Abstract
Long-term variations and trends in the annual maximum snow depth and snow cover duration were analyzed for Niigata Prefecture between the winters of 1941/42 and 2012/13. Analysis was conducted on daily snow depth data from 17 snow observation sites, ranging in altitude from 4m to 507 m, and both the simple linear regression analysis and the Mann-Kendall test were utilized as means to detect trends. Statistical significance of the trend in this study was evaluated at a level of significance of 5%. The results showed that the annual maximum snow depth is on a decreasing trend in the plain area, which has an altitude of 30m or less, while no significant trend is seen in the mountainous area. The rates of decrease range from 2.3 to 12.8cm every 10 years. It is considered that decreases in winter precipitation and rises in winter temperature are likely to be related to the decreasing trend in the annual maximum snow depth. In addition, a decreasing trend in the snow cover duration was observed at the stations analyzed in this study, which have an altitude of 350m or less; rates of decrease range from 1.7 to 7.5 days every 10 years. In the plain area at an altitude of 30m or less, this decreasing trend is believed to be primarily due to the significant increase in air temperature in February and March.
