Changes in extreme nival conditions in Poland during the second half of the 20th century

Abstract

The two main objectives of this study are: 1. to assess the scale of extreme nival conditions in Poland; 2. to provide a fragmentary, regional verification of the IPCC thesis of the increasing frequency of extreme atmospheric phenomena during recent decades, by the estimation of extreme nival conditions tendencies in the second half of the 20 th century. The daily data of snow cover depth in 12 meteorological stations in Poland, for the period 1954-2001, were analysed. A winter season with extreme nival conditions is the season, when the snow cover duration value and/or the maximum seasonal snow cover depth value, was of the empirical probability of 90 % (a season of extremely long duration and/or thick snow cover). A slight negative, usually statistically insignificant, trend was found for characteristics concerning extremely abundant snow cover, i.e.: the seasonal number of days with snow cover of a considerable depth; the 90th percentile value of the daily snow cover depth for the period from December 1 to February 28; the seasonal maximum of a 24-hour increase in the snow cover depth (except for northern Poland); the seasonal number of days with a 24-hour increase in the snow cover depth of > 10 cm. At the same time, since the 1970's the scarce snow cover (i.e. of the empirical probability < 10 %) has been observed much more frequently than before. The above mentioned IPCC thesis has been confirmed towards the extremely low snow cover values in Poland.