Spatial and temporal variability of the frost‐free season in Central Europe and its circulation background

Abstract

The aim of the study was to investigate the temporal and spatial variability of last spring and first autumn frost events as well as the length of the frost‐free season (FFS) in Central Europe in relation to atmospheric circulation. Studies were conducted for the period 1951–2010 using gridded, daily minimum air temperature data obtained from the E‐OBS dataset at 0.25° spatial resolution. To assess the possible impact of air temperature variability on plants, late spring frost events and severe frost events were also examined with respect to the beginning of the thermal growing season. The role of atmospheric circulation was described using Grosswetterlagen circulation types and NAO index, and finally estimated using empirical orthogonal function analysis (EOF). The results confirm a significant increase in the length of the FFS, up to 10 days per decade in the western parts of Europe. This is mostly a result of earlier occurrence of last spring frost in the west up to 5 days. The occurrence of first autumn frost shows no significant trend in most of the studied regions. The obtained spatial pattern of the trends reflects oceanic (west) and continental (east) climatic conditions of the study area. Detailed analysis of circulation types favouring the occurrence of frost in Central Europe indicates that anti‐cyclonic situations are mainly responsible. EOF analyses for the springtime confirm that the first mode, which accounts for 56% of total variance, is related to an extensive high pressure system over eastern Ukraine and Belarus, which brings an inflow of cold, continental air masses to Central Europe. The results provide a broaden information on the region climatologically important due to its transitional location, which may be relevant for investigating past and future trends in spring freeze risk for perennial crops, as changes in the frequency of these airflow patterns will result in changes in the risk of frost damage.

Temporal Variability of Summer Temperature Extremes in Poland

“…Summer maximum temperature is mostly influenced by the thermal conditions of July and August. In June, because of the transitional location of the country, Poland can still be afflicted by late freezes, especially the NE region [44]. Daily maximum air temperatures in June do not exceed 22 °C in general, except for extreme years, as in 2000 when absolute maximum temperatures , reaching 30 °C, were recorded at most stations [45].…”

Atmospheric Moisture Content over Europe and the Northern Atlantic

“…In many areas, it is actually a marginal force, where other weather forces play a major role and this includes local circulation conditions [53]. This explains why the evaluation of the relationship between moisture content and atmospheric circulation was performed herein based on the correlation between TCWV and selected SLP EOF modes.…”

A reappraisal of the thermal growing season length across Europe

“…Several previous studies have related the GSL, and the related frost‐free period or spring onset, to atmospheric circulation at both the hemispheric and regional scales (Jones et al ., ; Qian et al ., ; Strong and McCabe, ; Wypych et al ., ). Such studies are particularly important as any attempt to forecast the GSL is dependent on understanding the linkages with large‐scale, low‐frequency, atmosphere–ocean forcing mechanisms.…”

“…Numerous definitions of the GSL exist, and these often necessarily vary depending on the region under consideration (Linderholm, 2006). A common way of defining the GSL is to calculate the length of time between the first and last frost of the year, where frost is determined from daily minimum air temperatures at or below 0 C (e.g., Robeson, 2002;Kunkel et al, 2004;Yu et al, 2014;Strong and McCabe, 2017;Wypych et al, 2017). Although the frost-free period has relevance for certain regions and for many types of vegetation, a more broadly applicable definition-particularly for midto high-latitude areas (Walther and Linderholm, 2006)-is used by the Expert Team on Climate Change Detection and Indices (ETCCDI).…”