Rapid Intensification and Relative Sea-Level Rise Amplify Compound Flooding

Rapid intensification (RI) of hurricanes and relative sea-level rise (RSLR, the combined effect of 15 global sea-level rise and regional land subsidence) exacerbate compound flood risks by 16 increasing the likelihood of coinciding surge and rainfall extremes. However, their combined 17 influence on flooding remains insufficiently understood. This study examines how RI and RSLR 18 jointly affect compound flooding using hurricanes Harvey (2017) and Beryl (2024) along the 19 Texas Gulf Coast. A reduced-complexity model efficiently simulates flood dynamics from rainfall, 20 river discharge, and coastal storm surge across diverse coastal settings. Flood attribution metrics 21 reveal distinct mechanisms: Harvey’s prolonged rainfall-driven intensification produced 22 widespread inland flooding with strong rainfall-flood correlation (r > 0.7) and amplification, 23 quantified using the compound index difference (CI_diff > 0.5 m over 75% of Zone 2). In 24 contrast, Beryl’s wind-driven intensification caused surge-dominated flooding with limited 25 inland compounding. Spatiotemporal analysis confirms that the structure and timing of RI 26 phases critically shape the extent and dominance of flood drivers. A synthetic re-simulation of 27 Harvey under 2024 sea-level conditions demonstrates that modest RSLR (~3–6 cm, 2017–2024) 28 increased flood depths (2–5 cm) and expanded flood extent (~1.5%), particularly in low-lying 29 estuarine areas. While the overall response appears quasi-linear, localized nonlinear 30 amplification emerges due to topographic thresholds and interacting drivers. These effects were 31 intensified by antecedent hydrologic conditions such as saturated soil and elevated river stages. 32 Our findings emphasize the importance of integrated flood modeling frameworks that account 33 for near-term sea-level trends and storm evolution characteristics to inform climate-resilient 34 flood mitigation and adaptation strategies.