基于Copula函数的中国南方干旱风险特征研究

Characteristics of drought risk in southern China based on the Copula function

  • 摘要: 为了准确认识和分析与旱灾致灾因子危险性相关的干旱特征变量,利用中国南方96个气象站1961—2012年逐月降水资料,基于Clayton、Frank、Galambos、Gumbel以及Plackett Copula函数,建立了服从威布尔分布的干旱历时、服从对数正态分布的干旱严重程度两个相关特征变量的联合分布模型,择优使用Frank Copula函数计算了中国南方干旱条件概率与条件重现期,比较分析了该区域干旱事件第1、第2联合重现期的空间分布特征。研究表明,干旱严重程度(干旱历时)的条件概率分布随着干旱历时(干旱严重程度)阈值的增大而减小;干旱严重程度(干旱历时)的条件重现期与干旱历时(干旱严重程度)阈值成正比。当干旱历时阈值为6个月、干旱严重程度阈值为6时,中国南方整体存在较大的干旱风险,研究区整体第1“且”(干旱历时和干旱严重程度均超过给定阈值)联合重现期平均为4.8 a,第1“或”(干旱历时和干旱严重程度有一个超过给定阈值)联合重现期平均为2.6 a,第2“或”联合重现期平均为3.5 a。当干旱历时阈值为9个月、干旱严重程度阈值为13.5时,研究区整体第1“且”联合重现期平均为12.6 a,第1“或”联合重现期平均为4.7 a,第2“或”联合重现期平均为7.7 a。中国南方的干旱高风险的区域主要位于四川盆地、贵州东北部、广西北部、广东西部以及云南大部分地区;低风险的区域主要位于四川西北部,四川、云南、贵州三省交汇区以及广东中部地区。

     

    Abstract: For accurate understanding and analysis of drought characteristics associated with drought hazard, based on the monthly precipitation data of 96 weather stations in southern China from 1961 to 2012, five candidate Copula models of Frank, Clayton, Galambos, Gumbel and Plackett Copula, were used for constructing the joint distribution function of drought characteristics, namely duration and severity. The drought duration follows the Weibull distribution and the drought severity follows the Lognormal distribution.It is found that for the study region, the Frank Copula is the best fitted Copula model compared to the others. Subsequently the conditional probability, conditional return period and spatial joint return period of droughts were also investigated, based on the derived Copula-based joint distribution. The results indicated that, the conditional drought severity distribution is decreased if the drought duration exceeds various thresholds, and so does the conditional drought duration distributions if the drought severity exceeds various thresholds. Both imply that the conditional drought severity distribution and the conditional drought duration distribution are decreased with the increasing drought duration and drought severity, respectively.The conditional return period of drought severity is directly proportional to the duration thresholds, the conditional return period of drought duration is directly proportional to the severity thresholds.Given that the drought duration is 6 months with a drought severity of 6, the primary "and" (viz., both drought duration and drought severity are larger than prescribed thresholds) average joint return period is 4.8 a, the primary "or" (viz., either drought duration or drought severity exceed given thresholds) average joint return period is 2.6 a, and the second "or" average joint return period is 3.5 a.Given that the drought duration is 9 months with a drought severity of 13.5, the primary "and" average joint return period is 12.6 a, the primary "or" average joint return period is 4.7 a, and the second "or" average joint return period is 7.7 a. A high risk can be detected in the Sichuan Basin, the northeastern Guizhou Province, northern Guangxi Province, western Guangdong Province and a larger part of Yunnan Province, and a relative lower drought risk is observed in the northwest of Sichuan Province, the junction of Sichuan with Yunnan and Guizhou Provinces, and the middle parts of Guangdong Province.

     

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