Frost risk indicator analysis in Sopron wine region (1961–2016)

Füzi, Tamás and Ladányi, Márta (2020) Frost risk indicator analysis in Sopron wine region (1961–2016). IDŐJÁRÁS / QUARTERLY JOURNAL OF THE HUNGARIAN METEOROLOGICAL SERVICE, 124 (4). pp. 447-462. ISSN 0324-6329

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Abstract

A characteristic symptom of climate change is the modified distribution of frost events that has fundamental effect on agricultural production. To learn these changes in Sopron region, Hungary, we investigated daily minimum and maximum temperature data of the period 1961–2016 provided by the Hungarian Meteorological Service. The time interval 1961–2016 was split into two (1961–1990 and 1991–2016) in order to compare nearly two climate cycles statistically. We analyzed the 56-year trends of the last frosty day of spring and the first frosty day of autumn as well as the length of the longest yearly frost-free period. As for the winter period (October 16 – February 28), the frequencies of four different strengths of frosty days were examined. We analyzed how often an uninterrupted frost-free period (Tmin>0 °C) longer than 12 days developed between two frosty periods in spring and in autumn, exactly when it occurred (Julian day), and how many days it lasted for. Finally, we investigated the trends of the yearly numbers of spring frosty days and their variances. Amongst others, we show that the length of the longest uninterrupted frost-free periods has increased significantly over the past 56 years, with 70% of years in the recent climate cycle (1991–2016) having frost-free periods of more than 200 days. As an average change per 10 years, the last spring frost period ended four days earlier, while the onset of autumn frost shifted 2 days towards the end of the year. The number of days with minimum temperatures below -15 °C, -10 °C, -5 °C, and below 0 °C decreased significantly during the dormant period. These changes mean a prolongation of the growing season, partly a reduction of the winter regeneration period, and the potential higher overwintering success of the pests. The number of spring frost days also decreased significantly, while their variability has grown markedly.

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