Joint series underlying the paper " Compound coastal-riverine flooding of St. Lawrence River coasts under sea level rise conditions"

Compound coastal-riverine flooding, known as flooding events caused by the co-occurrence of high streamflow and coast water levels, can have substantial economic and social implications in low-lying coastal regions. Recent studies over Canada’s coasts have shown that neglecting the interdependency between flood drivers can underestimate the risk of flooding by up to 50%. However, to date, such interdependency and its effect on the frequency of compound riverine-coastal flooding has not been investigated for the coasts of the St. Lawrence River, Estuary, and Gulf system (StL), where Sea Level Rise (SLR), along with intensified river peaks, are already threatening communities. In this study, a copula-based bivariate frequency analysis (AND hazard scenario) was applied to quantify the differences between joint return periods computed under dependent and independent assumptions, for 26 sites along the StL. Furthermore, design pairs for 100-year joint events in the historical period (1986-2020) were compared with the 2100 horizon, where the SLR associated with the RCP8.5 emission scenario was incorporated into the water level time series. Results show that 1) the independence assumption can underestimate the frequency of compound flooding in the Fluvial Section of the StL by up to 30 times and 2) the SLR can increase the frequency of compound flooding by up to 50 times in the Estuary and the Gulf and by up to 5 times in the Fluvial Section of the StL. This study highlights the need for explicit consideration of the dependence between flood drivers and of SLR in the delineation of flood maps along all of the coasts of the St. Lawrence.复合滨海-河流洪水（Compound coastal-riverine flooding）指由高径流与海岸水位同时升高引发的洪水事件，在低洼沿海地区可能造成严重的经济与社会影响。此前针对加拿大沿海地区的相关研究表明，若忽略洪水驱动因子间的相互依赖关系，洪水风险的评估结果最高可被低估50%。然而截至目前，针对圣劳伦斯河、河口及海湾系统（StL）沿岸区域，尚未有研究探讨此类驱动因子间的依赖关系及其对复合滨海-河流洪水发生频率的影响；而该区域的海平面上升（Sea Level Rise，SLR）与加剧的河流洪峰已对沿岸社区构成威胁。本研究针对StL沿岸的26个站点，采用基于Copula函数的双变量频率分析（联合灾害情景，AND hazard scenario），量化了在依赖与独立两种假设下计算得到的联合重现期之间的差异。此外，本研究将历史时段（1986-2020年）内百年一遇联合事件的设计水情组合，与2100年预测情景进行对比；该2100年情景中将关联典型浓度路径8.5（Representative Concentration Pathway 8.5，RCP8.5）排放情景的海平面上升效应纳入水位时间序列之中。研究结果表明：1）在圣劳伦斯河河流段，采用独立假设会使复合洪水发生频率的评估结果最高被低估30倍；2）在河口与海湾区域，海平面上升可使复合洪水发生频率最高提升50倍，而在圣劳伦斯河河流段，该提升幅度最高可达5倍。本研究强调，在圣劳伦斯河全沿岸区域的洪水图绘制工作中，需明确考量洪水驱动因子间的依赖关系以及海平面上升的影响。