Changes in extremely heavy and light snow-cover winters due to global warming over high mountainous areas in central Japan

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.