VARIABILITY OF FREQUENCY OF STORMS AND HAILSTORMS IN THE PERIOD 1961-2004

Abstract

Severe storms with hail can cause major damage to a crop, especially in the vegetational period, when the kinetic energy of hail particles is the largest. A spatial and temporal analysis of storm and hail frequency in the vegetational period was performed to find the temporal variability and trends in the observational period 1961-2004. The time series of 44 years was long enough to detect significant changes in storm and hail occurrence all over Slovenia. Temporal trends were calculated at observation points. Additionally, the long-term spatial distribution of hail frequency in the last 14 years was compared to that of the reference period 1961-1990 (Figure 2). A spatially homogeneous decrease of storm frequency was detected in Primorska, Dolenjska and Bela krajina (Figure 2). On the other hand, storm frequency had increased in Prekmurje and Goričko. In other parts of the country, there is no uniform trend in storm frequency for larger areas. In parallel with a storm decrease, the frequency of hail had decreased in the costal region and in Bela krajina (Figure 7). In the last 14 years less hail was also observed in parts of Štajerska and at the southern edge of the Julian Alps. A positive trend in hail frequency was observed in Goriška brda, in the central part of Slovenia with Bloška planota, in a small part of the Karavanke and in some parts of Štajerska.