Climatic response of snow depth to recent warmer winter seasons in heavy-snowfall areas in Japan

In heavy-snowfall areas facing the Sea of Japan, winter seasons with lower volumes of snow occurred from 1986/87 to 1999/2000. In this paper, the changes induced by these warmer winters in snowy areas in Japan are investigated using two datasets. One set was normalized for the period 1971-2000 from manned surface meteorological observations by the Japan Meteorological Agency, and the other set was for 1961-90. Winter climatic monthly values for the first dataset were thought to be affected by the warmer winter seasons since almost half the relevant period coincides with them. By comparing each monthly climatic value in both datasets, the following results were obtained: (1) At each meteorological observation site the bimonthly average temperature from January to February increased and the amounts of increase were about 0.4 degrees C on average. (2) The bimonthly maximum snow depth for the same period increased at a number of sites, but usually by only a few centimeters, the maximum increase being 0.05 m. (3) In contrast, the decreases in snow depth in heavy-snowfall areas facing the Japan Sea, which belong to a temperate climate zone, were large, ranging from about 0.05 to 0.22 m in climatic bimonthly maximum snow depth during January and February. The last result shows that snow covers in such warm snowy areas are very sensitive to climatic changes. An attempt is also made in this paper to estimate the amounts of decrease in snow depth from the increases in air temperature and the decreases in precipitation amounts.