东江流域气象干旱向水文干旱传递阈值研究

Study on the Transfer Threshold from Meteorological to Hydrological Drought in Dongjiang River Basin

对不同干旱类型之间传递阈值研究可有效分析干旱传递的发生规律和机理,特别是对气象干旱向水文干旱传递阈值的研究。以东江流域为研究对象,计算月尺度的标准化降水指数SPI和标准化径流指数SRI,并基于游程理论识别干旱事件,提取干旱事件及其特征,包括干旱历时和干旱烈度。对发生时间全部或部分重叠的气象干旱事件和水文干旱事件进行匹配。对匹配后的干旱特征属性进行边缘分布拟合,验证气象干旱和水文干旱的历时或烈度之间的相关性,基于二变量Copula函数分别建立气象干旱与水文干旱特征的联合分布模型,计算不同气象干旱条件下不同等级水文干旱(中旱、重旱、极旱)发生的条件概率,取条件概率为0.95时对应的气象干旱历时或烈度值,作为气象干旱向该等级水文干旱传递的干旱历时(烈度)阈值。结果表明:东江流域气象干旱历时和烈度的最优拟合函数均为伽玛分布,水文干旱历时的最优拟合函数为伽玛分布,水文干旱烈度的边缘分布函数为广义正态分布。Gumbel-copula函数拟合干旱历时和烈度的效果较好。东江流域中旱、重旱、极旱等级的干旱历时传递阈值分别为6.9、8.3、9.4个月;干旱烈度的传递阈值分别为4.6、5.7、6.6。干旱传递阈值可以为水文干旱的预测以及防旱减灾的决策提供参考。

The study on transfer threshold between different drought types can effectively analyze the occurrence law and mechanism of drought transfer,especially the study on transfer threshold from meteorological drought to hydrological drought.Taking the Dongjiang River Basin as the research object,this paper calculates the standardized precipitation index(SPI)and the standardized runoff index(SRI)at month scale,identifies and extracts the drought events and their characteristics,including drought duration and drought severity based on the run theory,matches the meteorological drought events and hydrological drought events that occur at the fully or partially same time,fits the edge distribution of the matched drought characteristic attributes to verify the correlation between the duration or severity of meteorological and hydrological droughts,establishes the joint distribution models of meteorological drought and hydrological drought based on two-variable Copula function,calculates the conditional probability of different grades of hydrological drought(moderate drought,severe drought and extreme drought)under different meteorological drought conditions,and takes the drought duration or severity value corresponding to the conditional probability of 0.95 as the drought duration or severity threshold for the transfer of meteorological drought to the hydrological drought of this grade.The results show that:The optimal fit functions of meteorological drought duration and severity in the Dongjiang River Basin were gamma distribution.The optimal fit function of hydrological drought duration is gamma distribution,and the marginal distribution function of hydrological drought severity was generalized normal distribution.The drought duration and severity were better when fitting by the Gumbel-copula function.The thresholds of drought duration of middle,severe and extreme drought grades in Dongjiang River basin were 6.9 months,8.3 months,9.4 months,respectively.While the thresholds of drought severity were 4.6,5.7 and 6.6,respectively.Drought transfer threshold can provide reference for hydrological drought prediction and government decision-making of drought prevention and mitigation.