Forest Influence on Snow Accumulation at Strong Wind Location

1989

S. 801-828

14 Abb., 11 Tab., 36 Lit. Ang.

Unselbständiges Werk

200037124

Snowcover in mountainous areas and the influence of forests on snowcover in windy and cold districts such as northernmost Hokkaido have not been sufficiently investigated. The purpose of the present investigation is to clarify the processes of the accumulation of snow, freezing of the ground's surface and movement of water during thawing periods in windy and cold districts. Two main investigative areas were utilized for the research. One is the Sannai-gawa Basin in the Soya Hills, in northernmost Japan, where the strong winds blow through gentle hills. The other is the upstream area of the Doran-gawa Basin in Nakagawa Town, which is inland of the northernmost part of Hokkaido, where strong winds from the Teshio River hit the land directly. Snow observations were carried out in these area during two winters, 1986-1987 and 1987-1988. Snow sampling was mainly carried out between the end of February and beginning of March when the snow cover reached it's maximum level. However, especially in the Doran-gawa Basin, snow sampling was carried out throughout the winter season. The result of the investigation is summarized below. In the windy and cold districts, the snowcover in mountainous areas is subjected to large fluctuations. The topographic features present are a major factor affecting snowcover distribution. Ridge areas have a very small quantity of snow, and the amount of snowcover increases on lower hillside slopes and at the bottoms of valley. In addition to these facts, forests were found to function effectively as areas of snow accumulation. This function was particularly evident on ridge areas where strong winds transport loose snow. If the snowcover is at more than a certain depth, such as in forests, it shuts out the cold open air and keeps the ground's surface from freezing (at a freezing index of 700, 1,000C.day). Although generalizations are difficult because this investigation was conducted in districts where there was much snow movement, drifting and so on, 50cm of snowcover seems sufficient to keep the ground's surface from freezing. On grasslands on which snow movement occurs with frequency, the freezing of the ground's surface was shown to happen even under snowcovers of more than 80cm. But the freezing of the ground's surface did not occur even under snowcovers of 50cm forests which had little snow movement. At the places where the ground's surface did not freeze, the melting of the bottomlayer of the snowcover was observed. At such points, much seeping water was supplied to the soil layer ever during the coldest weather. Water seepage kept the soil in the forests from drying up all through the winter season. The damp soil layer allows for sufficient conditions of permeation during the thawing period in the early spring. At places where the ground has been frozen, most of the water produced from thawings runs off of the ..... ISSN 0367-6129