Study on the characteristic features of the recent variation of mountainous heavy rainfall and discussion on the mechanism using numerical modeling

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The significant positive trend in nocturnal heavy rainfall was found over around the southeastern foot of the mountains in the northern Kanto district through the analysis of 31 years' worth of AMeDAS data. In addition, the specific humidity at 850 hPa also increased on convective days. A numerical study elucidated that the cumulonimbus clouds around the southeastern foot of the mountains became active in the night when specific humidity increased. It is suggested that recent increase in specific humidity is the cause of recent positive trend of heavy rainfall.