Snow Cover Change

Abstract

The chapter analyses snow cover data for 60 weather stations in Poland: 52 series for the period 1950/51–2017/18 (68 winter seasons) and eight longer series of 80 to 104 winter seasons. Two basic characteristics of snow cover were examined: snow cover duration and seasonal maximum depth of snow cover. The coefficient of variability and absolute and relative trends per 10 years were investigated. The most important results of the study are as follows: (1) year-to-year variability of snow cover duration and its seasonal maximum depth is the largest in regions of poorest snow cover; (2) the number of days with snow cover during the 68 winter seasons has a negative time trend throughout Poland (with a minimum of −4 to −5 days for 10 years in north-eastern Poland); this tendency is statistically significant in most area of Poland except for the highlands and some parts of the mountainous areas; (3) the relative changes in the number of days with snow cover are the most significant in regions with a short duration of snow cover (western Poland; −8 to −10% per 10 years); (4) the maximum depth of snow cover throughout the considered period revealed a negative trend in most area of Poland, statistically significant in the highlands and mountainous areas (−2 to −6%/10y); only in north-eastern Poland is the trend positive, statistically insignificant, (5) in longer periods (80–104 winter seasons), the snow cover duration and maximum snow cover depth are characterised by a slight negative or near zero time trend at most weather stations; (6) in the winter seasons 1969/70 and 1995/96 the longest snow cover duration in most areas of Poland was recorded, while in the 1939/40 and 1962/63 seasons, the maximum depth of the snow cover was the highest. The trend values of snow cover duration in Poland are comparable to similar values averaged over the Northern Hemisphere, where the duration of the snow season has declined by 5 days per 10 years since the winter of 1972/1973. On the other hand, the negative trend of maximum snow cover depth is not as significant in Poland as the European average, which is −11.4% per decade.