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

Abstract

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 Polarairmass 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 midwinter snowfalls at high elevations of Japan's Northern Alps that are more extreme than those in the present climate.

Regional Characteristics of Future Changes in Snowfall in Japan under RCP2.6 and RCP8.5 Scenarios

“…In Hokkaido, winter precipitation significantly increases under both RCP2.6 and RCP8.5. Under RCP8.5, changes in winter precipitation show a clear contrast between the PO and SoJ sides, which is consistent with the findings of previous studies (e.g., Kawase et al , 2016Nosaka et al 2020). The influence of changes in winter precipitation on snowfall will be discussed in Section 4.…”

“…The annual snowfall is enhanced at higher elevations over the Colorado Headwaters of the Rocky Mountains in the future climate (Rasmussen et al 2011;. Kawase et al, Regional characteristics of future snowfall changes in Japan 4 Even in Japan, mid-winter snowfall can increase over the high mountains above 2,000 m in central Japan in heavy snowfall years (Kawase et al 2020).…”

“…Some global climate models project weakened East Asian winter monsoons due to global warming (Hu et al 2000;Kimoto et al 2005;Hori and Ueda 2006), which will cause a decrease in winter precipitation along the SoJ and cause an increase in winter precipitation in Japan along the Pacific Ocean (hereafter referred to as the PO) because of the northward shift of extratropical cyclones passing south of Japan Nosaka et al 2020). The extratropical cyclones also bring heavy snowfall and rainfall over the inland areas of central Japan (Ando and Ueno 2015).…”

d4PDF: large-ensemble and high-resolution climate simulations for global warming risk assessment

“…Therefore, an optimum resolution that guarantees reliability of the outputs is not so high. For users who desire high-resolution information, dynamical downscaling to higher resolution is one of the solutions (Hoshino et al 2020;Kawase et al 2018;Kawase et al 2020;Sasai et al 2019). Meanwhile, the models used in d4PDF are the same as those used operationally at JMA.…”

Snow water scarcity induced by record-breaking warm winter in 2020 in Japan

“…Prior to the recent period of low SWE in Japan, a significant reduction due to global warming was already projected 3 , 4 . Especially, remarkable reduction in snow cover and snowfall are projected in years with light snow cover 5 . It would be informative to investigate the low SWE period in Japan in 2020, characterised by low SWE with remarkably high temperatures, as it represents a case under conditions of global warming, something that previous studies have tried to project.…”