Multi-dimensional analysis of wetness-dryness encountering of streamflow based on the Copula function in Lake Poyang Basin

Abstract

鄱阳湖流域5大水系来水变化与湖区水文极值事件有密切关系，研究径流变化特征与丰枯遭遇规律对区域防洪抗旱有重要意义.本文运用Copula函数构建了鄱阳湖水系多维径流联合分布模型，采用特枯、偏枯、平水、偏丰和特丰的径流丰枯分类，定量研究了鄱阳湖5大水系丰枯遭遇的问题，探讨了多维丰枯遭遇同步联合概率的变化特征.结果表明：鄱阳湖水系河流之间的径流具有较高的相关性，Gaussian Copula函数能较好地模拟二维至五维的径流联合分布.多条河流的丰枯遭遇随着维数的增加，丰枯组合增加，丰枯同步的联合概率明显下降，且丰枯同步的最大联合概率趋向于丰枯两端.对于相同的概率区间，非汛期径流的丰枯同步联合概率明显大于年径流和汛期径流，而年径流和汛期径流之间的丰枯同步联合概率差别较小.同处于流域北部或南部或相邻的河流之间的组合，其同步联合概率相较其他组合大，而南、北河流组合的同步联合概率相对较小.该研究可为流域水资源管理及水旱灾害预防提供科学依据.;According to previous research, there was a close relationship between the change of streamflow and the hydrological extreme events in Lake Poyang Basin. Based on the Copula function, the multi-dimensional joint distributions of streamflow in Lake Poyang Basin was built. Streamflow was classified into extra dryness, ordinary dryness, normal water, ordinary wetness and extra wetness, the problem of wetness-dryness encountering of streamflow was discussed quantitatively. Multi-dimensional joint frequencies of identical probability interval of streamflow were analysed. Results showed that there were high dependences between two rivers of Lake Poyang Basin. The Gaussian Copula fitted well the joint distributions of streamflow from two-dimension to five-dimension. As the dimension of joint frequency of multi-streamflow increased, the number of combination of wetness and dryness encountering increased, yet the joint frequency of identical probability interval decreased significantly, and then the maximum joint frequency of identical probability intervals tended to occur in the upper or down interval of the distribution of streamflow. The joint frequencies of identical probability interval of streamflow in dry period were greater than those of annual streamflow and streamflow in flood period, and those between annual streamflow and streamflow in flood were slightly different. The joint frequencies of identical probability interval of streamflow between northern rivers, southern rivers, or adjacent rivers were generally greater than those between northern and southern rivers. This study provides scientific basis for river basin resources management and drought event prevention.