Copula based hydrological drought probability analysis in the Lake Dongting-catchment-Yangtze River system

Abstract

洞庭湖是长江中游重要的通江湖泊,水系格局复杂.近年来在气候变化和人类活动的双重影响下,江湖关系发生变化,湖泊水文干旱事件频发.基于洞庭湖、流域和长江干流水文站点的实测数据,通过标准化水位指数和标准化径流指数识别了水文干旱事件,并运用Copula函数分析了洞庭湖-流域-长江系统水文干旱的联合概率分布特征.结果表明:在年尺度上,1964—2016年间洞庭湖共发生了9次水文干旱事件,水文干旱的发生概率为14.01%,洞庭湖-流域系统、洞庭湖-长江系统的水文干旱联合概率分别为9.65%和8.58%,表明年尺度上流域来水对洞庭湖水文干旱的影响更大.在季节尺度上,洞庭湖-流域系统春季水文干旱联合概率最高,且两者同时发生水文干旱事件的次数最多,表明洞庭湖春季水文干旱与流域入湖补给减少有密切关系;而洞庭湖-长江系统,其秋季水文干旱联合概率最大,尤其自2003年以后更加极端和频发,这一方面受秋季降水减少和流域内人类活动的影响,另一方面三峡水库秋季蓄水使长江中下游干流水位降低,长江对湖泊顶托作用减弱也是重要原因之一.;Lake Dongting is an important river-connected lake with a complicated water system pattern in the middle reaches of the Yangtze River. Under the dual influence of climate change and human activities, the river-lake relationship has changed and extreme drought events have occurred frequently in recent years. Based on the measured data of the hydrological stations of Lake Dongting, the catchment of Lake Dongting and the tributary of the Yangtze River, this study identifies hydrological drought events through the standard water level index (SWI) and the standard runoff index (SRI). Copula function is employed to analyze the characteristics of joint probability distribution of concurrent hydrological drought in the lake-catchment-river system. The results revealed that there were 9 hydrological drought events in Lake Dongting and the probability of hydrological drought was 14.01% from 1964 to 2016. Meanwhile, the joint probability of concurrent hydrological drought in the Lake Dongting-catchment system and Lake Dongting-Yangtze River system were 9.65% and 8.58%, which indicates that the inflow from the basin has a greater impact on the hydrological drought of Lake Dongting on the annual scale. On the seasonal scale, the joint probability of hydrological drought in the spring of the Lake Dongting basin system is the highest, and the number of hydrological drought events occurring concurrently is the most, indicating that the hydrological drought in the spring of Lake Dongting is closely related to the decrease in the recharge to the basin. The Lake Dongting-Yangtze River system has the highest joint probability of hydrological drought in autumn, especially since 2003. On the one hand, it is affected by the reduction of autumn precipitation and human activities in the basin. On the other hand, it is also one of the important reasons that the autumn impoundment of the Three Gorges Reservoir reduces the water level of the middle and lower mainstream of the Yangtze River, which weakened the blocking effect of the Yangtze River.