Spatial variability of snow water equivalent in a mountainous area of the Japanese Central Alps

The temporal and spatial variability of the snow water equivalent (SWE) content of the snowpack on an east-west ridge in the vicinity of the timberline altitude in the Japanese Central Alps was examined using snow weights obtained from snow surveys, as well as the chemical stratigraphy in the snow layers, from 22 February 2006 until 18 April 2006. Snow erosion was observed at elevations above 2700 m on the west ridge and at elevations above 2650 m on the east ridge. The SWE below 2600 m on the east ridge was significantly greater than that on the west ridge for the same period and elevation. Further, on the east ridge, 49-55% of the SWE at the 2500-m site and 30-52% of the SWE at the 2200-m site could be explained by snow transport from the alpine area. The SWE at the 2500 and 2200-m sites on the east ridge experienced variations that were 1.7-1.9 times and 1.2-1.3 times those at the 2500 and 2200-m sites on the west ridge, respectively. We infer that the ratio of the SWE on the east ridge to that on the west ridge varies within a constant range throughout a single snow season. The SWE on the west ridge below 2680 m exhibited a good correlation with elevation. Altitudinal distribution of the SWE increased markedly at the upper part of the west ridge (below the timberline) within a time series set of data. The major reason for this fact is a change in the source of the precipitation from the Asian winter monsoon to low pressure passing along the southern coast of Japan. The main wind direction, the existence of the forest area, and the difference in the pressure patterns strongly influence the formation of SWE in the mountainous areas in the vicinity of timberline.