Revision of climatic division for Japanese snowy areas based on the new climatic data mesh climatic data of Japan and studies on climatic responses of Japanese snowy areas to recent climatic change

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We could complete the climatic division based on their snow-cover characters in mid-winter of all snowy areas over Japan and draw up a new digital cartographic map for the climatic division, using the newly developed mesh climatic data Mesh climatic data of Japan. In this revision we could improve the definition and conditions for depth-hoar region, one of the categories for our climatic division, to clarify the climatic implication more precisely according to observed data. New definition indicates the rates of numbers of winter seasons in which depth hoar developed to significant level that was distinguishable as the depth-hoar region, during climatic period (30 years).We also investigated relationships in monthly climatic values among maximum sow depth, mean air temperature, and precipitation of snowy areas using data set obtained by the official meteorological observation sites. The results reveal that these quantitative relationships closely relate to our climatic division. For example, the upper limit of monthly maximum snow depth found in the climatic data of the sites in wet-snow region could not hold in other colder climate regions.Moreover we could clarify responses of Japanese snowy areas to the recent warmer winters, comparing normals (climatic values) from 1961 to 1990 with that from 1971 to 2000. Drastic changes were found in the maximum snow depth of heavy snowfall areas in the wet-snow region. It shows that such warmer heavy snowfall areas are very sensitive to climatic changes and that climatic responses also relate to the climatic division introduced in this study.