Author(s): Koji Asai; Koji Nishiyama; Hajime Shirozu

Linked Author(s): Koji Nishiyama, Hajime Shirozu

Keywords: SOM; Meteorological filed; Heavy rainfall; Pattern analysis

Abstract: Japan is one of the countries that are suffering from rainfall disasters. Mainly, heavy rain disasters are induced by Baiu front and typhoons. Recently, heavy rain disasters caused by Baiu front have frequently occurred. It is needed to store the findings relating to heavy rainfall mechanisms, and it is desirable to make use of those findings to heavy rainfall. There are so many research or studies for heavy rain disasters. However, those studies almost related to each disaster. We can understand the heavy rain mechanism for each disaster from those studies, but it is not well known how meteorological patterns relate to the heavy rainfall disasters if only one disaster is focused. Therefore, it would be useful that the metrological filed patterns which induce the sever disasters are classified. This study investigated relationships between meteorological field patterns and heavy rainfall in western Chugoku and northern Kyushu in Japan using Self Organizing Map (SOM). The reanalyzed meteorological field data by NCEP from 1979 to 2019 in northern Kyushu and Chugoku districts were in order to create SOM. This study investigated features of meteorological fields relating to the heavy rainfall case on July 2018 causing the historical serious debris flow disaster in Hiroshima prefecture. The past heavy rainfall cases in Hiroshima prefecture showed strong convective activity characterized commonly by low level jet and high precipitable water. The most serious disaster case in 2018 was classified into dangerous meteorological field patterns leading to heavy rainfall. The meteorological field patterns of the event were similar to that of the heavy rainfall event occurring on July 24, 2009. The common features between both cases showed the formation of widespread heavy rainfall area, and the occurrence of serious disaster both in Fukuoka and Hiroshima prefecture. Similarly, we also investigated the other heavy rainfall disasters. We found the meteorological field classification with SOM is very useful to make a comparison between the meteorological filed we focused now and the past similar meteorological filed.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022405

Year: 2022