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In the midst of global climate change, a large typhoon has hit Japan and unprecedented heavy rainfall is occurring. In large cities in Japan, underground discharge channels and underground regulating reservoirs are being developed to improve the flood control safety. In this paper, we confirm the flood reduction effect of these underground facilities against the rainfall generated by Typhoon Hagibis in the Tokyo area in 2019. In addition, the advantages of underground regulating reservoirs in the metropolitan area are discussed from two aspects: cost and land acquisition. It is confirmed that the underground reservoir type has remarkable advantages in both aspects.

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In this study, we surveyed the entrances/exits of all 216 underground stations in the wards of Tokyo, and provides a detailed analysis of the buildings with entrances of stations. Result shows that (1) in recent years, entrances have tended to be located on private land and railway sites, (2) 69.5% of entrances of stations located in buildings are in the four central wards of Tokyo, and (3) the number of "complex" pattern of connections between buildings and entrances of stations has been increasing since the 2010s. In addition, it was found that, (4) since in 1990s, the building construction projects that uses urban development systems have improved entrances facilities of stations, such as installation of elevators, common corridors and expansion of subway concourses. Keywords: buildings with entrances of underground stations, pattern of connections between buildings and entrances of stations, urban development systems 地下駅連絡建物, 地下駅出入口との連絡形式，都市開発諸制度