In recent years, the number of days with hail damage occurrence determined by the number of settled claims of the SparkassenVersicherung AG insurance company has significantly increased. This poses problems especially to insurance companies, the construction industry and agriculture.
According to the fourth assessment report conducted by the Intergovernmental Panel on Climate Change (IPCC; IPCC, 2007), the global mean temperature increased in the last century (1906-2005) by about 0.74°C (±0.18◦C). This raises the question whether there is a link between temperature and changes in the hail frequency, as well as what can expected for the future. However, estimating the hazard associated with hailstorms is very difficult. As thunderstorms and related hail streaks are often limited to a typical horizontal extent of only a few kilometers, they are regularly not captured by current surface observations systems. Additionally, remote sensing instruments, such as radars, are not yet able to detect hail, as no unique relationship between radar reflectivity and hail is established (Sauvageot, 1992; Kunz and Puskeiler, 2010). Furthermore, thunderstorms are mainly not captured in climate models because their horizontal extent is less
than the spatial resolution of the model data. Hence, single- or multi-cells cannot be resolved by most models at all. Thus, there are basically no available time series of thunderstorm and hail observations that would allow to analyze their changes over an adequately long time period. To overcome this problem, the parameters that are important for convective initiation, which are better understood and better measurable, can be used to determine the potential of thunderstorm development. These parameters describe thermal stratification of the atmosphere, moisture content and meso-scale uplift. Changes in these parameters are assumed to impact the probability of thunderstorm occurrence. Furthermore, these parameters can be linked to different large-scale weather patterns, which then favor to a certain extent the development of hailstorms. The overall goal is to examine to what extent specific weather patterns can be related to damage-causing hailstorms as well as to study the natural long-term variability and periodicity of these specific patterns in the past and in future decades.