series were attributable to both climatic shifts and human interventions. Secondly, the superior performance of the NSRI was achieved in capturing the drought events, compared with the SRI. More accurate characterization of drought severity resulted in better agreement with the documented drought occurrences. Thirdly, the risk assessment indicates that the basin is currently subjected to moderate drought risk levels, where both major tributaries share similar risk profiles. The effectiveness of the model was validated to identify the high-risk periods, according to the typical drought events in 1991-1992. Timely warnings were provided for both scientific and practical applications. Non-consistent hydrological drought analysis was integrated with the GAMLSS index with Vine Copula-based dynamic risk assessment in a unified framework. The model can be readily adapted to similar regions under hydrological conditions. The finding can provide valuable support for drought monitoring, agricultural irrigation, and risk management in the oasis agricultural regions. Non-consistent hydrological drought can also offer a robust framework to enhance the drought resilience in the water-stressed regions under environmental conditions in sustainable agriculture.

     

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