Meteorological and snow conditions in the mountainous areas of Japan

The two largest islands of Japan, Honshu and Hokkaido, are located on the east side of the Eurasian Continent and heavy snowfall happens when the strong winter monsoon wind blows over the Sea of Japan. Especially, in mountainous areas of Honshu Island, maximum snow depth exceeds 6 m with its water equivalent as more than 3000 mm. Melt water from snow pack is a very important water resource and it is very important to determine the mass of snow cover in Japanese mountainous areas, but there were few continuously operating meteorological stations in Japanese mountain areas due to severe winter conditions.

National Research Institute for Earth Science and Disaster Prevention (NIED) constructed a Snow and Weather observation Netwok (SW-Net) in Japanese mountainous areas and has been monitoring the meteorological and snow conditions for more than 10 years including a heavy snow fall winter (2005/2006) and an anomalous warmer winter (2006/2007). The data sets consist of snow depth, snow weight (water equivalent of snow cover), air temperature, and solar radiation. Each station of SW-Net is paired with a nearby flatland station to compare both meteorological conditions. In this study, we discuss the recent fluctuations of meteorological and snow cover conditions in mountainous areas and compare the results with the measurements obtained at flatland areas.

Comparison results between data in mountainous area and flatland areas show that the fluctuations of winter mean temperature and winter precipitation are almost similar at both areas, while the fluctuations of maximum snow depth sometime show different trend between both areas. Values for the degree-day factor, which indicates the relationship between melt rate and daily mean air temperature, were different from site to site, but their interannual fluctuations were small. The distributions of precipitation with air temperature during each precipitation event in winter show that the peak in each year moves with mean winter air temperature fluctuation, but its pattern shows a similar form.

Data from the last decade are not enough to discuss the influence of global warming on meteorological and snow condition in the Japanese mountainous areas, thus, we should continue to observe meteorological condition in mountainous areas.