Characteristics of an Extreme Rainfall Event in Kyushu District, Southwestern Japan in Early July 2020

Abstract

An extreme rainfall event brought precipitation amounts exceeding 1000 mm in Kyushu district, southwestern Japan, in early July 2020. Especially, an elongated and stagnated mesoscale convective system formed around the Kuma River in central Kyushu district produced localized heavy rainfall with precipitation amounts larger than 600 mm in 13 hours. Characteristics of this extreme rainfall event were investigated using distributions of radar/raingauge-analyzed precipitation amounts (RAP) and statistically compared with those during the warm seasons (April–November) in 2009-2019. The results are shown as follows; (1) nine heavy rainfall areas of linear-stationary type (LS-HRAs) were extracted, (2) spatial and temporal scales of two LS-HRAs among them respectively exceeded 270 km and 10 hours, (3) the maximum RAP exceeding 100 mm in LS-HRAs were comparable to those in previous extreme rainfall events, (4) large accumulated three-hour precipitation amounts exceeding 200 mm were more frequently observed than those in the previous events, and (5) the accumulated five-day precipitation amount integrated around Kyushu Island was the largest since 2009. This study also showed that the large area-integrated precipitation amount was produced mainly from widespread precipitation systems associated with the Baiu front, while the nine LS-HRAs significantly contributed localized heavy rainfall.