Journal Article

Quantitative Stress Test of Compound Coastal‐Fluvial Floods in China's Pearl River Delta

Wang, Xiaola, Qiu, Jiangchao, Yang, Fang, He, Xiaogang, Liu, Bingjun

2022

Overview

Floods in river deltas are driven by complex interactions between astronomical tides, sea levels, storm surges, wind waves, rainfall‐runoff, and river discharge. Given the anticipated increase in compound flood hazards in river deltas in a warming climate, climate‐informed regional to local extreme water levels (EWLs) is thus critical for decision‐makers to evaluate flood hazards and take adaptation measures. We develop a simple yet computationally efficient stress test framework, which combines historical and projected climatological information and a state‐of‐the‐art hydrodynamic model, to assess future compound coastal‐fluvial flood hazards in river deltas. Our framework is applied in the world's largest single urban area, China's Pearl River Delta (PRD), which is also characterized by densely crossed river network. We find that extreme sea level is the dominant driver causing the compound coastal‐fluvial flood in the PRD over the past 60 years. Meanwhile, there is large spatial heterogeneity of the individual and compound effects of the typhoon intensity, local sea‐level rise, and riverine inflow on coastal‐fluvial floods. In a plausible disruptive scenario (e.g., a 0.50 m sea‐level rise combined with a 9% increase in typhoon intensity in a 2°C warming), the EWL will increase by 0.76 m on average. An additional 1.54 and 0.56 m increase in EWL will occur in the river network and near the river mouth, respectively, if coastal floods coincide with the upstream mean annual flood. Findings from our modeling framework provide important insights to guide adaptation planning in river deltas to withstand future compound floods under climate change. Plain Language Summary Compound floods pose serious threats to the dense population living in river deltas worldwide. Climate change could increase the compound flood hazards through stronger tropical cyclones, sea level rise, higher extreme precipitation, and river flows. It is urgent to understand how the so‐called grey swan events will evolve under a changing climate in these already flood‐prone areas. Here, grey swan events are high‐consequence events that are beyond people's experience but may be foreseeable and thus can be systematically prepared for. In this study, a storyline‐based framework is proposed to assess the potential grey swan compound floods under a warming climate. We apply this framework to China's Pearl River Delta, the world's largest single urban area. In a plausible disruptive scenario (e.g., a 0.50 m sea‐level rise combined with a 9% increase in typhoon intensity in a 2°C warming), we find that extreme water levels will increase by 0.76 m on average. Our flexible and computationally efficient storyline‐based framework could guide coastal planners to prepare for the grey swan compound flood hazards under climate change. Key Points A quantitative stress test framework is proposed to assess the compound coastal‐fluvial flood in the river delta at minimal cost A state‐of‐the‐art unstructured mesh generation technology is applied to develop an objective and reproducible hydrodynamic model Compound effects of typhoon intensity, local sea‐level rise, and river inflow on coastal‐fluvial floods are systematically investigated

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Adaptation / China / Climate change / Climatic changes / Coastal flooding / Deltas / Disaster planning / Emergency management / Environmental aspects / Flood hazards / Floods / Geomorphology / Global warming / Hazard assessment / Heterogeneity / hydrodynamic model / Hydrodynamic models / Influence / Local climates / Methods / Rain / Rainfall / Regional climates / Reproducibility / River discharge / River flow / River mouth / River networks / Rivers / Runoff / Sea level / sea level rise / Simulation / Spatial heterogeneity / Storm surges / Stream flow / stress test / tidal river delta / Tidal waves / typhoon intensity increase / Typhoons / Urban areas / Water inflow / Water levels / Wind / Wind waves