Assessment of the Recent Tendencies of the Winter Precipitations and the Snow Cover in Bulgaria

Snow is an essential meteorological element and also an indicator of the fluctuating climate, resulting from change in the regime of winter precipitation and air temperature. Taking into account the recent tendencies of a warming climate, it is important to quantify these changes and their influence on snow amount and duration, which have significant consequences on several economic and environmental aspects.

Data from 20 stations with altitudes ranging from 50 up to 2925 m a. s. l. for the period 1961-2017 have been used for testing of the following winter characteristics: mean monthly air temperatures, days with snowfalls, days with rains and days with mixed precipitation and the corresponding monthly precipitation amounts. The air temperatures during snowfalls have been also examined. Except for the stations at highest altitudes (above 2000 m) no significant trends in precipitation quantities have been found. Decreasing trends of the days with snowfalls and the opposite for the days with rain and mixed precipitation have been detected. Almost all of stations show also increasing trends of the air temperatures both monthly as well as event based. Most of these trends are significant at 0.05 level. One secondary effect of this temperature rise is the enhancing of the severe wet snow events, which have been considerably intensified recently.

Another 35 stations with long data sets (1930/35 – 2019) have been used to evaluate the following snow characteristics for 3 main climatological reference periods – 1931-60, 1961-90 and 1991-2020: days with snow cover, averaged and maximal snow depth. No significant change for the maxima has been detected but the comparisons of other two variable depict significant differences.

This study has been funded by the National Science Fund in two separated projects under the contract numbers DM14/1 in the program for junior researchers and post-doc and KP-Austria-2 in the bilateral scientific program with Austria.