Abstract
Snow accumulation in the mountainous area of the Jyoetsu border (between Gunma and Niigata Prefectures) has been decreasing recently. A vegetation change was also pointed out on Mt. Hiragatake near the center of this region. This vegetation change might have been caused by the decreased snow accumulation. However, because there have been few weather observations in this area, the continual change in snow accumulation has not been clarified. To determine the changes in snow depth on Mt. Hiragatake from the past to the present, the depth in the past was estimated from the record at lower elevations. It was found that snow depths on Mt. Hiragatake have been decreasing over the long term. Weather factors related to snowfall were also examined. Generally, the total snowfall during each winter depends on the frequency of the winter-type atmospheric pressure pattern over Japan. The frequency has been increasing over the long term, although snow accumulation has been decreasing. The reason for this discrepancy is the rise in air temperature in winter. It should be noted that only the surface air temperature but also the upper air temperature is rising. It is concluded that the rising temperature of the surface and upper air in winter causes the reduced snow accumulation.
