Abstract
Intensification of heavy precipitation foreseen in climate change studies has become a public concern, but it has not yet been examined well with observed data, particularly with data at short temporal scale like hourly data. On hourly heavy precipitation at Tokyo, previous studies investigated the data only from the 1970's due to the availability of digital data. In this research, we digitalized hourly precipitation since 1890 recorded at the Tokyo observatory in order to investigate historical changes in hourly heavy precipitation at Tokyo. The recent decade, the 1990's, was indeed a period with considerably strong and frequent hourly heavy precipitation, but another period with strong/frequent hourly heavy precipitation was found around the 1940's. Hourly heavy precipitation around the 1940's was even stronger/more frequent than in the 1990's. Thereby, it cannot be said that recent hourly heavy precipitation has become unprecedentedly strong or frequent. In addition, the numbers of hourly heavy precipitation events by tropical cyclone and by Baiu front were counted respectively, resulting in that the composition of the causes of hourly heavy precipitation events in the 1940's appears to be different from that in the 1990's.
