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

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 degrees 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.