In recent years, heavy rainfall has been occurring not only in the Kyushu regionbut also in the Tohoku and Hokuriku regions during the warm season in Japan. Heavy rainfall requires the right conditions. Among them, it is necessary that water vapor be supplied to the atmosphere and that be properly transported to the appropriate precipitation regions. The relationship between water vapor transport and heavy rainfall has been widely conducted. However, relatively few papers have been based on the identification of water vapor sources and water vapor balance analysis in heavy rainfall. In this study, I estimate the water vapor source of the heavy rainfall that occurred in the Tohoku and Hokuriku regions in August 2022 using backward trajectory analysis. The purpose is to clarify how air masses were transported to the Tohoku and Hokuriku regions and how water vapor was accumulated. So, this study conducted a reproduction experiment of the events using Cloud Resolving Storn Simulator(CReSS) and identified air parcels flowing into the Tohoku and Hokuriku regions using backward trajectory analysis and, the water vapor budget was examined on the path of air parcels flowing in the lower layers to estimate the water vapor sources in heavy rainfalls. From August 2 to 4, the air parcels flowing into the Tohoku and Hokuriku regions is dry in the middle layer and moist in the lower layer, indicating that the atmosphere is unstable. And, the water vapor balance in the air parcels flowing in the lower layers (below 1000 m altitude) in the Tohoku and Hokuriku regions indicates that the water vapor supply from the Japan Sea is extremely small. The water vapor balance of the air parcels on the upwind side was investigated, and it was shown that water vapor is supplied from the sea area near or south of Okinawa. The relative humidity of the air parcels located near Okinawa was high. This suggests that water vapor from further upwind regions is important.