基于Copula函数的宜昌水文干旱特征分析

Analysis of Hydrological Drought Characteristics in Yichang Based on Copula Function

基于宜昌站1951~2014年的实测月径流资料,选用标准化径流指数(SSI),运用游程理论识别干旱,应用Copula函数构建干旱特征变量间的多维联合概率分布,进而对宜昌站的干旱特征进行分析。结果表明:(1)宜昌在1950~1980年代,干旱次数呈现交替变化,自1990年代以来,特别是进入21世纪后,宜昌干旱事件增多、持续时间增大、干旱烈度和峰值增高,干旱情势有加重的趋势;(2)Copula函数可很好地描述宜昌地区干旱特征变量间的联合概率分布,多变量的联合重现期和同现重现期可分别作为实际单变量重现期区间估计的下限和上限,用以评估宜昌地区不同干旱变量值所代表的干旱事件发生的频率;(3)宜昌站近60年出现两次严重的干旱事件,一次发生于1978年9月~1979年7月,该事件的干旱历时和干旱烈度均达到了历史极值,这两个变量的联合重现期约为32a,同现重现期约为110a;该事件的干旱历时、干旱烈度和烈度峰值三个变量的联合重现期为9a,同现重现期约为115a。另一次干旱事件发生于2006年6月~12月,其烈度峰值达到了历史极值,其重现期接近90a;该次事件的干旱历时、干旱烈度和烈度峰值三者的联合重现期只有13a左右,同现重现期则超过了231a。

Based on the measured monthly runoff data at the Yichang Station during 1951-2014,this paper adopted the standardized runoff index(SSI)and run-length theory to identify drought,and made used of the Copula function to construct a multi-dimensional joint probability distribution between drought characteristic variables.The analysis results show that:(1)Yichang experienced alternating changes in the number of droughts from the 1950s to the 1980s.Since the 1990s,especially after entering the 21st century,the increase in the duration of drought events in Yichang has increased the severity of droughts and peaks.There is a tendency of aggravation;(2)Copula function could well describe the joint probability distribution between drought characteristic variables in Yichang region,and the multivariate joint return period and coincident return period can be used as actual univariate recurrence interval estimates.The lower and upper limits were used to evaluate the frequency of drought events represented by different values of drought variables in Yichang;(3)Two severe drought events occurred at the Yichang Station in the past 60 years,one occurred from September 1978 to July 1979.In March,the drought duration and drought intensity of the event reached historical extreme.The joint return period of these two variables is about 32 years and the coincident return period is about 110 years.The drought return period is 9 years,and the coincident return period is about 115 years.Another drought event occurred from June to December 2006,and its peak intensity reached historical extreme.Its return period is close to 90 years;joint return period of the drought drought and peak intensity of the event is only about 13 years,and the coincident return period exceeds 231 years.