Atmospheric driving mechanisms of extreme precipitation events in July of 2017 and 2018 in western Japan

Abstract

The occurrence of extreme precipitation events is now a serious concern in recent years in Japan. This study explores the atmospheric driving mechanisms of two extreme precipitation events occurred during 5–6 July 2017 and 5–8 July 2018 over western Japan. We identified that the atmospheric transport of large amounts of moisture and wind streams with wind speed of minimum 15 m s⁻¹ from south of Japan towards north on the days before these torrential precipitation events are mainly responsible for the July 2017 and July 2018 floods over western Japan. However, the contributions from the moisture advections (both vertical and horizontal) to the atmospheric water budget plays key roles to intensify the precipitations during the said torrential events. We also find that the prominent moisture flux convergence and well-developed moist conditions mainly maintain these heavy precipitation events over the downpour affected area. Our overall analysis suggests that the atmospheric factors driving to all these two heavy precipitation events are qualitatively robust and vital to explain the mechanism of extreme precipitations.