Hail occurrence in Italy: Towards a national database and climatology

Abstract

Although the effects of hailstorms usually interest limited areas, the damages can be severe. These, damages can be potentially reduced by a reliable hailstorm forecast. In Italy, only few regions have a network for monitoring hail events, the coverage of these networks is limited to small areas, and long-term and nationwide time series of hail events are not available, therefore the chances of improving the quality of the hail forecast are severely reduced.The aim of the present study is to collect data and information from different sources on hailstorms in order to evaluate the annual hailstorm frequency in Italy. In order to obtain more complete information about the hail distribution, different datasets have been used: i) daily information about hailstorm occurrence at fixed meteorological stations from the NCDC dataset; ii) events information (date, location, and hailstone size) obtained using hailstorm reports available from different agencies. In this study the hail events are classified according to the hailstone size, then a statistical approach is used in order to evaluate the mean annual frequency of the events at the municipality scale for each hailstone size class. The atmospheric parameters, known as hailstorm precursors, are estimated using the NCEP/NCAR daily reanalysis at 2.5degree horizontal resolution.As a final result, this study presents a step forward towards a climatology of hail frequency in Italy at municipality scale for the period 1971–2009.