2019 Volume 14 Issue 1 Pages 233-245
In this study, regional characteristics of heavy rainfall （≥20 mm/h） occurrence were analyzed from the viewpoint of the spatial extent of rainfall area （≥5 mm/h） using hourly data from 290 densely distributed rain-gauge stations for 15 summers （from June to September），mainly in metropolitan Tokyo and Saitama prefecture. Our results revealed that in the eastern foothills of the Kanto Mountains and the western and northern wards of Tokyo, the localized heavy rainfall frequency was high and the associated rainfall amounts were large. Conversely, near the Kanto Mountains and in western Saitama prefecture and the Tama region of Tokyo, frequencies of heavy rainfall with widespread rainfall areas were high, associated with large amounts of rainfall. Furthermore, we examined the relationship between wind systems and heavy rainfall occurrence in eastern Saitama prefecture, located 20–50 km leeward of central Tokyo, with southerly winds. The ratio of localized heavy rainfall to total heavy rainfall frequency was high throughout the summer. We confirmed that southerly wind convergence with northerly winds from the inland areas of the Kanto Plain and convergence of southerly winds from Sagami Bay and southeasterly winds from Tokyo Bay as well as that with easterly winds （known as the E–S type） played an important role in the occurrence of localized heavy rainfall in this region.
