| Summary: | The present study investigates the regional features of a highly recurrent winter meteorological phenomenon, with costly and adverse effects on the croplands of the Romanian Plain, one of the most important agricultural regions of Romania. The analyses are focused on the characteristics of air and ground frost, but also on their joint action, for understanding the exposure to cold stress of croplands in a changing climate. The study uses the daily minimum air temperature and mean daily surface soil mean temperature of the gridded ROCADA dataset (1961-2013), extracted for 10 representative weather station locations from the corresponding grid cells, to compute five relevant parameters of air and ground frost and to analyse subsequent trends in their variability across the region. A Mann-Kendall trend analysis (MK) was also performed for each air and ground frost-related parameters to study the changes in cold (freezing) stress at regional scale. The study presents the climatological traits of air and ground frost across the region, typically affecting it from mid-to-late autumn until early-to-mid spring. Air frost season is generally longer than the ground frost season, in relation to its earlier autumn onset and later spring offset dates. The region has a moderate exposure to frost damage risk of crops when considering the seasonal frequency of joint air and ground frost action days. MK analysis for the selected air and ground frost parameters revealed mixed trends, mostly with no statistically significance and some of them disconnected from the ongoing climate warming which affects the region. The changes frost parameters, mainly in those related to ground frost, could partially explain the expansion trend of the agricultural growing season, as well as some changes in crop development stages, especially of cereal crops.
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