基于多维Copula函数的澜沧江-湄公河流域气象干旱特征分析

Analysis of meteorological drought characteristics in the Lancang-Mekong River Basin based on multi-dimensional Copula function

为全面揭示变化环境下澜湄流域多维气象干旱特征,采用标准化降水蒸散指数SPEI表征流域气象干旱,基于游程理论分别提取澜沧江段和湄公河段上、中、下游流域1901—1960年和1961—2021年两个时段的干旱事件,利用Copula函数分别构建两个时段不同子流域二维和三维干旱特征变量联合分布,计算不同干旱特征变量组合条件下的干旱联合发生概率,对比分析不同子流域多维气象干旱特征的时空变化。结果表明:时间上,1961—2021年各子流域平均干旱程度均较1901—1960年更严峻,尤其是极端干旱事件(单变量累积频率为25%、50%)的多维干旱联合发生概率增幅最大;空间上,1961—2021年,随着干旱历时、烈度和烈度峰值的增加,“或”情况下多维干旱联合发生概率最高值区自北向南转移,“且”情况下多维干旱联合发生概率最高值区自南向北转移。

In order to comprehensively unveil multidimensional meteorological drought characteristics of the Lancang-Mekong River Basin under changing environments,the standard precipitation evapotranspiration index(SPEI)was used to characterize meteorological drought in the basin.Drought events in the Lancang River and the upper,middle,and lower reaches of the Mekong River during 1901-1960 and 1961-2021 were extracted based on the run theory,and two-dimensional and three-dimensional drought characteristic variable joint distributions for different sub-basins in the two periods were constructed using the Copula function.Through the calculation of the drought joint occurrence probabilities under different combinations of characteristic variables,the spatio-temporal changes in multidimensional meteorological drought characteristics in different sub-basins were compared and analyzed.The results show that in terms of time,the average drought severity of each sub-basin during 1961-2021 was higher than that during 1901-1960,especially the joint occurrence probabilities of extreme drought events(with univariate cumulative frequencies of 25%and 50%)increased the most.In terms of space,during 1961-2021,with the increases in drought duration,drought intensity,and drought peak intensity,the area with the highest value of multi-dimensional drought joint occurrence probabilities in the“or”case shifted southward from north,while in the“and”case,it shifted northward from south.