Portions of East Asia often experienced extremely heavy rainfall events over the last decade. Intense atmospheric rivers (ARs), eddy transports of moisture over the middle latitudes, contributed significantly to these events. Although previous studies pointed out that landfalling ARs will become more frequent under global warming, the extent to which ARs produce extreme rainfall over East Asia in a warmer climate remains unclear. Here we evaluate changes in the frequency and intensity of AR‐related extreme heavy rainfall under global warming using a set of high‐resolution global and regional atmospheric simulations. We find that both the AR‐related water vapor transport and rainfall intensify over the southern and western slopes of mountains over East Asia in a warmer climate. ARs are responsible for a large fraction of the increase in the occurrence of extreme rainfall in boreal spring and summer. ARs will bring unprecedented extreme rainfall over East Asia under global warming.

To investigate future changes in snow cover and snowfall over mountainous areas in central Japan, we conducted regional climate projections using a high-resolution non-hydrostatic regional climate model (NHRCM) with 5 km and 1 km grid spacings. Boundary conditions are derived from the database for Policy Decision making for Future climate change (d4PDF) 20 km regional climate projections (d4PDF20). The d4PDF20 assumes two future climates when global mean surface air temperatures are approximately 2 K and 4 K warmer than in the preindustrial period. Experiments with 5 km grid spacing are conducted by NHRCM for 372 years in d4PDF20 in each climate. Experiments with 1 km grid spacing are performed focusing on 5 years with heavy, median, and light snow cover of mountainous areas in each climate. In the years with heavy snow cover in 2 K and 4 K warming climates, snowfall is enhanced from late December to February at more than 2000 m above sea level (mASL) in the northern parts of Japan’s Northern Alps, resulting in heavy snow cover comparable to that in the present climate. Heavy daily snowfall remarkably increases due to global warming in the years with heavy snow cover. At low elevations below 500 mASL, snowfall decreases in all ranges of snowfall intensity in the 4 K warming climate, while the frequency of heavy daily snowfall increases in the 2 K warming climate. Precipitation is enhanced around the Japan-Sea Polar-airmass Convergence Zone and the mountainous area facing the Sea of Japan, resulting in strengthened heavy snowfall at high elevations where the winter mean temperature is approximately − 10 °C in the present climate. On the other hand, remarkable reductions in snow cover and snowfall are projected in years with light snow cover. Our results indicate that global warming causes heavy and light mid-winter snowfalls at high elevations of Japan’s Northern Alps that are more extreme than those in the present climate. Graphical abstract