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© 2019 American Meteorological Society For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy. Extremely heavy precipitation occurred from central to western Japan in July 2018, which was named the “heavy rain event of July 2018” by the Japan Meteorological Agency (JMA). The JMA has approximately 1,300 in situ stations. The 48and 72-h total precipitation records were broken at 125 and 123 in situ stations, respectively, from 28 June to 8 July (the dates are different in the individual in situ stations). The 10-day total precipitation accumulated at all Japanese in situ stations was the highest for any 10-day periods starting on the 1st, 11th, and 21st of the month since 1982 (Fig. 1a) (Shimpo et al. 2019; TCC JMA 2018). During the heavy rainfall event, there were 221 fatalities, and more than 6,000 buildings were destroyed by floods and landslides (Cabinet Office, Government of Japan 2018). The continuous lower-level moisture transport maintained the active stationary weather front for a couple of days and the passage of the upper-level trough enhanced the heavy precipitation at the end of this heavy rainfall event (Shimpo et al. 2019; TCC JMA 2018). Mesoscale lineshaped precipitation systems appeared locally and strengthened the heavy precipitation in some areas of western Japan (Tsuguti et al. 2019). In recent years, the surface air temperature during the summer has been increasing rapidly in Japan. The moisture that the atmosphere may hold has increased by approximately 7% K−1 as dictated by the Clausius– Clapeyron relationship. The observed specific humidity at 850 hPa in July shows a rapid increase around Japan from 1981 to 2018 (Shimpo et al. 2019; TCC JMA 2018). It is possible that recent warming and moistening due to global warming contributed to the heavy rain event of July 2018. Event attribution (EA) is useful for the attribution of specific extreme events, such as heat waves and drought, to global warming due to anthropogenic forcing (e.g., Stott et al. 2004; Shiogama et al. 2013, 2014; Imada et al. 2014). EA uses large ensemble historical and non-warming simulations performed by general circulation models (GCMs) and probabilistically attributed the extreme event to global warming. For the latest extreme event in Japan, Imada et al. (2019) revealed that the July 2018 heat wave event in Japan would have been virtually impossible without anthropogenic global warming. Kim et al. (2019) revealed that the combination of extreme events in Japan, such as the serious flood and heatwave events that occurred in 2018, could be heavily influenced by global warming, even though the intermodel variability is large. However, it is difficult to adapt the EA to heavy precipitation events. Imada et al. (2013) attributed the heavy precipitation event occurring in southwestern Japan in 2012 to global warming using the atmospheric GCM (AGCM) with approximately 150-km horizontal resolution, while they could not simulate the local-scale heavy precipitation. Higherresolution simulations, such as 5-km grid spacings, are needed to directly reproduce such heavy precipitation influenced by the complex orography in Japan. The storyline approach (Shepherd et al. 2018) is the other approach to evaluating the impact of global warming on extreme events. In the storyline THE HEAVY RAIN EVENT OF JULY 2018 IN JAPAN ENHANCED BY HISTORICAL WARMING

The Heavy Rain Event of July 2018 in Japan Enhanced by Historical Warming