[M-IS12] Mountain Science

[MIS12-P12] The distribution of snowfall amount and snow depth in Kamikochi, the Northern Japan Alps

*Hikaru Kondo¹, Motoshi Nishimura¹, Akihiko SASAKI², Keisuke Suzuki¹ (1.Shinshu University, 2.Kokushikan University)

Keywords:seasonal snow cover, snowfall, alpine region, in-situ observation, Japanese Alps

Snow covering mountainous areas plays an important role as a water resource. Snowfall is expected to increase in the future due to global warming, and its distribution and fluctuation are affected by the complex topography of the mountains and the atmospheric pressure pattern. In this study, we analyzed meteorological observation data on climatic conditions in and around Kamikochi from winter 2014 to winter 2024 to clarify the fluctuation in the spatial distribution of snowfall amount in Kamikochi, a basin-like terrain in the mountainous area, as affected by the pressure pattern and surrounding terrain. As a result, no trend of increase or decrease over time in snowfall and snow depth was observed during the analyzed period. The snow depth was not simply fluctuating depending on elevation or year, and the variation of the snow depth between observations sites varied from one snowfall event to another. Furthermore, even though the snow depth observation sites were located within a local space of approximately 10 km square, there were days when there was no snowfall at a certain site and snowfall at other sites. These results suggest that the spatial snowfall depth may vary from one snowfall event to another. In addition, the number of annual occurrences of pressure patterns that cause snowfall events was not uniform during the analysis period, and there was no trend of increase or decrease over time. The frequency of snowfall depth ratio for each pressure pattern was calculated, and it was found that the pressure patterns showing a tendency toward heavy or light snowfall differed from one location to another. Furthermore, wind direction frequency analysis was conducted for the pressure patterns that showed a tendency toward snowfall, suggesting that the surrounding terrain may influence the spatial distribution of snowfall depth. Therefore, we examined the effect of terrain on the advected air masses. The results suggested that the points where heavy snowfall occurs in mountainous areas has a relatively higher elevation mountain on the leeward side of the point than on the upwind side and (a) If the wind is blowing over the downwind side of the mountain, the point just below the slope, (b) If the wind does not cross the mountains on the downwind side, a relatively large area on the upwind side of the slope, not only just below the slope. In addition, the comparison between the winter type and south coast pressure suggests that there is a tendency toward heavy snowfall in the delay just below the west-northwest slope of the mountains during winter type, over a relatively wide area on the upwind side of the mountain slope during south coast pressure. These results indicate that the spatial distribution of snowfall in mountain basins and valleys is affected by the pressure pattern. In addition, the spatial distribution of snowfall in mountain basins and valleys may be affected by terrain effects on air masses, which are estimated from the difference in elevation between the downwind and upwind sides of basins and valleys, in addition to wind direction and speed that vary with each pressure pattern.