Based on the Standardized Precipitation Index (SPI) and copula function, this study analyzed the meteorological drought in the upper Minjiang River basin. The Tyson polygon method is used to divide the research area into four regions based on four meteorological stations. The monthly precipitation data of four meteorological stations from 1966 to 2016 were used for the calculation of SPI. The change trend of SPI1, SPI3 and SPI12 showed the historical dry-wet evolution phenomenon of short-term humidification and long-term aridification in the study area. The major drought events in each region are counted based on SPI3. The results show that the drought lasted the longest in Maoxian region, the occurrence of minor drought events was more frequent than the other regions. Nine distribution functions are used to fit the marginal distribution of drought duration (D), severity (S) and peak (P) estimated based on SPI3, the best marginal distribution is obtained by chi-square test. Five copula functions are used to create a bivariate joint probability distribution, the best copula function is selected through AIC, the univariate and bivariate return periods were calculated. The results of this paper will help the study area to assess the drought risk.

中文翻译：

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基于Copula函数的岷江上游气象干旱双变量频率

本研究基于标准化降水指数（SPI）和copula函数，对岷江上游流域的气象干旱进行了分析。泰森多边形法基于四个气象站将研究区域划分为四个区域。SPI计算采用4个气象站1966-2016年月降水数据。SPI1、SPI3和SPI12的变化趋势显示了研究区短期加湿和长期干旱的历史干湿演化现象。各地区主要干旱事件均基于SPI3进行统计。结果表明，茂县干旱持续时间最长，小旱事件发生频率高于其他地区。九个分布函数用于拟合基于SPI3估计的干旱持续时间（D）、严重程度（S）和峰值（P）的边际分布，通过卡方检验得到最佳边际分布。五个copula函数被用来创建一个双变量联合概率分布，通过AIC选择最佳copula函数，计算单变量和双变量返回周期。本文的研究结果将有助于研究区评估干旱风险。