An unprecedentedly large ensemble of climate simulations with a 60-km atmospheric general circulation model and dynamical downscaling with a 20-km regional climate model has been performed to obtain probabilistic future projections of low-frequency local-scale events. The climate of the latter half of the twentieth century, the climate 4 K warmer than the preindustrial climate, and the climate of the latter half of the twentieth century without historical trends associated with the anthropogenic effect are each simulated for more than 5,000 years. From large ensemble simulations, probabilistic future changes in extreme events are available directly without using any statistical models. The atmospheric models are highly skillful in representing localized extreme events, such as heavy precipitation and tropical cyclones. Moreover, mean climate changes in the models are consistent with those in phase 5 of the Coupled Model Intercomparison Project (CMIP5) ensembles. Therefore, the results enable the assessment of probabilistic change in localized severe events that have large uncertainty from internal variability. The simulation outputs are open to the public as a database called “Database for Policy Decision Making for Future Climate Change” (d4PDF), which is intended to be utilized for impact assessment studies and adaptation planning for global warming.

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Large ensemble pairs of high‐resolution global and regional climate simulations, which are composed of 100 members of 60 years each, make it possible to attribute changes in local‐scale heavy precipitation to historical global warming. Mountain ranges separate local climates and can modulate the impact of global warming on heavy precipitation. In the summer, Japan's Kyushu region, with mountain ranges approximately 200‐km long from south to north, receives large amounts of precipitation. Over western Kyushu, the monthly maximum daily precipitation (maxPrdaily) in July increases due to historical global warming, while the maxPrdaily is unchanged over eastern Kyushu. Moisture advection and convergence due to stationary weather fronts are primary factors causing heavy precipitation in western Kyushu and moistening due to warming increases the maxPrdaily. On the other hand, typhoons heading to Kyushu are related to heavy precipitation over eastern Kyushu. The changes in typhoons heading to Kyushu result in unchanged maxPrdaily in eastern Kyushu. Our results suggest that local‐scale mountain ranges can change synoptic‐scale disturbances causing heavy precipitation and modulate the impact of historical global warming on heavy precipitation across mountain ranges.

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experiments are applied to the lateral boundary conditions of the regional climate model. 35Dynamical downscaling using d4PDF (d4PDF-DS) enables us to evaluate much heavier 36 snowfall events than those simulated by dynamical downscaling using JRA-55 (JRA55-DS). 37Over the Sea of Japan side, heavy snowfall occurs due to cold air outbreaks, while