Increasing urban flooding facing metro system: Evidence from Internet media records in China from 2001 to 2021

Metro systems, as a vital type of underground transportation infrastructure, are particularly vulnerable to urban flooding in the changing climate. However, current understanding of the characteristics of flood-prone subway stations, including their spatiotemporal distribution and determinants is limited. This study, via Internet media big data mining, extracted 327 subway station flooding events in 33 cities of China from 2001 to 2021, and identified the relationship between the subway flooding occurrences and meteorological, topographical, and underlying surface factors. We found that annual subway station floodings and cities experiencing such events significantly increased in China. Among these events, flooding inside subway stations, flooding at subway station entrances and subway station ceiling leaks accounted for 24.77 %, 60.86 %, and 14.37 %, respectively. Twenty-four-hour precipitation of>25 mm, in combination with a slope of 5∼15°, relative DEM<48 %, watershed area of 97.46–179.42 km², impervious surface ratio>80 %, no green or blue space, and age of subway station<5 years is most frequently associated with these subway flooding events. In particular, underlying surface characteristics are the most vital factors, highlighting the importance of climate-resilient urban land use planning.