Forest Influence on Snow Accumulation at Strong Wind Location (II) - Snow Accumulation in Few Snow Movement Season -

1990

S. 145-175

16 Abb., 10 Tab., 18 Lit. Ang.

Unselbständiges Werk

200037156

The distribution of snowcover in the mountain areas of the northernmost part of Hokkaido was investigated to clarify the influence of forests on snowcover and the movement of meltwater in the thawing period. The areas in question are characterized by strong westerlies and cold temperatures in the winter season (e.g. the maximum wind velocity and the minimum temperature in the winter of 1985 in the Souya hills were 32.0 m/sec and -20C, respectively) . In the winter of 1988 (from October in 1988 to April in 1989), however, the temperature of this region was high compared to average winter temperatures and the degree of snow movement by wind was small. The purpose of this study is to examine the influence of forests on the accumulation of snow, the ground's freezing and the melting of the bottom layer of the snowcover during this mild winter. Two study areas were selected for the investigation of windy sites. One is the Sannaigawa basin in the Souya Hills and the other is the upstream of the Doran-gawa basin in Nakagawa Town. The same investigation was also carried out in the forests near Toikanbetu town where the influence of wind on the accumulation of snow was weak. The weather in northern Hokkaido during the period of observation was different from average winter in the following ways: 1) Monthly mean temperatres were 4-5C higher; 2) The snowcover of this region (130-160cm deep in usual winters) was 50-60cm less; 3) The period of continuous snowcover was 15-45 days shorter; 4) The days on which strong winds blew were few. At the Souya hills, for example, the number of days whose mean wind velocity exceeded 10m/sec decreased from 48.2 (an average winter) to 22 (the winter examined). Because of these weather conditions, there was little snow movement and drifting in the winter examined. The results of the investigation are summarized below. Just as in an average winter, the accumulation of snow in this mild winter was also influenced by the topographic features of the study area. There was only a very small quantity of snow on the hilltops, but the amount of snowcover increased on lower hillside slopes and at the bottoms of valleys. On the grassland area of hilltops subject to strong winds, the amount of snow cover was close to 0cm. On the other hand, there was much snowcover in the forested part of hilltops adjacent to the grassland areas. This finding indicates that forests have the effect of allowing the accumulation of snow even in winters in which there is little snow movement and drifting. In evergreen coniferous forests at windy sites, although a large amount of snow is present in ordinary winters, there was only a small amount of snow in the winter examined, this amount being about half of that in deciduous forests. As for the coniferous forests not affected by strong winds, the amount of snow was not only less than that in ...........