CHARACTERISTICS OF FIRST AND LAST FROST OCCURRENCES AND THE LENGTH OF FROST-FREE SEASON IN BULGARIA

Due to recent climate change the interest to the investigation of extreme weather and climate events has been increased during the last decades. The time of the occurrence of the last spring frost (LSF) and the first fall frost (FFF) determine the length of frost-free season (LFFS) which affects significantly various aspects of human activity and in particular the agriculture. The objective of this study is to analyse the spatio-temporal variability of the occurrence of LSF and FFF and to identify the changes in the LFFS. The study is based on the minimum daily air temperature data from eight meteorological stations in Bulgaria for the period 1989-2018. In order to examine the changes in LFFS the linear trend has been calculated for each station and for regional (Northern Bulgaria and Southern Bulgaria) time-series. The synoptic situation for the days with LSF and FFF are analysed. The results form study show general tendency to the increasing of the LFFS which is related mainly to earlier occurrence of LSF. Despite of general positive tendency of the LFFS at regional scale due to the local physical-geographical features for some stations the trend of LFFS is negative. The results from the investigation could be used for reduction of frost disaster and for the formulation of policies and measures for adaptation of agriculture to climate change.