Enhancement of heavy daily snowfall in central Japan due to global warming as projected by large ensemble of regional climate simulations

This study investigates future changes in the accumulated and daily heavy winter snowfall in central Japan and the surrounding regions. We analyze outputs of the 48-member ensemble regional climate simulations in the historical and future climates. In the historical climate simulations, each ensemble member has a 61-year simulation from September 1950 to August 2011. For the future climate simulations, we also conduct 61-year simulations assuming the climate at the end of the twenty-first century (2080–2099) when the global mean surface air temperature is about 4 °C warmer than the pre-industrial climate (1861–1880) as projected under the Representative Concentration Pathway (RCP) 8.5 scenario. Our simulations show that the heavy snowfall occurring at a frequency of every 10 years is enhanced in the inland areas of the central part of the Japanese archipelago (central Japan) where the total winter snowfall amount decreases significantly. Heavy snowfall is also intensified in the northern part of the Asian continent where the surface air temperature is much colder than over central Japan. A composite analysis of heavy snowfall events in central Japan indicates that such events occur when the Japan Sea polar air mass convergence zone (JPCZ) appears during the East Asian winter monsoon season. In the future climate projections, the JPCZ is intensified since the warm ocean supplies more moisture due to warming. An upward wind anomaly is also found over the windward side of mountains where the upward flow is prevalent climatologically. The intensification of both the JPCZ and the upward wind over the mountain ranges result in the enhancement of heavy snowfall in inland areas where the surface air temperature is still below 0 °C.