Abstract
From February 8 to 9 and 14 to 15 in 2014, Tokyo was covered with 27-cm-deep snow (Tokyo Meteorological Agency). Owing to heavy snow load, many buildings were damaged on February 15. During the two periods of snowfall, we measured the snow density in central Tokyo and obtained values of 122 and 130 kg m−3 on February 8 and 258 and 270 kg m−3 on February 14. The damage that occurred on February 15 was explained by a two-fold difference in snow density between the two periods, which was caused by the fact that the snowfall changed to the rainfall through the sleet-fall. From February 14 to 15, rain water remained within the snow cover, whereas from February 8 to 9, there was no rain water. On February 14, we measured the snow density on both the ground and the roof of a 170-m-tall high-rise building in Otemachi. We observed a snow density of 270 kg m-3 on the ground at positive temperature in the Celsius scale and a snow density of 144 kg m−3 on the rooftop at a negative temperature in the Celsius scale, which constitutes a large difference in density. In a region with snowfall as less frequent as in Tokyo, it was clarified that the amount of snow-load is best approximated by the cumulative precipitation because snow cover occurs. This approximation method was applied for Tokyo, Kumagaya, and Kofu, where the snow-load was calculated using time-series hourly data of snow depth and precipitation for the past 24 winters. The return periods of snow-load were then obtained for the three cities. In conclusion, the peak snow-load of 941Nm−2 （=96mm）on February 15 in Tokyo was estimated to occur once in 240 years.
