珠江河口区复合洪水事件多要素非一致性的时变遭遇分析

Multi-Element Non-Coherent Time-Varying Encounter Analysis of Complex Hazards Contributing to Pearl River Estuary Flooding

利用1988—2017年珠江河口三灶站潮位、澳门风速、上游流量日极值数据,基于广义可加模型(GAMLSS)的非一致性频率计算方法与时变Copula函数,对上游洪水、台风和天文潮的复合洪水事件重现期及其主控因子展开研究,结果表明:1)珠江河口区潮位、风速、流量均为非一致性序列,构建的时变Copula模型相比传统恒定参数的Copula更符合实际情况。2)1988—2017年珠江河口区典型复合洪水事件发生周期随时间不断缩短,发生概率增大,未来极端复合洪水事件发生概率增强。“黑格比”台风引发的复合洪水事件重现期从1988年的13.06 a一遇减小到2017年的10.80 a一遇,“韦森特”“天兔”引发的复合洪水事件在1988—2017年重现期缩短了1.06和0.97 a;3)当3种因子重现期为5 a一遇时,珠江河口区复合洪水事件主要受台风风速影响较大;重现期为10、20、50 a一遇时,复合洪水事件主要受天文潮潮位影响较大。

In conjunction with global warming,the frequency and intensity of typhoons in the Pearl River Estuary region are increasing annually,and coastal cities are becoming more vulnerable to compound disasters triggered by upstream flooding,typhoons,and astronomical tide surges,seriously threatening the lives and properties of people in the delta region.Quantitative analysis of the degree of variability of each factor associated with a compound flood event and accurate assessment of the magnitude of the compound flood event strongly impact the efficacy of coastal city responses aimed at disaster prevention and damage mitigation.In this study,focused on the Pearl River Estuary area,the tide levels at Sanzao station,wind speeds at Macao station,and daily maximum the maximum daily flow at Sanshui and Makou stations spanning 30 years from 1988 to 2017 were used to characterize the flood magnitude,typhoon magnitude,and astronomical tide magnitude of compound flood events in the Pearl River Estuary area.Data were screened using the annual maximum method.Based on the generalized additive model(GAMLSS)and the time-varying copula function,the encounter combinations of composite flood events of different levels and their main controlling factors were investigated.The results show that:1)the main factors influencing initiation and magnitude of composite flood events in the Pearl River estuary area are non-consistent sequences that display interdependence.The time-varying copula model constructed in this study is more suitable for studies of composite floods than the traditional constant parameter copula model.Copula models are most applicable to studies of the encountered characteristics of multiple elements contributing to compound flood events and are most in line with actual situations.2)Compared with the joint return period of traditional constant copula parameters,the period of occurrence of typical compound flood events in the Pearl River Estuary from 1988 to 2017 continuously shortens with time,the probability of occurrence increases,and the probability of future occurrence of extreme compound flood events is strengthening.The trend in which the return period of compound flood events is shortening with higher grades is accelerating.3)Compound flood events throughout the Pearl River estuary area are more affected by typhoons and astronomical tides and less affected by water flow.When the return period of the three factors is one in 5 years,water flow causes the smallest increase in the co-occurrence return period;i.e.,the influence of astronomical tide and typhoon on the scale of upstream flooding,composite flood events of typhoon,and astronomical tide is proportionately larger.Thus,composite flood events in the Pearl River estuary area are mainly impacted by typhoons with higher wind speeds.When the return period of the three factors is one in 10,20,and 50 years,the increase in the cooccurrence return period caused by flow changes the most;and when the return period of the three factors is one in 10,20,and 50 years,the acceleration of the co-occurrence return period caused by flow is the largest.When the three factors have a larger return period,astronomical tide exerts proportionately greater influence on the scale of the composite flood event of upstream flood,typhoon,and astronomical tide.