Frost depth in Japan during the winter season from 2011 to 2020

Since 2011 winter season, frost depths have been measured in Hokkaido, northern part of Japan, where the seasonal ground freezing occurs. Frost depths were measured in schools as the outreach program. At schools, measurements of frost depth were made once a week using frost tube by students or teachers under no snow-removal (with snow) condition.

In 2011 winter, we started measurements at three schools, and the number of schools extended to 36 in 2019-2020 winter season. The measured frost depths ranged widely, from only a few centimeters to more than 60 cm. However, some schools had no frost depth due to heavy snow. We confirmed that the frost depth strongly depends on weather condition, especially snow depth and air temperature.

At one elementary school in Tokachi District, Komaba Elementary School, measurements have been made almost every day for seven seasons, from 2013 -2014 to 2019-2020 winter season. The maximum frost depths ranged from 15 cm to 40 cm, which strongly depended on the snow amount, especially that in December. However, the relationship between the maximum frost depth and air temperature has no significant correction in this school.

In order to validate the effect of snow on frost depths, in addition to normal measurement with snow condition, we tried to measure frost depths under snow-removal (without snow) condition at the same school, Teshikaga Elementary School, in 2018-2019 and 2019-2020 winter seasons. The maximum frost depths were 28.0 cm with snow (maximum snow depth: 33 cm) and 54.5 cm without snow in 2018-2019, and 27 cm with snow (maximum snow depth: 20 cm) and 34 cm without snow in 2019-2020. It was confirmed that snow has a role as insulator and affects the frost depth.