Frost Probability Data for Agricultural Planning in the Elbe River Lowland

This section discusses probability data related to frost temperature occurrences for 116 grid points with a horizontal resolution of 10 9 10 km. The aim here is to summarise the probability for all grid points of the three classes of frost severity at a later date in the spring and earlier date in the fall and the probable length of the FFP. The dates of the last spring frost and the first fall frost, for several probabilities and for the three classes of frost severity as derived using the Pearson type III distribution, are presented in Table 5. As indicated in Table 5, the probability of the occurrence of the LSF decreases with increases in intensity. At a 50% probability level, the ending of mild, moderate and severe frosts in spring will be on or earlier than day 112 (22 April), day 103 (13 April) and day 98 (8 April), respectively (Fig. 7a–c). The occurrence of frosts in May is very dangerous from the perspective of agricultural production. At the 96% probability level, the last mild spring frost occurs in the Elbe River lowland on 20 May and earlier; moderate frosts occur on 13 May and earlier; and severe frosts occur on 6 May and earlier. At the 90% probability level, the LSF ends by mid-May. There is a 10% chance of a late mild spring frost after 12 May, but a 90% chance that a frost is expected to occur on or earlier than 12 May during the spring season. The last mild frosts may occur on average, with 80% probability, on 5 May, and the last moderate frosts may occur on 27 April and severe frost on 21 April and earlier (Table 5). Consequently, there is a 20% chance of the occurrence of dangerous spring frosts during the planting of field vegetables after 5 May. In addition, most vegetables grown in the warmest areas fall within the low-risk category for severe spring frosts. Conversely, Table 5 also shows a very low probability for the occurrence of the FFF in September. The first mild fall frosts occur with 96% probability on 22 September and later; moderate frosts occur on 29 September and later; and severe frosts occur on 4 October and later. Thus, there is only a 4% chance that the first frost in the fall will occur before 22 September (mild), 29 September (moderate) and 4 October (severe). There is a 90% chance that the first mild frost occurs on or after 30 September. Mild fall frosts in September appear only sporadically, but severe fall frosts in September did not occur, except for two cases (24 September 1964 and 29 September 1970). A significantly higher frequency of mild first fall frosts occurs in the second half of October. There is a 67% probability of mild fall frosts beginning on or later than 13 October, moderate fall frosts on or later than 21 October and severe fall frosts on or later than 25 October. At the 50% probability level, the beginnings of mild, moderate and severe fall frosts will be on or after day 293 (20 October), day 302 (29 October) and day 305 (1 November), respectively.