Review on flood and waterlogging disasters in underground metros in large cities of China

In recent years, climate change has led to an increased frequency of urban floods, which not only damage surface buildings but also submerge underground spaces. This review study compiled global flood cases in underground spaces from 2010 to 2024. Based on the analysis of statistical flood cases, the disaster mechanism of floods in underground spaces was explored. Moreover, risk analysis approaches for floods in underground spaces were summarized into three types: multi-criteria decision making (MCDM)-based quantitative evaluation, scenario-based qualitative prediction, and machine learning (ML)-based techniques. The advantages and disadvantages of these methods were discussed. Two typical subway flood incidents in Hong Kong, China and Zhengzhou, China were analyzed to provide further implications for flood mitigation in underground spaces. To effectively prevent floods, entrances and exits of underground spaces should be positioned at elevated locations and comply with established flood prevention standards. This review study puts forward new perspectives on strategies for flood mitigation in underground spaces, emphasizing the importance of data collection, risk assessment, and the establishment of early warning systems. It is hoped that this review will be helpful for flood mitigation in underground spaces and the safe operation of underground infrastructures.