Long‐term trends in snowfall characteristics and extremes in Japan from 1961 to 2012

The region of Japan along the Japan Sea is one of the heaviest snowfall regions in the world, and it appears to be increasingly vulnerable to climate variability and global warming. This study investigated the long‐term trends in snowfall characteristics and extremes (i.e., heavy snowfall) over Japan mainly using station observations over 51 years from the 1961/1962 to 2011/2012 winter seasons. Long‐term trends were examined in terms of total precipitation and the ratio of the numbers of snowfall days to precipitation days R(s/p). Our results show statistically significant decreasing trends in seasonally accumulated snowfall at most stations in Japan, except for those in northern Tohoku and Hokkaido Districts and the Pacific side of Japan. These significant decreasing snowfall trends were associated with the long‐term decrease in R(s/p). Although long‐term decreasing trends in R(s/p) were also observed over Tohoku District and Pacific side, increasing trends in precipitation cancelled the decreasing trends there, which indicates long‐term trends in precipitation likely complicated snowfall trends. Over Hokuriku District, a decrease in precipitation enhanced the decrease in snowfall. Moreover, major snowfall events occurred in the first half of the study period, whereas a recent increase in heavy snowfall was not yet evident. The region of Japan along the Japan Sea is one of the heaviest snowfall regions in the world, and it appears to be increasingly vulnerable to climate variability and global warming. Long‐term trends were examined in terms of total precipitation and the ratio of the numbers of snowfall days to precipitation days R(s/p). Although the decreasing trends in R(s/p) due to SAT warming can explain most decreasing trends in snowfall, increasing trends in precipitation cancelled the decreasing trends, which indicates long‐term trends in precipitation likely complicated snowfall trends. Over some regions, a decrease in precipitation enhanced the decrease in snowfall. Moreover, major snowfall events occurred in the first half of the study period, whereas a recent increase in heavy snowfall was not yet evident.