The probability of winter and spring frost damages experienced in peach and apricot plantations has been assessed in 5 growing regions of Hungary (Szeged-Szatymaz, around the lake Balaton, Mecsekalja, hills of Buda, Mátraalja) and (Mecsekalja, hills of Buda, PestGodo116, Duna-Tisza Mize, Matra-Bükkalja) during the period between 1951 and 20...00.
Frost tolerance of flower buds on a given shoot sample is expressed by the mean value assessed after frost damage (LT50), and the meteorological records of the growing sites raised between 1951 and 2000 are used to calculate the probability of frost damage. In peach, the difference between growing sites and between varieties may become two fold as for the chance of repeated frost damage at a probability of 50 %. In apricot, the probability of frost damage may exhibit differences between growing sites up to 20 % as for susceptible varieties, and 16 % for frost tolerant varieties. Frost damage may vary between 4 and 18 % depending on the genuine frost tolerance of the varieties. Peach is afflicted by low temperature causing substantial losses of yield at the highest probability in the region Szeged-Szatymaz and at the lowest in Mátraalja. Apricot is, on the other hand, most endangered in the Duna-Tisza Mize region, while the lowest probability of frost damage is expected around Mecsek and Buda.
The critical period of frost damage in the mid of January in Szeged-Szatymaz region, in Mecsekalja the mid of February showed the highest probability of frost damage. All growing sites are frequented at high chances by frost damages occurring during and closely after the blooming period. Duna-Tisza köze is mainly afflicted in early March, whereas Mátra-Bükkalja in mid of January and each March.
The probability of temperatures below zero degree has been assessed in all the 5 regions observed. Around April 5-8 the probability of freezing temperatures diminishes steeply at all sites, whereas the risk of frost increases again around April 9— 11. That climatic peculiarity of should be taken into consideration in choosing growing sites or varieties.
Postulating the effects of a global warming up of the climate, the chances of avoiding frost damages at different growing sites by delaying the blooming dates are considered. According to our calculations, the delay of blooming by 5 days may diminish the risk of frost damage by 4-20 % at the growing sites examined, whereas a delay of 10 days reduces the risk by 37-85 % in both fruit species.
Calculations offered an answer on the question of climatic changes, whether the probability of winter and spring frosts damage changed during the 50 years. The long list of data shows the diminishing chances of winter frosts, while the probability of temperatures risking spring frost damages increased after the early 1970-es up to now.