High-resolution hail monitoring in an alpine fruit-growing region

The hail monitoring network in Trentino has been uninterruptedly run since 1974. It consists of 271 impactometric measurement sites, arranged according to a regular grid having a 2-km side. The survey allows an estimation of the kinetic energy of the hailstorm. A well known correlation exists between the electric activity of thunderstorm cells and the amount of hail fallen during hail-bearing events. In this study two aspects are considered: i) the relationship between ground lightning measures and hail indices; ii) some spatial and altitudinal features of hail climatology. Hail data were annually aggregated (in one season, from May to September). The correlation of hail indices with elevation is clear, yet it cannot explain by itself the inhomogeneous distribution in some areas, where local features significantly affect hail occurrence. Also the statistical link between annual hail values and the total measured number of lightning strokes is good; for some it is highly significant (p<0.01) after the removal of respective time trends. This allows to candidate the use of the number of lightning strokes over a season as a good indicator of hail fallen in the same season.