Effects of Global Warming on Climate Conditions in the Japanese Alps Region

Abstract

The region of Japan that lies along the Sea of Japan is known to experience some of the heaviest snowfall in the world. In this region, precipitation brought by snowfall is more important as a water resource than rainfall. During winter, a thermal anticyclone is formed over the Siberian continent by strong radiative cooling. The Tibetan Himalayas towering to the south block the anticyclone southward advance, the advance is enhanced during the winter at low solar elevation angle. When the warm Tsushima Current pours into the Sea of Japan heading north, the cold, dry air mass blowing out of the Siberian anticyclone toward the east becomes unstable, absorbing heat and moisture vapour from the lower layer. This produces cumulus convections in sequence, which land on the northwest coast of the Japanese islands. In cumulus clouds, high moisture rates and cold temperature accelerate the formation of snow particles. In addition, these clouds hit the high mountains that run along the center of the Japanese Archipelago and are forced to climb upward, bringing a much larger amount of snowfall. Therefore, the mountain range experiences exceptionally heavy snowfall that is extreme even by world standard, and in spring, the melting snow becomes a valuable water resource for the region. Snow plays the role of a natural white dam by accumulating in watersheds during winter. Recent studies have reported that the amount of snowfall in Japan will decrease as a result of global warming (Inoue and Yokoyama, 2003). However, these studies used data observed at low altitudes. The question arises whether the same theory can be applied to high-altitude mountain areas. In a temperate snow-covered area where rainfall is observed in winter or where the temperature is above 0 °C and the snow melts, the temperature often reaches the threshold point, which is the boundary line between snow and rain. At this point, a slight temperature increase or decrease can change snow into rain or, conversely, increase the snow. This means that global warming seems to cause a decrease in snowfall even if the amount of precipitation stays the same, because the snowfall particles melt, transforming into rainfall during precipitation. However, it is possible that even with a temperature rise of several degrees 100 years from now, the amount of snowfall could increase in mountain areas at high altitude where we predict that the temperature will not increase up to the threshold temperature between snow and rain. Inoue and Yokoyama (2003) stated that the amount of snowfall in Hokkaido, at the northern latitude of 41.5o or above, will not change much even after 100 years of global warming. However, in a chart presented in their report,