Characteristics, causes and impacts of the changes of the flood frequency in the Pearl River drainage basin from 1951 to 2010

Abstract

气候变化和人类活动导致珠江流域水文变化,变化前后洪水频率分布显著不同.运用滑动秩和(Mann-Whitney U test)结合Brown-Forsythe、滑动T、有序聚类和Mann-Kendall检验法,并用累积距平曲线法获取年最大流量序列详细信息,综合确定样本最佳变化节点,并对水文变化成因做了系统分析.在此基础上,对整体序列、变化前后序列用线性矩法推求广义极值分布参数以及不同重现期设计流量.结果表明:(1)西江大部以及北江流域最佳变化节点在1991年左右;东江流域最佳变化节点与该流域内3大控制性水库建成时间基本吻合;(2)变化后,西江、北江年最大流量持续增加,洪峰强度增大,尤其是西江干流年最大流量显著增加;东江流域年最大流量显著减小,洪峰强度降低;(3)变化后,西江与北江洪水风险增加,尤其是下游珠三角地区本身受人类活动显著影响,加之西江与北江持续增加的洪水强度,珠三角地区发生洪水的强度及频次加剧,而东江洪水风险减小.此研究对于珠江流域在变化环境下的洪水风险评估与防洪抗灾具有重要意义.;Climate changes and human activities have led to significant variations in the hydrological conditions in Pearl River drainage basin. Distributions of flood frequencies before and after the hydrological change are significantly different. We used moving rank sum test (Mann-Whitney U test) and Brown-Forsythe, Sliding T, Ordered Cluster, and Mann-Kendall (MK), with cumulative departure curve method (CSDMC) for annual maximum discharge (AMD) details, to analysis hydrological changes and their causes. Then, L-moment was used to evaluate the parameters of generalized extreme value distributions of the whole, before and after the hydrological changes of annual maximum discharge series. The design flow values of different return periods were calculated. Results show that:(1) Hydrological changes at the stations in Beijiang River and most of Xijiang River occurred in 1991, and hydrological regulation of the three big reservoirs was the main factor in Dongjiang River. (2) After hydrological change, annual maximum discharge and flow peak intensity were increased in Xijiang River and Beijiang River, especially in the main stream of Xijiang River while opposite situation occurred in Dongjiang River. (3) After hydrological change, flood risk had been increased in Xijiang River and Beijiang River. In particular, because the Pearl River Delta region itself has been strongly affected by human activities, persistently increased flood intensity had occurred in the Xijiang River and Beijiang River. The Pearl River Delta floods and flood frequency had been increased significantly, while flood risk had been decreased in Dongjiang River. This study is very important for assessing the flood risks and flood disasters in the Pearl River drainage basin.