基于Copula函数的松花江流域水文干旱频率分析

[目的]基于Copula函数对松花江流域进行水文干旱频率分析.[方法]利用可变阈值法识别日尺度水文干旱事件的历时和烈度,并进行融合处理;选择6种常用的分布函数拟合干旱特征变量,以Kolmogorov-Smirnov检验法优选单变量边缘分布;从3种Copula函数中优选函数模型,建立了干旱历时和烈度二维联合分布,并计算联...

Using Copula Method to Analyze Drought Frequency in Songhua River Basin

【Background】Drought could significantly impact hydrological processes and water resources,and understanding frequency and uncertainty of drought occurrence is hence imperative to water resources planning.The copula method has emerged as an improved multivariate analysis over the univariate analysis for quantitative analysis of drought.【Objective】This paper isto present the results of the frequency and severity of droughts in Songhua river basin calculated using thecopula multivariate method.【Method】The analysis was based on archived data,and duration and severity of the pooled daily drought events were identified using the variable threshold level method.The drought index variables were fitted by sixcommon distribution functions respectively,and they were then evaluated using the Kolmogorov Smirnov test method.Optimal modelselected from three Copula functions was used toestablisha two-dimensional joint distribution for the drought index variables,from which we calculatedthe joint distribution probability as well as the return period.The uncertainty of the drought was analyzed using the Monte Carlo method.【Result】Withthe pooling criteria set to be p_c=0.1 and t_c=5,the average drought duration was 81~105 days in the basin.The lognormal distribution can adequately describe the marginal distribution of the drought durationin Dalai,Fuyu and Harbin stations in the basin,despite the differences in optimal distribution of the drought severity between them.The Frank copula was the best model for the two-dimensional joint distribution of the drought,and the return periods of the droughts were less than 20 years.When the return period was 20 years,the maximum design values for Dalai,Fuyu,Harbin and Jiamusi hydrological stations were most uncertain.【Conclusion】The copula multivariate model can adequately describe the joint distribution of the drought index variables in Songhua river basin,and its application should consider drought uncertainty.