Compound flood raised from the concurrent heavy precipitation and storm surge receives increasing attention because of its potential threat to coastal areas. Analyzing the past changes in the characteristics of compound flood events is critical to understand the changing flood risks associated with the combination of multiple drivers/hazards. Here, we examined the evolution of the compound flood days (defined as days of concurrent extreme precipitation and extreme storm surge exceeding the 90th percentiles) based on the observed precipitation and storm surge data across the globe. Results showed that the annual number of compound flood days increased significantly by 1–4 per decade (α=0.1) on the east coast of the US and northern Europe, while the annual number of compound flood days decreased significantly in southern Europe and Japan. The increasing trends in precipitation under extreme storm surge and storm surge under extreme precipitation were found extensively across the world except in Japan, suggesting that more intense precipitation appeared when extreme storm surges occurred, and higher storm surge emerged when extreme precipitation occurred. Comparatively, the global fractional contributions of storm surge (i.e., 65%) on changes in compound flood days were higher than that of precipitation (i.e., 35%), demonstrating that storm surge was more likely to dominate the changes in the number of compound flood days. This study presented the spatial and temporal characteristics of the compound flood events at the global scale, which helps better understanding the compound floods and provides scientific references for flood risk management and an indispensable foundation for further studies.

中文翻译：

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全球范围内同时发生的强降水和风暴潮的频率和强度的演变：对复合洪水的影响

同时发生的强降水和风暴潮引发的复合洪水因其对沿海地区的潜在威胁而受到越来越多的关注。分析复合洪水事件特征的过去变化对于了解与多种驱动因素/灾害组合相关的不断变化的洪水风险至关重要。在这里，我们根据观测到的全球降水和风暴潮数据，研究了复合洪水天数（定义为极端降水和极端风暴潮同时发生的天数超过 90%）的演变。结果表明，美国东海岸和北欧的年复合洪水日数每十年显着增加1-4天（α=0.1），而南欧和日本的年复合洪水日数显着减少。除日本外，极端风暴潮和极端降水风暴潮的降水增加趋势在世界范围内广泛存在，表明极端风暴潮发生时降水更强烈，极端降水发生时风暴潮升高。相比之下，风暴潮对复合洪水天数变化的全球部分贡献（即 65%）高于降水（即 35%），表明风暴潮更有可能主导复合洪水天数的变化。洪水天。本研究展示了全球范围内复合洪水事件的时空特征，