Analysis of compound floods from storm surge and extreme precipitation in China

To enhance flood protection and risk reduction in China's coastal cities, it is crucial to comprehend the variability and underlying causes of compound floods along the coasts arising from storm surges and intense precipitation. The variability of compound floods from storm surge and extreme precipitation from 1958 to 2014 was analyzed using daily maximum sea level data and daily cumulative precipitation from 16 tide gauges along the coast of China. More than 70 % of the storm surges that caused damage from 1989 to 2014 at 14 out of 16 tide gauges were compound floods. We found a strong and seasonally varying dependence between storm surges and extreme precipitation along the coast of China. There were generally positive trends for the annual number of compound events at tide gauges south of 35°N. Compound flood variability was related to large-scale climate modes. The Arctic Oscillation in March was significantly negatively correlated with the compound events at tide gauges north of 35°N, while the opposite was true at tide gauges south of 35°N. The compound events were significantly correlated with the Pacific Decadal Oscillation (PDO) in June at 10 of the 16 tide gauges, and negatively correlated with the Niño1 + 2 index in February at 7 of the 16 tide gauges. Precipitation extremes determine the changes in the occurrence of compound floods, and by modifying the East Asian summer monsoon and typhoons, the large climate modes are supposed to impact the occurrence of compound floods. Our findings can enhance our understanding of compound floods and provide an important reference for flood risk management, particularly for low-lying coastal cities in China.